Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/iwem52897.2022.9993495

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DOI： 10.1109/iwem52897.2022.9993610

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Authorship：Corresponding author   Language：Venda   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

<p>In Japan, the number of water accidents is approximately 1,300 per year, which is almost constant in recent years. Although divers rescue people in the case of water accidents, there are various obstacles in the sea. Then, divers are always surrounded by a lot of dangers in the rescue activities. Therefore, assuming that identifying the locations of divers supports their rescue operations, we investigate an undersea positioning system using radio waves in the VLF band (10-kHz). According to previous research, radio waves of 10-kHz are theoretically attenuated at 3.5 dB/m, and can be transmitted in the distance of 30 m and more. In addition, a numerical simulation of a three-dimensional undersea position-estimation system has already been reported. In this study, we measured received signals at the real sea and showed the position-estimation results employing the algorithm for an undersea position estimation.</p>

DOI： 10.1587/comex.2021xbl0092

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Under-the-ice survey with underwater robots in Arctic is important to understand the global warming mechanism. We are currently studying localization method under-the-ice because acoustical positioning system does not use there. In this report, a new method of under-the-ice localization is proposed.</p>

DOI： 10.1299/jsmermd.2020.2P2-I05

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© 2019 Antenna Branch of Chinese Institute of Electronics. A wireless power transfer (WPT) technology is expected to be applied to powering electric vehicles in the kHz band. The specific absorption rate or SAR may be used as a metric to ensure the safety of WPT devices. In order to measure the specific absorption rate, it is necessary to calibrate the electric field probe, that is, to relate the received electric field intensity with the output voltage of the probe. In this paper, we theoretically and experimentally verify that the electric-field probe calibration method we developed in the MHz band can be applied to the kHz band as well.

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In order to evaluate the specific absorption rate for wireless devices in the MHz band, we propose a method to estimate the electric field intensity generated by small dipole antenna in saline solution using the transmit antenna factor based on the power transfer formula and two antenna method. By introducing the average electric field intensity, we solve some problems caused by inappropriate approximation in our formulation. By comparing the results of numerical simulation and measurement, the validity of the distance property of the transmit antenna factor of the small dipole antenna in the solution is comfirmed. In addition, an example of probe calibration using the small dipole antenna based on our proposal is presented.

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A serious problem in evaluating the radiation efficiency of antennas based on Wheeler cap method is to emerge some dips in the efficiency at the cavity resonance, because a shielding cap can be considered as a cavity. To eliminate the dips, it is shown to be effective that a rational function is fitted to measured reflection coefficient and common polynomial factors which depend on the cavity resonance are canceled. In this paper, we describe the cancelling condition in detail by using equivalent lumped circuits for the cavity. And, the effect of the fluctuation of measured reflection coefficient inside the cavity can be reduced by using hamming window in the process of curve fitting. Our modification is affirmed by estimating Wheeler efficiency of simple antennas.

DOI： 10.1109/CAMA.2017.8273466

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In 1998, JAMSTEC started the development project of the first prototype of a long-range cruising AUV (LCAUV) to evaluate fundamental technologies needed to travel through under the ice covered area of the Arctic. In 2005, The LCAUV, Urashima, achieved 317 km continuous cruising powered by a deep sea fuel cell developed in JAMSTEC [1]. We then moved to next stage and have conducted to design the second prototype LCAUV with target range of over 3,000 km. It included improvement of power source, communication system, and positioning system. In 2010 a small high efficiency multi-less (HEML) fuel cell was completed [2] and a long range acoustic communication system achieved 1,000 km communication using time-reversal waves. But we had not developed practical positioning system for under the ice by 2010. In past years the dramatic melting of Arctic ice would be driving extreme weather. This is very serious problem, but it is still poorly understood. Scientists need more research to understand it. We have thus a plan to develop an Arctic research platform that especially performs observations under the ice. Now we are conducting a research of a new positioning method with communication availability before developing the platform or an AUV. The proposed method is based on low frequency electromagnetic waves which can propagate inside of ice and sea water. A prototype to evaluate the method is like GPS repeater. The repeater to be set on the ice receives GPS signal, transmitting radio waves into the sea water via the ice up to several tens meters deep. To realize the system feasibility we started developing underwater antennas and measuring wave propagation in the sea ice and the sea water in 2016.

DOI： 10.1109/OCEANSE.2017.8084829

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To determine E-field at a tip of probe for evaluating SAR (specific absorption rate) values of DUTs in saline solution, use of near-field transmit antenna factor (NF-TAF) of small dipole antenna is proposed. NF-TAF can be expressed in closed form by assuming hyperbolic sinusoidal current distribution. Also, it can be evaluated by measuring S parameters between two identical dipole antennas and dielectric property of the saline solution. Calculated and measured NF-TAF are compared with each other, and limited range of antenna distance should be used for accurate calibration of E-field probe in the saline solution at 6.78MHz.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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To estimate SAR (specific absorption rate) of the wireless devices operated in HF band, the behavior of the near-field gain in the near-field region of the reference antennas operated in the tissue-equivalent liquid is required. Some asymptotic expansions of the near-field gain of the reference antennas are derived by using an integral form of the transmission coefficient between the antennas and expansion theorem.

DOI： 10.1109/URSIAP-RASC.2016.7601134

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To evaluate specific absorption rate (SAR) of radio devices operated in MHz band, a small loop antenna can be used to calibrate a probe for estimating field intensity in the tissue-equivalent liquid. In our proposed method, field intensity radiated by a small loop antenna can be expressed in terms of its antenna factor in transmitting mode. In this paper, distance property of the antenna factor is analytically derived to determine a fitting curve.

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Other Link： http://dblp.uni-trier.de/db/journals/i-jep/i-jep6.html#journals/i-jep/OkaAYNINSTS16

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© 2015 IEEE. The educational supporting human network outside the university we call as 'The Network of 100 Wise Men' has been constructed by Faculty of Engineering of Niigata University on the process of educational reform activities. We have operated various kinds of practical engineering programs which have been assisted by the engineers of companies and societies. The network members possess the actual experiences of engineering through the processes of their practical R&D activities. And the guidance, lectures, and advice by the network members have made a lot of beneficial contributions to the engineering education for the university students as well as to the faculties of Niigata University. The network is composed of various generations and industrial areas, which is not only based on the alumni organization but on the personal reliance between the faculties and engineers/scientists through their continueing research collaborations. We are convinced that it must be much advantageous for the university students to obtain the practical engineering skills and their ways of thinking by means of the cooperation of the network members.

DOI： 10.1109/ICL.2015.7318017

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To evaluate specific absorption rate (SAR) in HF band using reference antenna method, dielectric-coated and shielded loop antenna operated in the liquid can be used. It is found that the electric and magnetic field intensity in the near-field region of the reference antenna behave like corresponding far-field if the near-field gain have a plateau as a function of the distance from the antenna. To simulate the perimeter of the loop with a plateau in its near-field gain using Richmond's method of moments, the dielectric property of the cylindrically dielectric shell should be well given by using Lichtenecker's logarithmic mixture law if the dielectric shell is made of heat-shrinkable tube.

DOI： 10.1109/IMWS-BIO.2015.7303818

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To calibrate an electric field prove for evaluating specific absorption rate (SAR) of wireless devices operated in the MHz band, we have proposed the use of circular loop antenna immersed in tissue-equivalent liquid. In our proposed method, near-field gain of the loop antenna should be evaluated to estimate the fields radiated by the loop antenna. However, there is a serious problem that its size which can determined as the near-field gain is constant in its neighborhood is much larger than a liquid container as the frequency is lower, for example, at 6.78MHz. In this paper, we focus on estimating antenna factor for transmitting loop antenna and we examine that the distance property of the small circular loop antenna in the liquid can be estimated in its neighborhood with the antenna factor for transmitting loop antenna by using the method of moments.

DOI： 10.1109/CAMA.2015.7428138

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

To evaluate specific absorption rate (SAR) in HF band using reference antenna method, dielectric-coated and shielded loop antenna operated in the liquid can be used. It is found that the electric and magnetic field intensity in the near-field region of the reference antenna behave like corresponding far-field if the near-field gain have a plateau as a function of the distance from the antenna. To simulate the perimeter of the loop with a plateau in its near-field gain using Richmond's method of moments, the dielectric property of the cylindrically dielectric shell should be well given by using Lichtenecker's logarithmic mixture law if the dielectric shell is made of heat-shrinkable tube.

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It is required that specific absorption rate of mobile devices operated in HF band should be evaluated by using a calibrated probe. In this paper, we propose an extension of reference antenna method, which is one of methods for calibrating the probe. As a reference antenna, we examine a circular folded loop antenna immersed in normal saline solution. If its perimeter is well selected, constant near-field gain can be realized in its near field region. And, to reduce its size, the number of folding should be larger. Also, we show the validity of estimated formula for electric field intensity radiated by the reference antenna with its near-field gain.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

A novel method for calibrating the probes used in standard measurement systems to evaluate SAR (specific absorption rate) of the radio equipment operating at frequencies over 3 GHz is proposed. As for the proposed method, the electric-field distribution produced by a waveguide aperture installed in a liquid container is used to calibrate the SAR probe. The field distribution is shown to be the same as that given by a conventional calibration method by analytically deriving a closed-form expression for the field produced by the waveguide aperture with the help of the paraxial approximation. Comparing the approximated and measured distributions reveals that the closed-form expression is valid for the electric-field distribution near the central axis of the aperture. The calibration factor for a commercial SAR probe is evaluated by the proposed method and agrees well with that provided by the manufacturer of the probe.

DOI： 10.1587/transcom.E97.B.2035

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This paper presents measurement techniques to reduce sampling points in Total Radiated Power (TRP) measurement by spherical scanned probes. For the sampling point reduction, this paper presents modified equi-angle to eliminate the effect of metric coefficient and generalized spiral scanning to pick up measured data uniformly. Data reduction rate is discussed by the measurement results. In addition, a partially spherical scanning is presented for the radiation power measurement only.

DOI： 10.1109/CAMA.2014.7003333

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It is known that coupling between balanced and unbalanced modes on AUT (antenna under test), is calculated by using mixed-mode S parameters. In this paper, it is shown that the coupling can approximately be evaluated by proposed one-port measurement with a quadrature hybrid as well as two-port measurement for equivalent network of AUT.

DOI： 10.1109/iWEM.2014.6963640

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A method to evaluate reflection coefficients accurately by using a hybrid coupler and a sliding short is modified to save measurement time. For modified method, a digital phase shifter is used to vary the phase of reference standard. Radiation efficiency based on Wheeler method for a monopole antenna is evaluated by the modified method to confirm the effectiveness of using the digital phase shifter instead of the sliding short.

DOI： 10.1109/iWEM.2014.6963704

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For calibrating electric-field probe to evaluate the value of SAR (specific absorption rate) for devices at a frequency of 30 MHz, a shielded loop antenna is used as a reference antenna. To facilitate curve fitting for the calibration, near-field gain should be constant near the loop. In this paper, it is shown that the circumference of the loop can be selected as the nearfield gain becomes approximately-constant near the loops.

DOI： 10.1109/iWEM.2014.6963641

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A new technique for estimating far-field gain as well as phase center of antennas operated in liquid is numerically demonstrated. It is easily derived that the distance characteristic of near-field gain for antennas operated in the liquid is the same as that in free space. Moreover, another expression for the near-field gain for antennas operated in the liquid that the authors have proposed is proven to be valid by mathematical formulation and numerical simulation.

DOI： 10.1109/iWEM.2014.6963730

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As a reference antenna operated in the tissue-equivalent liquid at 30 MHz, where the wireless communication devices are used in Japan, an insulated circular loop antenna is useful for calibrating the electric field probe for evaluating the SAR (Specific Absorption Rate) of the devices. Its near-field gain and electric field intensity are numerically simulated by the mothods of moment so that the probe can be calibrated by our formulation. Moreover, if the size of the insulated circular loop antenna is well selected, the near-field gain is approximately coincident with the far-field gain extremely in the neighborhood of the antenna and the behavior of the electric field intensity in the extremely near-field region becomes the same as that in the far-field region.

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Modal analysis on dipole antenna using method of moments and characteristic modes is used to evaluate the amount of the excitation for balanced and unbalanced modes. To separate the current on the antenna into the balanced and unbalanced modes, the current distribution is decomposed into even-and odd-symmetrical distribution with respect to reference plane. As a result, the power ratio of the unbalanced to balanced modes can be numerically computed without setting both balanced and unbalanced feed ports on the analytical model.

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An insulated circular loop antenna (ICLA) immersed in tissue-equivalent liquid is one of candidates for reference antenna to calibrate probes which are used to evaluate SAR (specific absorption rate) for mobile communication devices operated in the MHz band. To clarify operation principle of ICLA immersed in the liquid, ICLA fed at a point along the loop is analyzed by the method of moments with characteristic modes. It is found that the pattern is composed by fundamental and second harmonic cosine current distributions. Also, it is found that the fundamental cosine current distribution is dominant in the direction of the central axis to measure the near-field gain of ICLA.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

The educational program by learn-by-doing engineering has been conducted by the grand in aid of MEXT of Japan. The skills and educational factors lie in the practical R&D driven in the company researches. We have attempted to adopt the before-graduation students to the research collaborations among the company engineers.

DOI： 10.1541/ieejfms.133.180

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPANESE SOC DENTAL MATERIALS DEVICES  

Magnetic fields can represent a health problem, especially low frequency electromagnetic fields sometimes induced by electric current in metallic objects worn or used in or on the body (as opposed to high frequency electromagnetic fields that produce heat). Electric toothbrushes are widely used because of their convenience, but the electric motors that power them may produce electromagnetic waves. In this study, we showed that electric toothbrushes generate low frequency (1-2000 Hz) magnetic fields and induce electric current in dental appliances (e.g. orthodontic and prosthetic appliances and dental implants). Current induced by electric toothbrushes might be dependent on the quantity and types of metals used, and the shape of the appliances. Furthermore, these induced currents in dental appliances could impact upon human oral health, producing pain and discomfort.

DOI： 10.4012/dmj.2012-129

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The probe used in the conventional SAR measurement is usually calibrated in a well filled with tissue-equivalent liquid surrounded by a rectangular waveguide and a matching dielectric window in the frequency range from 800 MHz to 3 GHz. However, below 800 MHz, the waveguides are too large to be used for the calibration. Therefore, we have developed another technique of calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by using two-antenna method. In this paper, the calibration system using the reference dipole antennas in the liquid at 450 MHz, 900 MHz and 2450 MHz is presented and far-field gain of the reference antenna and calibration factor of the SAR-probe are measured and compared with those obtained by using the conventional waveguide system.

DOI： 10.1587/transcom.E95.B.60

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Magnetic fields can represent a health problem, especially low frequency electromagnetic fields sometimes induced by electric current in metallic objects worn or used in or on the body (as opposed to high frequency electromagnetic fields that produce heat). Electric toothbrushes are widely used because of their convenience, but the electric motors that power them may produce electromagnetic waves. In this study, we showed that electric toothbrushes generate low frequency (1-2000 Hz) magnetic fields and induce electric current in dental appliances (e.g. orthodontic and prosthetic appliances and dental implants). Current induced by electric toothbrushes might be dependent on the quantity and types of metals used, and the shape of the appliances. Furthermore, these induced currents in dental appliances could impact upon human oral health, producing pain and discomfort.

DOI： 10.4012/dmj.2012-129

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

The probe used in the conventional SAR measurement is usually calibrated in a well filled with tissue-equivalent liquid surrounded by a rectangular waveguide and a matching dielectric window in the frequency range from 800 MHz to 3 GHz. However, below 800 MHz, the waveguides are too large to be used for the calibration. Therefore, we have developed another technique of calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by using two-antenna method. In this paper, the calibration system using the reference dipole antennas in the liquid at 450 MHz, 900 MHz and 2450 MHz is presented and farfield gain of the reference antenna and calibration factor of the SAR-probe are measured and compared with those obtained by using the conventional waveguide system. Copyright © 2012 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transcom.E95.B.60

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Other Link： http://hdl.handle.net/10191/25728

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EIRP measurement in the direction of maximum radiation has not always been valid to estimate the radiated power from radio equipments integrated with antennas, for example, integrated radiator with antennas shaped like the notebook-sized PC. Therefore, it is recommended that total radiated power (TRP) from equipment under test (EUT) should be estimated by integrating measured EIRPs on the whole surface of the unit sphere. In this paper, a conventional and some novel sampling methods for the TRP estimation, which were proposed to reduce the number of measurement points, are examined by using a measured EIRP data set and compared with each other. For a simulated radio equipment shaped like a notebook-sized PC, it is found that the equi-area and generalized spiral points methods are superior to the equi-angle method in terms of reducing the number of the measurement points and orthogonal three planes method is another candidate in terms of saving measurement time unless the pattern radiated from EUT is not so complicated.

DOI： 10.1587/transcom.E94.B.11174

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DOI： 10.4307/jsee.58.5_67

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

A learn-by-doing engineering career education program adopted by MEXT of Japanese Government has been conducted for three years with the assistance of named &ldquo;A network of 100 wise men&rdquo; , which is a novel supporting organization for the students and faculties of Niigata University. The network is composed by the company engineers or social technicians who have rich experiences in the careers of the actual R&D processes. We have confirmed that the practical experiences they possessed on the course of their R&D processed are quite effective for the students to give them the practical engineering education.

DOI： 10.4307/jsee.58.5_67

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We report the results and further problems on what we call the learn-by-doing engineering career education program which has been conducted for three years by the grant-in-aid adapted in 2006 by MEXT of Japanese government. In the paper, we attempt to estimate the processes of the internship programs which were supported by &ldquo;A Network of 100 Wisdom&rdquo; , an organization outside the university. In this year, we have accomplished the construction of three kinds of internship programs, which have been combined one after another. We confirm that we have given the university students strong motivations toward the technical studies through these practical internship programs.

DOI： 10.4307/jsee.57.5_73

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This paper deals with the study program for leading edge technical development and manufacturing in industry, a new trial &ldquo;Technology Week&rdquo; in Faculty of Engineering, Niigata University, Nagasaki University and Toyama University. This trial is organized by one-week exhibition of new products and technology and a technical lecture. Nine &ldquo;Technology Week&rdquo; programs were held from Dec. 2004, and two to three hundred students joined in each lecture. And also, each trial was highly evaluated by students according to the results of the questionnaires, because 95% of attending students would want to join the next plan basically. At last, it is estimated for the effectiveness and discussed the future development of the &ldquo;Technology Week&rdquo; .

DOI： 10.4307/jsee.57.4_42

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Other Link： http://hdl.handle.net/10191/25730

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

As a technique for calibrating electric-field probes used in standardized SAR (Specific Absorption Rate) assessment, we have studied the technique using the His transmission formula in the tissue-equivalent liquid. It is difficult to measure power transmission between two reference antennas in the far-field region due to large attenuation in the liquid. This means that the conventional Friis transmission formula cannot be applied to our measurement so that we developed an extension of this formula that is valid in the near-field region. In this paper, the method of weighted least squares is introduced to reduce the effect of the noise in the measurement system when the gain of the antenna operated in the liquid is determined by the curve-fitting technique. And we examine how to choose the fitting range to reduce the uncertainty of the estimated gain.

DOI： 10.1093/ietcom/e91-b.6.1831

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The SAR-probe is usually calibrated using a rectangular waveguide with a matching dielectric spacer below 3 GHz. However, the probe diameter is comparable with the cross-section area of the waveguide above 3 GHz and it can deteriorate the accuracy of the calibration. Therefore, there is an alternative method for calibrating the SAR-probe
relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by two-antenna method. In this report, we have built a prototype of a calibration system and presented some calibration results of SAR-probe sensitivity using this method in conducting head-equivalent liquid at 2.45GHz.

DOI： 10.1109/APEMC.2008.4559825

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The SAR-probe is usually calibrated using a rectangular waveguide with a matching dielectric spacer below 3 GHz. However, the probe diameter is comparable with the cross-section area of the waveguide above 3 GHz and it can deteriorate the accuracy of the calibration. Therefore, there is an alternative method for calibrating the SAR-probe; relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by two-antenna method. In this report, we have built a prototype of a calibration system and presented some calibration results of SAR-probe sensitivity using this method in conducting head-equivalent liquid at 2.45GHz.

DOI： 10.1109/APEMC.2008.4559825

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DOI： 10.1109/IWAT.2008.4511339

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A technique of measuring the gain of the antenna in the tussue equivalent liquid is required to develop alternative method for calibrating SAR probe with no use of the waveguide system. It is based on an extended Friis transmission formula which is valid in the near-field region of the antenna in the liquid, because the attenuation in the liquid is so large that the measurement in the far-field region is impossible. The near-field gain is defined and expressed by polynomial expansion in terms of inverse of the distance between the antennas. In this paper, two or three terms of the expansion, including the far-field gain in dB, should be selected to obtain good result of the curve fitting. The effect of shifting initial position of the antennas is also discussed.

DOI： 10.1109/APEMC.2008.4559824

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Chirp Pulse Microwave Computed Tomography (CP-MCT) have been applied to a real human body to visualize the physiological- or biochemical- changes in forearm muscles produced by grasping a rubber hall in saline solution bolus. By subtracting the image of the forearm obtained at rest from that of the loaded one, slight variation in the grey level is observed at the muscle region of the forearm. Although the true cause of variation is not identified at the present stage of the study, some possible causes are conceivable. To suggest appropriateness of the assumption, numerical simulation in which some parameter changes are surely reflected to the grey level variation has been attempted in this study.

DOI： 10.1109/EUMC.2008.4751476

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The reflection method is an accurate and simple method for measuring the radiation efficiency of a small antenna. However, it takes too long and has the disadvantage of underestimating the efficiency due to resonance in the cavity formed by the straight waveguide and two sliding shorts. To reduce the measurement time, one sliding short can be fixed while the other one is moved. To improve the accuracy of this technique, we can set the antenna to be measured at the center of the two sliding shorts or at a local anti-node of the standing wave in the waveguide. When one of the sliding shorts is fixed, the measured efficiency becomes negative at certain frequencies. We examine these reductions in efficiency using an equivalent transmission line model for the reflection method. We also derive analytical expressions for the overall efficiency in the above cases and verify new procedures that enable measurements to be performed without any drops in the measured efficiency.

DOI： 10.1093/ietcom/e90-b.9.2394

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In the 300 MHz to 3 GHz range, probes used to measure specific absorption rate (SAR) of mobile communication devices are usually calibrated using a rectangular waveguide filled with tissue-equivalent liquid. Above 3 GHz, however, this conventional calibration can be inaccurate because the diameter of the probe is comparable to the cross-sectional dimension of the waveguide. Therefore, an alternative method of SAR probe calibration based on another principle was needed and has been developed by the authors. In the proposed calibration method, the gain of the reference antenna in the liquid is first evaluated using the two-antenna method based on the Friis transmission formula in the conducting medium. Then the electric field intensity radiated by the reference antenna is related to the output voltage of the SAR probe at a given point in the liquid. However, the fields are significantly reduced in the liquid, and the gain is impossible to calibrate in the far-field region. To overcome this difficulty, the Friis transmission formula in the conducting medium must be extended to the near-field region. Here, we report results of simulations and experiments on estimated gain based on the extended Friis transmission formula, which holds in the near-field region, and test the validity of the new formula.

DOI： 10.1093/ietcom/e90-b.9.2401

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The reflection method is an accurate and simple method for measuring the radiation efficiency of a small antenna. However, it takes too long and has the disadvantage of underestimating the efficiency due to resonance in the cavity formed by the straight waveguide and two sliding shorts. To reduce the measurement time, one sliding short can be fixed while the other one is moved. To improve the accuracy of this technique, we can set the antenna to be measured at the center of the two sliding shorts or at a local anti-node of the standing wave in the waveguide. When one of the sliding shorts is fixed, the measured efficiency becomes negative at certain frequencies. We examine these reductions in efficiency using an equivalent transmission line model for the reflection method. We also derive analytical expressions for the overall efficiency in the above cases and verify new procedures that enable measurements to be performed without any drops in the measured efficiency.

DOI： 10.1093/ietcom/e90-b.9.2394

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Feasibility of a new microwave radar imaging system for early stage breast tumor detection using chirp pulse microwaves was investigated numerically. In the FDTD-based simulation, the basic idea of discriminating tumors from surrounding inhomogeneous breast tissues was verified and the effects of the bandwidth of CP-MBR on the resolution were examined by varying the frequency band from 2 - 3 GHz to 1 - 4 GHz.

DOI： 10.1109/APMC.2007.4554957

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To evaluate the values of the SAR (Specific Absorption Rate) for the mobile communication devices, electric-field probes should be calibrated to relate the field intensity in the tissue equivalent liquid to its output voltages. As a conventional method for 300MHz-3GHz, it can be calibrated in the liquid surrounded by the waveguide and the dielectric spacer. Above 3GHz, the effect of the probe cannot be ignored unless its diameter is smaller than the conventional probe's one. This would lead to deteriorate the uncertainty of the probe calibration. To overcome this difficulty, we have proposed an alternative method based on an extended Friis transmission formula in the conducting medium. In this method, the gain of the reference antenna operated in the liquid is calibrated and then the probe is calibrated in the radiated field of the calibrated antenna in the liquid. However, the measurement in the far-field region can not be realized by using a vector network analyzer, because the dynamic range of the measurement system is limited whereas the electromagnetic wave is rapidly decayed in the liquid. In this paper, we use the signal generator and spectrum analyzer instead of the vector network analyzer to enhance the dynamic range and measure the power transmission in the far-field region. As a result, the measurable range can be enhanced so that the Friis transmission formula including no contribution of the near field can be applied to the measured power transmission to assure our proposed method.

DOI： 10.1109/APMC.2007.4555136

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In microwave imaging of biological objects, array antennas are desired for efficient- and swift-data acquisition. We have fabricated several kinds of dipole array antennas for microwave imaging of a human body by Chirp Pulse microwave Computed Tomography (CP-MCT). Those antennas are consisted of more than 30 small dipole antennas so printed on a dielectric board as to construct a fan beam-type receiving antenna. The problem of such printed antennas is high return loss nature in high loss liquids such as a saline solution. We have tried to reduce the return loss by achieving the impedance matching between the antenna-conductor and surrounding saline solution (high-loss liquid) by covering the conductor with the same dielectric material as the printed dielectric board. The sandwiched dipole antenna works properly as we expected, but mutual coupling effects among adjacent dipole antennas have to be minimized for tomographic imaging. We have solved this problem by covering all the antenna conductors with small- and separate -dielectric substrates. Return loss of the sandwiched dipole antenna was reduced by more than 10dB as compared to conventional printed dipole antennas.

DOI： 10.1109/EUMC.2007.4405190

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ETH FOUNDATION ZURICH  

One of calibration techniques for electric field probes used in the standardized SAR (Specific Absorption Rate) assessment is based on the Friis transmission formula in the far-field region for the conductive medium. In practice, it is difficult to measure power transmission between transmitting and receiving antennas in the far-field region for the liquid used in the SAR assessment because of its large attenuation. To overcome the difficulty, the authors extended the formula taking into account the Fresnel approximation. The extended formula is valid in the Fresnel region of the antennas for the conductive medium. In this paper, the far-field gain of the antennas can be estimated by not only using the extended formula but also considering systematic uncertainty of measuring power transmission. Adding the effect of the measurement uncertainties can make the resulting uncertainty of the gain small, because the measurement uncertainty of the power transmission largely depends on its level so that this behavior can not be ignored in the liquid.

DOI： 10.1109/EMCZUR.2007.4388216

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

When the efficiency of a monopole is measured by determining the radiation efficiency of a small antenna based on a waveguide and a movable short, there are dips at certain frequencies. In this paper, a transmission line model considering the loss in the movable short is introduced and the efficiency dip phenomena are explained. A method for avoiding the dip is presented. When two movable shorts on the left and right inserted into the waveguide are moved, an efficiency dip occurs at the resonant frequency of the cavity. Therefore, the movable range of the two movable shorts that will avoid the efficiency dip is investigated. When one of the movable shorts is fixed at an arbitrary location, there is a dip in the radiation efficiency at a specific frequency. Therefore, it is confirmed that the dip can be avoided by limiting the range of the fixed location of the movable short. (C) 2006 Wiley Periodicals, Inc.

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It is known that both the Wheeler and reflection methods are accurate and simple techniques for measuring radiation efficiency of small antennas. In this paper, the radiation efficiencies based on both methods are simulated by use of the method of moments with wire-gird model. To clarify the frequency shift between simulated and measured efficiencies based on the reflection method, we pay attention to dips observed in the frequency response of the efficiency based on the Wheeler method. Some simulated results are shown to confirm our proposed techniques for avoiding the dips of the efficiency based on the reflection method.

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DOI： 10.20549/jseejaarc.2006.0_26

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DOI： 10.1109/IWAT.2006.1609038

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Chirp Pulse Microwave Computed Tomography (CP-MCT) was developed for visualization of permittivity distribution inside a human body [1, 2]. Tissue characterization using one of the developed CP-MCT systems has been attempted to discriminate tumor tissues from the normal ones. Based on the dependence of temperature, sugar content, acid content and the other quantities on the permittivity value, non-invasive imaging of such physiological or biochemical quantities have also been attempted by using various phantom models of a human body and some real fruits. Now we need a practical model of CP-MCT in order to evaluate the performance in animal experiments. Thus we developed the high-speed model of CP-MCT that shortens the data acquisition time by adopting the fan beam geometry into the scanner. The scanner is consisted of a single transmitting antenna and 39 printed dipole receiving antennas. The newly developed scanner has excellent radiation characteristics even in the lossy bolus saline solution. It takes approximately 2 minutes to collect all projection data. The performance of the system such as a spatial resolution, data acquisition time and so on were evaluated under various measuring conditions to show the usefulness of CP-MCT in animal experiments.

DOI： 10.1109/EUMC.2006.281203

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But for water, the main component of a fruit is sugar. Most of the fruits contain sugar from 8% to 22% by weight at the harvest time. According to our preliminary study, Chirp Pulse Microwave Computed Tomography (CP-MCT) has a possibility of measuring sugar content distribution nondestructively. The capability is verified easily by measuring the sugar solution. However, permittivity of a real fruit is affected by the other parameters such as the minor components of a fruit. We examined the relationship between the gray level of CP-MCT and sugar content measured with a sugar meter by using A Japanese pears and apples. Due to the spherical shape and air-containing feature in the core regions of those fruits, the biggest correlation coefficient is 0.734. To find the higher correlation between them, image restoration by PSF (Point Spread Function) was attempted.

DOI： 10.1109/EUMC.2006.281221

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Other Link： http://hdl.handle.net/10191/8630

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A method is presented for the simultaneous measurement of the absolute gain of antennas in solution and the dielectric properties of the solution. The principle and formulation are based on a modified Friis transmission formula. This three-antenna method is applied to gain measurement of printed dipole antennas in solution, and demonstrated through comparison with calculated results to be an accurate method for the measurement of both antenna gain and solution dielectric properties.

DOI： 10.1093/ietcom/e88-b.6.2268

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

For the safe and effective use of electromagnetic waves, a method for designing construction materials having selective electromagnetic wave absorption is needed. As an example, the characteristics of a stratified construction material consisting of two different low-loss materials (acrylic resin and glass) is evaluated by numerical simulation, and the electromagnetic wave absorption mechanism is determined. Furthermore, a method is developed for designing stratified construction materials to realize electromagnetic wave absorption at a desired frequency.

DOI： 10.1109/TEMC.2004.842105

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：HORIZON HOUSE PUBLICATIONS LTD  

Chirp Pulse Microwave Computed Tomography (CP-MCT) is a modality for microwave imaging of biological objects. By using the high-resolution model, which uses the chirp pulse signal from 2 GHz to 3 GHz, diagnosis of an early stage breast tumor has been attempted mainly by numerical simulation. However, the FDTD-based numerical simulation showed that only diagnostic information provided by the tomographic images was not sufficient for localizing the tumor in the breast fat tissues. This is mainly due to the strong scattering at the surface of the breast and the boundary between the tumor and surrounding fat tissues because of the big difference in those permittivity values. To gain the compensative information, we have investigated feasibilicity of the breast radar, which provides the dosimetric image according to the same measurement principle as CP-MCT. The Chirp Pulse Microwave Breast Radar (CP-MBR) can provide tumor information projected onto the imaging plane of CP-MCT. The numerical simulation of the breast radar shows that the integrated use of those microwave imaging systems is useful for localizing the early stage tumors in the breast.

DOI： 10.1109/EUMC.2005.1610108

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A large absorption of the electromagnetic wave achieves using periodically layered materials with low loss. Our FDTD calculation demonstrates the sharp absorption at discrete frequencies for TM and TE polarizations. These frequencies are called absorbing peak frequencies, which are determined by the characteristic equations related to the transversal resonance in the cross section of the composite material. An equivalent dielectric constant of the composite material is required to solve these equations. One method to estimate the equivalent dielectric constant is based on electrically stored energy in the material, and the other is based on the effective dielectric constant method. The absorbing peak frequencies obtained by two methods are compared with FDTD calculation.

DOI： 10.1109/ISEMC.2005.1513474

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The normalized impedance of a transverse slot on the image plate of an image NRD that is a modification of the original NRD is formulated by means of the method of moments. In terms of the modes that can be supported within the image NRD guide, the electromagnetic field inside the guide is modally expanded and the dyadic Green's function (DGF) is obtained. In addition, by applying the concept of the virtual cavity method, the DGF is modified. The numerical results are compared with the experimental data obtained by the standing wave measurement method. The difference in the resonant frequency is 1.6% and a shift of the peak value is observed. Nevertheless, the tendencies of the frequency locus are identical.

DOI： 10.1002/ecja.1155

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An efficient way of permittivity value estimation in a model-based standing wave method used for measuring a construction material has been investigated. Accuracy of the estimation is slightly improved by using a thin and long piece of material, but essential solution may be given by using a material sample whose size is fully large as compared to the measuring wavelength.

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It is known that EM waves are largely absorbed at discrete frequencies, which we can call absorbing frequencies, when a plane wave is normally incident onto the surface of the stratified structure which consists of two low-loss construction materials. In this paper, an approximate analysis on the absorption will be given and a design formula and a design diagram for the structural parameters will be presented. Furthermore, formulae for the Q-factor concerned with the absorption and the change in the absorbing frequency due to the change of the effective dielectric constant of the composite construction material by the perturbation method will be derived.

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The standing wave method for the spherical wave incidence has been developed to estimate the complex permittivity of construction materials. In this paper, the behavior of spherically standing wave in front of the construction materials has been theoretically analyzed by the use of the spectral domain approach. As a result, the relationship between the complex permittivity and the reflection coefficient at the front surface of the grounded materials is derived, when a spherical wave is irradiated toward the material. This relationship can be expanded for all types of the incident wave including the plane wave incidence. A number of the numerical models for the composite materials have been so simulated by means of the FDTD technique as to check the validity of the relationship.

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A model of the measuring system has been developed to estimate accurately the complex permittivity of construction materials based on the standing wave method in free space. It is assumed in the model that the standing wave distribution is represented by the sum of the incident-, reflected- and scattered-wave components. In this paper, the measurement conditions of the model based measuring method have been discussed by means of computer simulation using FDTD techniques. It has been concluded that the size of the materials should be larger than 600 millimeters square in order to estimate complex permittivity accurately by the model based method.

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A simplified model of permittivity measurement system based on the standing wave method in free space has been developed to estimate complex permittivity of construction materials accurately. It is assumed that the standing wave distribution is determined by three spherical wave components in this model that are the incident-, reflected- and scattered-waves at the edge of the material under test. The model is described by the equation in which the standing wave distribution is represented by the sum of those three wave components. By applying the least squares method to the model equation, the amplitudes and phase angles of those three wave components are estimated from the experimentally observed standing wave distribution. We can estimate the material permittivity from those estimated parameters of the model with high accuracy.

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At millimeter wave frequencies, the loss in the transmission line is significant. To alleviate this problem, a quasi-optical mixer will reduce the transmission loss by combining the antenna and the mixer. The RF and the local signals at two different frequencies are received spatially, and the intermediate frequency is generated immediately. To realize this function, there is a microstrip antenna fed by a coplanar waveguide to operate at two frequencies. In this paper, the spectral domain method is used to analyze the input characteristics of the 1/20 scale model of this antenna at microwave frequencies. It is shown that the antenna can be operated at two frequencies independently. Further, the radiation characteristics of this antenna are evaluated in terms of the absolute gain.

DOI： 10.1002/1520-6424(200103)84:3<21::AID-ECJA3>3.0.CO;2-D

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Problems such as unnecessary absorption of electromagnetic waves, interference between communication devices, information leakage through electromagnetic waves radiated from a computer should be solved by selective use of electromagnetic waves in the living space. This should be realized by developing new construction materials that are able to transmit electromagnetic waves selectively. From economic point of view, such new functional materials should be made of traditional materials by varying the constituents, cross sectional shape, and so on.
Transmission characteristics of a new construction material that has a periodicity in the longitudinal direction have been analyzed by means of FD-TD analysis using a supercomputer. Selective attenuation of electromagnetic waves by the new material would provide a methodology of EMC design.

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So-called time-domain measurement techniques were employed for visualizing the complex permittivity distribution inside a human body. A microwave pulse with a bandwidth from 0.8 GHz to 41 GRz is radiated from a transmitting antenna toward the object immersed in a saline solution that is called a bolus. The transmitted signal is detected by a receiving antenna that is placed on the opposite side of the transmitting antenna. The signal transmitted on the straight path between those two antennas is measured by leaving only the signal that corresponds to the transmission time between those two antennas. This procedure is repeated to obtain a complete set of projection data of the target while the antenna pair is moved on and around the translation- and rotation-axes just like the first generation X-ray CT. The transmission time between two antennas is estimated from complex permittivity of a bolus and biological phantoms. It was demonstrated that time-domain microwave computed tomography (TD-MCT) is feasible by measuring only the transmitted signal on a straight-transmission-path between two antennas by means of a time-domain measurement technique.

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The quasi-optical antenna mixer system transforms an RF signal into an intermediate frequency signal just after it spatially receives the RF signal and the local oscillator's CLO) signal. In this paper, we present a novel beam-scanning system using the quasi-optical antenna mixer array and describe its principle of operation and the experimental results in the microwave band. The arrival direction of RF signals can be controlled by adjusting the LO incident angle and/or the LO frequency without implementing RF circuits such as phase shifters, Therefore, the novel beam-scanning system has no loss due to RF circuits and can be easily designed because of its simple composition.

DOI： 10.1109/8.785747

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Other Link： http://hdl.handle.net/10191/8847

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The quasi-optical antenna mixer system transforms a radio frequency (RF) signal into the intermediate frequency (IF) signal as soon as the system receives the RF and the local oscillator (LO) signals spatially. This system can be expected to reduce transmission line loss, especially in higher frequency bands, such as the millimeter-wave band, because the RF transmission line is removed. In this paper, we propose a dual frequency operating microstrip antenna fed by coplanar waveguide, with a mixer diode to realize the quasi-optical antenna mixer system. It is a problem of the receiving part in conventional quasi-optical antenna mixer systems that LO incidence obstructs RF incidence because both RF and LO signals are received from one side of the system. Therefore, we construct a quasi-optical antenna mixer system that can receive the RF and LO signals separately on both sides of the substrate. To begin with, the receiving part is designed and its characteristics are evaluated with an electromagnetic simulator. Next, the system is fabricated and tested on the dual frequency operation of the receiving part and the mixing operation in the microwave band. As a result, we confirm that our proposed system functions as a quasi-optical antenna mixer. © 1998 Scripta Technica.

DOI： 10.1002/(SICI)1520-6424(199901)82:1<22::AID-ECJA3>3.0.CO;2-M

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The quasi-optical antenna mixer system transforms radio frequency (RF) signal into intermediate frequency (IF) signal just after the system receives the RF and local oscillator's (LO) signal spatially [1]. We present a novel beam scanning system with the quasi-optical antenna-mixer array. In this paper, we describe the principle and the experimental results in the microwave band. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters. Therefore, not only losses in RF circuits are reduced but also the system is easily designed because of its simple structure. This feature is an advantage in applying to the millimeter wave band. © 1998 IEEE.

DOI： 10.1109/EUMA.1998.338025

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Small receivers such as pagers are used in various situations due to their portable nature. These portable units are subject to changes in situation and shift of location so that the receiving gain of arriving wave changes significantly. In this paper, the characteristics of planar loop antennae are studied in detail. We proposed that polarization characteristics can be improved significantly by switching the shorting location of the planar loop antenna. In order to study this effect more realistically, polarization characteristics are measured and evaluated using a model that includes a switching circuit and an oscillator. © 1998 Scripta Technica.

DOI： 10.1002/(SICI)1520-6424(199806)81:6<24::AID-ECJA3>3.0.CO;2-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Small planar-type loop antennas used in pagers have fixed directivity patterns, As a result, the received signal strength depends on the orientation of the antenna. A new type of small planar loop antenna (PLA) is, therefore, proposed, The position of conductor posts can be changed and MOSFET's are adopted for switching the Conductor posts, If the positions of the posts can be switched at will, then the dependence of the received signal on the orientation of the antenna can be minimized, Fundamental experiments were performed in order to investigate the characteristics of polarization switching. Polarization directivity was measured while switching each conductor alternately, The receiving characteristics are affected by a cable connected to the receiver, Therefore, the transmission characteristics are measured by using an internal oscillator. As a result, meaningful results were obtained and the possibility of polarization diversity was shown.

DOI： 10.1109/8.650200

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The antennas for mobile communication handsets have become smaller in shape, which has degraded their electrical performance significantly. To obtain a small but high-performance handset, it is important to increase the antenna efficiency. The important parameter for such a purpose is the radiation efficiency which can be measured easily by the Wheeler method. This method is carried out based on the assumption that the input power is equal to the power loss if the antenna is covered with a cap of a size on the order of a radian sphere. However, unless this assumption holds, the computed Wheeler efficiency does not give accurate radiation efficiency. When the radiation efficiency is actually measured by the Wheeler method, the measured values often have a dip from the theoretical value. In this paper, the cap is approximated by wire grids and the Wheeler method is simulated on a computer. It is confirmed that the dip is not caused by the measurement method. It is shown that the cause derives from the invalidness of the presumption of the Wheeler method that the internal reactive electromagnetic field does not change when a cap is placed. It is shown also that the Wheeler method can be used sufficiently even if the size of the cap is larger than the radian sphere. The limit of application is studied.

DOI： 10.1002/ecja.4410790610

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It is often not possible to operate a microstrip antenna with a probe feed with a zero reactance at the designed frequency because the self‐inductance of the probe is added to the input impedance. It is proposed that by means of matching stubs added on the periphery of the patch, this excess reactance is cancelled. Few examples exist on the analytical studies of the operating principle of such a proposal. In the present paper, it is noticed that this matching stub resembles by shape the metal piece added for separating the degeneracy in the design of a circularly polarized annular microstrip antenna with a one‐point feed. Then the effects of these two metal pieces and the feed pin are analyzed by the eigen function expansion method and the perturbation method. It is found that the excitation amplitude ratio of the two principal modes can be varied and the phase of the input impedance can be controlled by adding the matching stubs. Further, the design of areas and locations of the two metal pieces are investigated for generation of a circular polarization. Copyright © 1995 Wiley Periodicals, Inc., A Wiley Company

DOI： 10.1002/ecja.4410781105

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, we analyze high-T(c) superconducting (HTS) microstrip antenna (MSA) using modified spectral domain moment method. Although it is assumed that the patch and the ground plane of the MSA are perfect electric conductors (PECs) in the conventional spectral domain method, we modify this method to compute the conduction loss of the HTS-MSA. In our analysis, the effect of the HTS film is introduced by the surface impedance which we can estimate by using the three fluid model and experimental results. This paper presents numerical results about the HTS-MSA, for example, the relations between the thickness of the substrate and the radiation efficiency, the temperature and the resonant frequency, and so forth. And we discuss the effective power range where the performance of the HTS-MSA is superior to that of the Cu-MSA.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE - INT SOC OPTICAL ENGINEERING  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

A theoretical and experimental study of a thin card-sized antenna is presented. The method of moment with a wire-grid model is used to analyze this antenna. In order to validate numerical efficiency, measurements using Wheeler method are preformed on this antenna and its wire-grid models. The experimental and theoretical results are in good agreement if the wire conductivity is well chosen. And the noise reduction of measured Wheeler efficiency using least mean square method is also examined.

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In this paper, the characteristics of the card-sized paging antenna composed of plates and wires are estimated in view of its efficiency. To analyze this type of antennas using the reaction matching technique for the wire antenna, we approximate the plate parts to the wire grids. In the analysis of the antenna with a complex configuration, the numerical input impedance by the usual reaction technique assumed the local symmetry in calculating one mutual impedance, is sometimes incorrect. Therefore, we carry out the reaction matching on the condition that the dipoles are placed at their own positions throughout calculating the mutual impedances. In modeling the plate with a wire-grid, we estimate the loss effect of the plate parts by introducing the equivalent radius. Furthermore, we examine the validity of the wire-grid model for the card-sized antenna. And, we estimate the radiation efficiency as a function of the gap distance of the plates, and discuss the polarization matching and the impedance matching of the thin paging antenna, in view of the total efficiency.

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The effective wavelength in the solution, becomes shorter than free space, but it is not able to ignore the loss due to the solution so that the electromagnetic wave cannot be detected before reaching to the distance which satisfies far-field condition. For this reason, it is required to estimate far-field gain from measured S parameters in the near-field region of the antennas. In this paper, some methods for measuring the near-field gain immersed in the solution as well as their theoretical background are described and some experimental results are presented.

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Mixed-mode S parameters can be used to quantitatively the generation of the balanced and unbalanced modes on the asymmetric antennas under test with balanced feed, and can be estimated by measuring conventional S parameters between two ports disposed on the antenna. So far, it has been clarified that S_<dd> and S_<cc> corresponding to the reflection coefficients of the balanced and unbalanced modes, can be evaluated by one-port measurement using a 180° 3dB hybrid coupler. In this report, it is revealed in principle that S_<cd> which corresponds to the coupling coefficient between the balanced and unbalanced modes. can be evaluated by one-port measurement using a 90° 3dB hybrid coupler, for balanced feed antenna such as dipole antennas, folded dipole antennas.

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Wheeler method is known as a simple method of measuring radiation efficiency for small antennas. To reduce uncertainty of measured radiation efficiency, authors have examined a method of measuring reflection coefficients with a 180° 3 dB hybrid coupler. A sliding short can be used to change the phase of the reflection coefficient for reference standard, but it takes a lot of time to measure them because of manually adjusting the position of the sliding short. In this paper, we aim to shorten the measurement time by using a phase shifter and short instead of the sliding short and point out a problem.

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For the reflection method that can measure the radiation efficiency of small antennas using the rectangular waveguide and sliding shorts, a dip of the radiation efficiency is observed when the cavity formed by the wavegude and shorts is resonant. To overcome the difficulty, the reflection coefficient at the cavity resonance should be excluded when evaluating the radiation efficiency. For the antenna system under test with large loss, the reflection coefficients measured draws a circle whose center is off the origin of the Smith chart and radius is smaller than unity when the sliding shorts are moved. So, the detection algorithm for the cavity resonance using the magnitude of the reflection coefficient should be confirmed to be applied to the antenna with large loss. In addition to the above confirmation, we examine a novel detection method to judge that the measured reflection coefficients are on a circle by calculating the cross-ratio.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

It is known that the input impedance of balanced antennas can be measured with the 180-degree 3dB hybrid coupler. However, to accurately measure the input impedance of balanced antennas, it is necessary to consider the S-parameter of 180-degree 3dB hybrid coupler because the S-parameter of 180-degree 3dB hybrid coupler is not ideal. In this paper, we examine and compare the three methods to correct the input impedance. The two methods require full two-port measurement between the sum and difference ports of 180-degree 3dB hybrid coupler, the other method requires only one-port measurement at the difference port. Furthermore, we confirm the effectiveness of the proposed methods to correct the input impedance by comparing with the input impedance calculated by the methods of moment.

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In the standard system of evaluating SAR (specific absorption rate) of radio equipments, a probe is used to measure the electric field intensity in the tissue-equivalent liquid. Since the frequency used for the mobile communication devices being higher, the authors have proposed a novel technique for the probe calibration at the frequency of 5200MHz. We produced our proposed model experimently, which is a waveguide aperture with a dielectric slab entirely inserted into the waveguide for the operation in the liquid. Then, the electrical field intensity radiated from the waveguide aperture was measured and the calibration factor of the probe was determined in comparison with that provided by the probe's manufacturer. The spatical uniformity of the distribution of the electric field intensity produced by the aperture distribution is similar to that of the distribution of the standard field by conventional waveguide calibration method in the vicinity of the waveguide aperture. Therefore, we can apply this novel probe calibration technique with conventional algorithm.

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Several mesurement techniques using 180° 3dB hybrid coupler or power divider were proposed to reduce the uncertainty of measurement of the reflection coefficients. We have proposed how to use sliding shorts as reference standards in these measurement techniques to measure arbitrary reflection coefficients. In addition, these proposed techniques are applied to the measurement of the radiation efficiency based on the Wheeler method for the small antenna, and it is experimentally confirmed that the uncertainties are reduced. On the other hand, it would appear that the uncertainty can be reduced by inserting an attenuator between vector network analyzer and the antenna to make the reflection coefficient smaller than 1. In this report, we discuss the differences of uncertainty of radiation efficiency of the monopole antenna by our proposed techniques.

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Reflection method is known as one of the simple measurement methods for the radiation efficiency of the small antennas. In this method, the radiation efficiency can be estimated by measuring reflection coefficients of the antenna under test (AUT) in free space and the cavity formed by a rectangular waveguide and two sliding shorts. The authors have clarified that the dips in the estimated efficiency could be observed when the distance between the two sliding shorts or between the AUT and a sliding short is equal to half-integer multiple of the wavelength in the waveguide. This fact is derived on the assurnuption of a monopole antenna as AUT. In this paper, we will experimentally assure that the above conditions for avoiding the dips in the radiation efficiency continues to be valid for other configurations such as a rectangular loop and a inverted-F antennas. For example, we will discuss the relatioship between the frequencies at the dips in the radiation efficiency and the direction of the antenna when it inserts in the cavity, and so on. Finally, we will propose a generalized condition for avoiding the dips in the radiation efficiency when applying the reflection method.

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Wheeler and reflection methods are known as simple methods of efficiency measurement for small antennas. They have a serious problem that estimated efficiency is smaller than real efficiency at cavity resonance due to the loss of the cavity wall when an antenna under test is installed into a cavity to suppress the radiation from the antenna. In this report, electric field distribution in a rectangular cavity is depicted when a monopole antenna is installed into the cavity, and some amplitudes of the cavity modes which exist in the cavity are analyzed by using the electric field which can be simulated by method of moments with wire-grid approximation to examine the reason why the efficiency is lower at the cavity resonance.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We focus on a novel calibration technique for an electric-field probe used in the standard evaluation of SAR (specific absorption rate) for mobile communication devices, in which we use the electric field distribution produced by a waveguide aperture operated in the tissue-equivalent liquid. In this report, we analytically derive an approximate expression for the electric field distribution near the waveguide aperture in the homogeneous lossy medium if the aperture is excited by its TE mode. The formulation is validated by measuring the electric-field distribution with a probe scanned in the liquid for the SAR evaluation at the frequency of 5200MHz. Moreover, we can find that measured CF (calibration factor) of the probe in our proposed probe calibration technique is well agreement with the manufacturer-supplied CF.

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The SAR-probe is usually calibrated using a rectangular waveguide with a matching dielectric spacer above 800MHz and below 3GHz. However, below 800MHz, the waveguide is hard to be used for the calibration because the size of waveguide becomes too big. Therefore, we have proposed an alternative method for calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the liquid by two-antenna method. In the previous report, we presented the validity of our calibration method using reference dipole antenna in the head-simulation liquid at 2.45GHz. In this reports, we present that we create the calibration system for 450MHz and result of absolute antenna gain and SAR probe calibration factor. In addition to it, we also create the dipole antenna for 900MHz and 2450MHz and perform the calibration to compare with the calibration factor using a rectangular waveguide.

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DOI： 10.1299/jsmehs.2009.46.153

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In this paper, we evaluate the systematic uncertainty of some evaluation formulas for Wheeler efficiency using the magnitude of the reflection coefficient or the input impedance or the input conductance in free space and radiation shielding, namely, Wheeler cap. The dimension of the Wheeler cap is selected to avoid dips in the Wheeler efficiency in the desired frequency band. However, the efficiency might fall a little near the antenna resonance, when using the evaluation formula with the magnitude of the reflection coefficient. We also evaluate the systematic uncertainty of our proposed evaluation formula to avoid the above slight dips. As sources of overall uncertainty of the Wheeler efficiency, there are the magnitude of the reflection coefficient, input resistance and the input conductance of the antenna under test in free space and the Wheeler cap. By calculating their contribution of the overall uncertainty, we can find that the measurement of the antenna in the Wheeler cap dominates the overall uncertainty. In addition, we can also find that the uncertainty of the Wheeler efficiency slightly varies from formula to formula by comparing four evaluation formulas.

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DOI： 10.20549/jseejaarc.2008.0_434

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DOI： 10.20549/jseejaarc.2008.0_436

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DOI： 10.20549/jseejaarc.2008.0_460

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In microwave imaging of biological objects, array antennas are desired for efficient- and swift-data acquisition. We have fabricated several kinds of dipole array antennas for microwave imaging of a human body by Chirp Pulse Microwave Computed Tomography (CP-MCT). Those antennas are consisted of more than 30 small dipole antennas so printed on a dielectric board as to construct a fan beam-type receiving antenna. The problem of such printed antennas is high return loss nature in high loss liquids such as a saline solution. We have tried to reduce the return loss by achieving the impedance matching between the antenna-conductor and surrounding saline solution (high-loss liquid) by covering the conductor with the same dielectric material as the printed dielectric board. The sandwiched dipole antenna works properly as we expected, but mutual coupling effects among adjacent dipole antennas have to be minimized for tomographic imaging. We have solved this problem by covering all the antenna conductors with small- and separate-dielectric substrates. Return loss of the sandwiched dipole antenna was reduced by more than 10dB as compared to conventional printed dipole antennas.

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Other Link： http://search.jamas.or.jp/link/ui/2008171595

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We are going to detect the breast tumor by using two kinds of microwave imaging systems. One is Chirp Pulse Microwave Computed Tomography (CP-MCT), which is used for tomographic measurement of the breast. Another method is Chirp Pulse Microwave Breast Radar (CP-MBR), which obtains the radar image by radiating the chirp pulse microwave onto the breast. In this study, we assumed that the breast was represented by the three-dimensional hemisphere. Feasibility of tumor detection was examined by means of the FDTD-based simulation. At first, the effects of the bandwidth of CP-MBR on the resolution were examined by varying the frequency band from 2-3GHz to 1-4GHz. In addition, the effects of mammary gland were examined by taking the fibroglandular tissues into consideration in the numerical model.

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The Wheeler method and reflection method are known as accurate and simple methods for measuring the radiation efficiency of small antennas. In these methods, the radiation efficiency can be evaluated by measuring the reflection coefficient of the antenna in free space and in the sheilding cavity or the waveguide with two sliding shorts. However, some dips of the radiation efficiency can be observed because of the cavity formed by the waveguide and two sliding shorts. Especially, the authors have proposed some techniques for avoiding the dips in the reflection method. In this report, we simulate reflection coefficients by the method of moments with the wire-grid model. We consider numerical dips of efficiency, after showing that the simulated results agree with measured ones.

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The reflection method is well known as an accurate and simple measurement method of the radiation efficiency of the antenna. In this method, the radiation efficiency can be evaluated by measuring the reflection coefficient of the antenna in free space and in the waveguide with two sliding shorts. However, some dips of the radiation efficiency can be observed because of the cavity formed by the waveguide and two sliding shorts. In the previous study, we clarified the phenomenon of the dip by using transmission line model. To avoid the dips, we have proposed that two sliding shorts are equally moved. In this case, some small dips can be observed by slight differences of the location of the sliding shorts. The dips are limited in the extremely narrow frequency range. We confirmed the dips of the radiation efficiency by using transmission line model and method of moment. In this paper, we proposed a new technique to avoid these dips by checking the magnitude of the reflection coefficients of the antenna in the cavity.

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We have studied standing-wave method using a point source as a method of measuring the complex permittivity of the construction material. In this report, a simple measurement system was set up and the magnitude of the electric field was measured as a faction of the distance between the material and the receiving antenna. The measured data were fitted to theoretical curve to obtain the reflection coefficient in front of the material. Our proposed method is made valid by comparing the resulting complex permittivity with that measured by probe contact method. Also, the technique for reducing computation time that proposed before is useful for measured wavefront of the electric field produced in front of the material.

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As a technique for calibrating electric-field probes used in standardized SAR (Specific Absorption Rate) assessment, we have studied the technique using the Friis transmission formula in the tissue equivalent liquid. It is difficult to measure power transmission between two reference antennas in far-field region due to large attenuation in the liquid. This means that the conventional Friis transmission formula cannot be applied to our measurement so that we developed an extension of this formula that is valid in Fresnel-field region. In this report, the method of weighted least square is introduced to reduce the contribution of noise in the measurement system when the gain of the antenna in the liquid is determined by curve-fitting. And we examine how to choice the fitting range to reduce the uncertainty of the estimated gain.

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One of calibration techniques for a SAR probe used in the standard SAR measurement is based on the Friis transmission formula. However, the electromagnetic wave is significantly attenuated in the tissue equivalent liquid so that the measurement in the far-field region of the antennas is quite difficult. To overcome the difficulty, the authors extended the Friis transmission formula so as to be valid in the Fresnel region of the antennas. In this report, we clarify that the far-field gain can be estimated by use of only measured data in the Fresnel region. A target function for the curve fitting is Fresnel region gain which converges with the far-field gain in the far-field region. And, the extended gain can easily replace the formula for the electric field intensity radiated by the antenna in the far-field region as that in the Fresnel region.

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DOI： 10.20549/jseejaarc.2007.0_754

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Chirp Pulse Microwave Computed Tomography (CP-MCT) was developed for visualization of permittivity distribution inside a human body [1, 2]. Tissue characterization using the developed CP-MCT systems has been attempted to discriminate tumor tissues from the normal ones. Based on the dependence of temperature, sugar content, acid content and the other quantities on the permittivity value, non-invasive imaging of such physiological or biochemical quantities have also been attempted by using various phantom models of human body. Now we need a practical model of CP-MCT in order to evaluate the performance in animal experiments. Thus we developed the high-speed model of CP-MCT that shortens the data acquisition time by adopting data acquisition in time domain and fan beam geometry into the scanner. The scanner is consisted of a single transmitting antenna and 39 printed dipole receiving antennas. The newly developed array antenna used as the receiving antenna has excellent reflection characteristics even in the lossy bolus saline solution. It takes approximately 2 minutes to collect all projection data.

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The improved Wheeler method is known as an accurate and simple method for measuring the radiation efficiency of a small antenna. Two big problems arise in the measurement of the radiation efficiency using this method, in which a straight waveguide and two sliding shorts are implemented. One is that it takes a long time for the measurement and the other is that the accuracy of the efficiency deteriorates because some dips in the efficiency occur at the resonance of the cavity, which can be formed by the waveguide and shorts. To overcome these problems, we take note of the arrangement of the sliding short in the waveguide. Concretely, to reduce a measurement time, we fix one sliding short, whereas the other sliding short can be moved. To improve the accuracy, we can set an antenna under test at the middle of two sliding shorts, where the magnitude of the standing wave is locally maximized in the waveguide. When a sliding short is fixed, the efficiency falls into negative territory at some frequencies. We theoretically consider the drops using an equivalent transmission line model for the improved Wheeler method. Also, we derive overall efficiency for above two cases and examine the way to measure the efficiency with no drops.

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The SAR probe is often calibrated by use of the waveguide and the matching dielectric slab below 3GHz. However, the diameter of the probe is comparable with the cross section of the waveguide above 3GHz, then it can deteriorate the accuracy of the calibration. Therefore, we propose a new calibration for the probe, in which the output voltage of the probe can be related to the magnitude of the electric field generated by a reference antenna in the liquid. In this calibration, it is necessary to measure the absolute gain of the reference antenna in the liquid and evaluate Type B standard uncertainty. As a consequence of the uncertainty analysis, we can find some sources which deteriorate the uncertainty.

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To estimate the SAR (Specific Absorption Ratio) of the mobile communication device above 3GHz, an alternative method for calibrating the SAR probe is required in place of the conventional calibration using the waveguide system and has been developed by the authors. In our calibration, a reference antenna whose gain is calibrated is immersed in the liquid, and then the electric field intensity radiated from the antenna is related to the output voltage of the SAR probe on the basis of the Friis transmission equation. However, the electric field is significantly attenuated in the liquid and it is difficult to calibrate the antenna gain in the far-field region, where the Friis transmission equation is valid. To overcome the difficulty, we try to use the modified Friis transmission equation in the near-field region, where one antenna can receive the signal from the other antenna in the liquid. In this paper, we show some results of estimating the antenna gain from the near-field data and check the validity of the modified Friis transmission equation.

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The SAR probe is usually calibrated by a rectangular waveguide with a matching dielectric spacer below 3GHz. However, the probe diameter is comparable with the cross-section of the waveguide above 3GHz and it can deteriorate the accuracy of the calibration. Therefore, we propose an alternative method for calibrating the SAR probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the liquid by two-antenna method. Before calibrating the probe, we must calibrate the gain of the reference antenna. To improve the accuracy, we consider the transmission S_<21> between two antennas as a function of their distance, and apply the curve fitting technique to measured S_<21>. In this report, we show measured results of absolute gain in tissue equivalent liquid by two-antenna method and least square method.

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Diffracted waves are superposed on the standing wave in front of the grounded construction material with finite size, if the dimensions are not compared to the wavelength. To solve the above problem, we propose the model-based standing wave method, in which the diffracted waves are excluded in the standing wave by fitting the practical field distribution to the model with the incident, reflected and diffracted waves. However, there is a drawback of time-consuming estimation in this method. In this paper, we propose the preprocessing for the estimation according to the fact that the diffracted waves can hardly exist extremely in front of the material. This preprocessing contributes to saving the time for fitting.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We developed a method for permittivity measurement of construction materials using the model of the measuring system based on the standing wave method in free space. Both of the usefulness and its limitations have been investigated so far by means of the experiments and numerical simulations. In those studies, a complete free space was assumed in the simulation and the experimental condition was almost the same as one in an anechoic room. For practical application of this method, possibility of more simplified measuring condition has been investigated in this study.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The SAR probe is often calibrated by use of the waveguide and the matching dielectric slab below 3GHz. However, the diameter of the the probe is comparable with the cross section of the waveguide above 3GHz, then it can deteriorate the accuracy of the calibration. Therefore, we propose a new calibration for the probe by relating the output voltage of the probe and the magnitude of the electric field generated by a reference antenna in the liquid. We apply the least square method to the curve of the magnitude of S_<21> as a function of the distance between antennas to improve the accuracy of the calibration. In this report, we introduce the principle of the proposed calibration, and discuss the limitation of the new calibration by the method of moment, assumed that an half-wavelength dipole is used as the reference antenna.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

When we measure the radiation efficiency of the monopole antenna by the improved Wheeler method which use the waveguide and sliding shorts, we can observe some dips of the efficiency at discrete frequencies. In this report, we introduce a simple transmission line model including the loss of the sliding shorts, analyze the dips of the efficiency, and then propose some techniques for removing the dips.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Article

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Article

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

A prototype of the 900MHz SAR probe calibration system using waveguide in compliance with ARIB standard has been made to investigate the electrical properties including E-field distribution in the phantom liquid and to acquire decay characteristics and axial isotropy data for SAR probes in the liquid. The decay characteristics is used to derive the conversion factors and the liquid conductivities which is found to be important for SAR measurement. The standard uncertainty for the calibration system is also evaluated following the procedures of the ARIB and IEEE standards.

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Language：English   Publisher：HORIZON HOUSE PUBLICATIONS LTD  

Originally, Chirp Pulse Microwave Computed Tomography (CP-MCT) was developed for noninvasive imaging of a human body. The tomographic image provides not only the permittivity distribution of the cross section but also various physical- or chemical-quantities relating to the permittivity value such as temperature and salt concentration. Generally speaking, fruits are dielectric materials containing much water, sugar, acids and so on. Accordingly, the quantities which vary the permittivity value such as sugar content, acid content and etceteras are visualized by microwave imaging. By use of the high-resolution model of CP-MCT using the chirp pulse microwave signal from 2 GHz to 3 GHz, nondestructive imaging of sugar content inside fruits is worthy to be investigated. In this study, we have confirmed that the sugar distribution inside the Japanese pairs vary according to the harvest time.

DOI： 10.1109/EUMC.2005.1610193

Web of Science

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In measuring the radiation efficiency of the monopole using the improved Wheeler method, some dips of the measured efficiency are observed at discrete frequencies. In this report, the dips can be removed by limiting the moving range of sliding shorts in the waveguide so that a continous measurement of the efficiency can be achieved for the wide frequency range, which is the same as the recommanded frequency range of the waveguide. If both sliding shorts at the ends of the waveguide are possible to be moved, the dips occur at the resonant frequencies of the cavity which is formed by the wavegude and two shorts. The moving range of the sliding shorts is discussed to remove the dips from the efficiency. And, if one of the sliding shorts is fixed and the other is possible to be moved, the dips of the efficiency occur at the frequency of the resonance between the monopole and the fixed short and can be removed by locating the fixed short in the limited range.

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We clarify that large electromagnetic wave absorption occurs at discrete frequencies in the composite material in which two low loss construction materials are layered periodically. In our report, we show that the absorption can be observed for TE polarization as well as TM polarization by means of FDTD calculation, and derive characteristic equations to determine absorbing peak frequencies for both polarization by the use of analytical approach based on our interpretation of the absorption. And we give consideration to the equivalent dielectric constant of the composite material in the view of electrostatic energy. Moreover the effective dielectric constant method (EDC method) is adopted to determine the absorbing peak frequencies of the composite material with higher accuracy.