In this paper, the influence of surface waves on the characteristics of on-glass antennas is clarified to enable appropriates design of C-band automotive on-glass antennas. Composite glasses are used in automotive windshields. These automotive composite glasses are composed of three layers. First, the surface wave properties of composite glass are investigated. Next, the effects of surface waves on the reflection coefficient characteristics of on-glass antennas are investigated. Finally, the antenna placement to reduce surface wave effect will be presented. Electromagnetic field analysis of a dipole antenna placed at the center of a 300mm × 300mm square flat composite glass showed that the electric field strength in the glass had ripples with the half wavelength period of the surface waves. Therefore, it was confirmed that standing waves are generated because of these surface waves. In addition, it is confirmed that ripples occur in the reflection coefficient at frequencies. Glass size is divisible by each of those guide wavelengths. Furthermore, it was clarified that the reflection coefficient fluctuates with respect to the distance between the antenna and a metal frame, which is attached to the end face in the direction perpendicular to the thickness of the glass because of the influence of standing waves caused by the surface waves; additionally, the reflection coefficient gets worse when the distance between the antenna and the metal frame is an integral multiple of one half wavelength. A similar tendency was observed in an electric field analysis using a model that was shaped like the actual windshield shape. Because radiation patterns also change as a result of the influence of surface waves and metal frames, the results imply that it is necessary to consider the actual device size and the metal frames when designing automotive on-glass antennas.

It is well known that the power transfer efficiency (PTE) of a wireless power transfer (WPT) system is maximized at a specific coupling coefficient under the fixed system parameters. For an adaptive WPT system, various attempts have been made to achieve the maximum PTE by changing the system parameters. Applying the input matching networks to the WPT system is one of the most popular implementation methods to change the source impedance and improve the PTE. In this paper, we derive the optimum source condition for the given load and the achievable maximum PTE under the optimum source condition in a closed-form. Furthermore, we propose a method to estimate the input impedance, without feedback information, and an input matching network structure that transforms the source impedance into the optimum source obtained from the estimated input impedance. The proposed technique is successfully implemented at a resonant frequency of 13.56MHz. The experimental results are in close agreement with the theoretical achievable maximum PTE and show that the use of only a single matching network can sufficiently achieve a PTE close to the ideal maximum PTE.

This paper presents a meta-structured circular polarized array antenna with wide scan angle. In order to widen the scanning angle of array antennas, this paper investigates unit antenna beamwidth and the coupling effects between array elements, both of which directly affect the steering performance. As a result, the optimal array distance, the mode configuration, and the antenna structure are elucidated. By using the features of the miniaturized mu-zero resonance (MZR) antenna, it is possible to design the antenna at optimum array distance for wide beamwidth. In addition, by modifying via position and gap configuration of the antenna, it is possible to optimize the mode configuration for optimal isolation. Finally, the 3dB steerable angle of 66° is successfully demonstrated using a 1x8 MZR CP antenna array without any additional decoupling structure. The measured beam patterns at a scan angle of 0°, 22°, 44°, and 66°agree well with the simulated beam patterns.

The most commonly used scattering parameters (S parameters) are normalized to a real reference resistance, typically 50Ω. In some cases, the use of S parameters normalized to some complex reference impedance is essential or convenient. But there are different definitions of complex-referenced S parameters that are incompatible with each other and serve different purposes. To make matters worse, different simulators implement different ones and which ones are implemented is rarely properly documented. What are possible scenarios in which using the right one matters? This tutorial-style paper is meant as an informal and not overly technical exposition of some such confusing aspects of S parameters, for those who have a basic familiarity with the ordinary, real-referenced S parameters.

This paper presents a spatial division (SD) transmission method based on two-ray fading that dispenses with the high signal processing cost of multiple-input and multiple-output (MIMO) detection and antennas with narrow beamwidth. We show the optimum array geometries as functions of the transmission distance for providing a concrete array design method. Moreover, we clarify achievable channel capacity considering reflection coefficients that depend on the polarization, incident angle, and dielectric constant. When the ground surface is conductive, for two- and three-element arrays, channel capacity is doubled and tripled, respectively, over that of free space propagation. We also clarify the application limit of this method for a dielectric ground by analyzing the channel capacity's dependency on the dielectric constant. With this method, increased channel capacity by SD transmission can be obtained merely by placing antennas of wireless transceiver sets that have only SISO (single-input and single-output) capability in a two-ray propagation environment. By using formulations presented in this paper for the first time and adding discussions on the adoption of polarization multiplexing, we clarify antenna geometries of SD transmission systems using polarization multiplexing for up to six streams.

This paper focuses on the S-parameter method that is a basic method for measuring the input impedance of balanced-fed antennas. The basic concept of the method is summarized using the two-port network, and it is shown that the method can be enhanced to the unbalanced antennas using a formulation based on incident and reflected waves. The compensation method that eliminates the influence of a measurement jig and the application of the S-parameter method for the measurement of a radiation pattern with reduced unbalanced currents are explained. Further, application of the method for measuring the reflection and coupling coefficients of multiple antennas is introduced. The measured results of the input impedance of a dipole antenna, radiation patterns of a helical antenna on a small housing, and S-parameters of multiple antennas on a small housing are examined, and the measured results obtained with the S-parameter method are verified.

This paper proposes a method of designing EM absorber panels under oblique incident waves. TM and TE wave reflection characteristics of the absorber panel show its anisotropy under oblique incidence. By using the wire array sheet proposed this paper, TM and TE reflection coefficients in oblique incidence can be matched at almost the same frequency range.

In this paper, an evaluation method for electromagnetic wave absorber with anisotropic reflection properties is discussed. Anisotropic absorber panels have an axis of anisotropy (principal axis). In order to specify the principal axis, the evaluation method based on the diagonalization of reflection coefficient matrix is used. Also, the permittivity of absorber materials is considered.

The effect of wall and indoor scatterers on the indoor multiple input multiple output (MIMO) communication system is investigated by using the hybrid technique of finite difference time domain (FDTD) method and method of moments (MoM). MIMO channel capacity with the wall reflection is investigated with consideration of the eigenvalue of channel covariance matrix, the received power and the effective multipaths of MIMO system. It is found that the stronger side wall reflection can lead to the higher MIMO channel capacity. MIMO system with indoor scatterers is also analyzed and compared with the line of sight (LOS) indoor MIMO system. It is found that the scatterer material has different effect on the received power and the effective multipaths of MIMO system.

The effects of wall reflection on indoor MIMO channel capacity are statistically investigated with consideration of the average received power, the effective degrees of freedom (EDOF) of multipaths and the eigenvalues of transfer channel covariance matrix. It is found that the stronger wall reflection can lead to higher MIMO channel capacity.

Based on the concept of Equivalent Transformation Method of Material Constant (ETMMC), a thin and light weight EM-wave absorber is newly proposed. It becomes possible to merge both the competing characteristics of changing the matching frequency toward a higher frequency region by means of punching out small holes in the magnetic absorber and of changing the matching frequency toward a lower frequency region by attaching periodical conductive patterns to the surface of it. First, the ETMMC idea is introduced in this paper. The detailed matching characteristics of the present absorber are investigated based on FDTD analysis. The matching mechanism is clarified from input admittance chart viewpoints. The matching characteristics can be changed from 2.4 GHz to above 6.0 GHz using carbonyl iron with the thickness of 2 mm and improved below -20 dB.

A novel method for measuring microwave reflection coefficients without the open and load standards is proposed. In this method, a single probe is inserted into an air line and the output wave is detected by a vector detector. Offset shorts are used for the calibration. The measurement system is constructed using 7 mm coaxial line and APC7 connectors. The result of the measurement in the frequency range 1-9 GHz shows the possibility of the proposed method. All the major systematic errors can be estimated from the data that is easily obtainable.

Development of non-invasive techniques to measure blood sugar level is strongly required. The application of millimeter waves has a great potentiality to realize the measuring technique. Nevertheless, the practical method of the technique is not yet reported. In this paper, a new technique is proposed to measure blood sugar level using millimeter waves. The technique proposed here is very rapid and safety way to obtain blood sugar level.

The fields in the junctions between straight and curved rectangular waveguides are analyzed by using the method of separating variables. This method was succeeded because the authors developed the method of numerical calculation of the cylindrical functions of complex order. As a result, we numerically calculate the reflection and transmission coefficients in the junctions in various situations, and we compare these results with the results by the perturbation method and with the results by Jui-Pang et al.

A new method for measuring the scattering coefficient using a metal-plate reflector was developed in order to provide a non-destructive way for the assessment of microwave materials in free space. By displacing the position of the metal-plate reflector on the specimen to be tested, the incident wave and the scattered wave from the measured area were determined without the influence of extraneous waves such as the direct coupling between transmitting and receiving antennas and scattered waves from background objects. Because the behavior of a metal-plate reflector is similar to that of an optical shutter in optics, our new scattering measurement system enables us to measure both backward- and forward-scattering coefficients of small regions of the specimen for various types of materials in a non-destructive manner. Our study examined the metal-plate size dependence of the complex reflection and transmission coefficients of some dielectric sheet samples. The measured data indicated that the reflection and transmission coefficients of a Bakelite flat plate and Styrofoam sheet were constant for various sizes of metal plates at the X-band.

In this paper, a new simulation approach to the analysis of the reflection characteristics on nonuniform transmission lines (NTLs) is presented. The input and output responses in the time domain and the reflection coefficients in the frequency domain are effectively obtained by using the modified central difference (MCD) simulation and the fast Fourier transform (FFT) technique for Gaussian pulse responses. The simulated results for the reflection characteristics of the NTL transformers are in excellent agreements with the theoretical values. By representing both the reflected voltage and the reflection coefficient, it is shown that this approach is useful to analyze for various types of tapered and stepped NTLs.

Characterization of a mitered, a squarely cut, and a circular E-plane bend in rectangular waveguide is implemented by combining the port reflection coefficient method and the mode-matching method. Based on the port reflection coefficient method, the two-port waveguide bend is converted to a one-port structure comprised of cascaded waveguide step-junctions. After solving the reflection coefficient caused by these waveguide step-junctions using the mode-matching method, the desired scattering parameters of the bend are obtained readily. Convergence properties of the calculated numerical results are validated. Influences of the mitered, the squarely cut, and the circular part of the bend on the scattering parameters are investigated, and the optimal design dimensions for realizing wide-band and low return loss bends are found. Based on the optimal compensation dimension, an E-plane waveguide circular bend is fabricated and tested. The measured result agrees well with the theoretical prediction, and a full-band matched bend is practically realized.

An efficient full-wave approach for the accurate characterization of a H-plane waveguide π-junction with an inductive post and a waveguide cross-junction is proposed. By employing the port reflection coefficient method (PRCM), the analysis and solution procedures of these complex waveguide junctions are greatly simplified and only the calculation of field reflections caused by the simplest waveguide step-junction discontinuities are required. The reflections are easily determined by the mode-matching technique. Scattering parameters of these junctions are provided and discussed in terms of the working frequency and the geometrical dimensions of the junctions. Calculated results are compared with those of other papers and measurements, all show good agreement.

In this paper, mutual coupling S21 between RMSA (ring-shaped microstrip antenna) elements was estimated by the EMF method based on the cavity model. Then, the validity of the proposed method was tested by experiments. The experiments confirmed satisfactory agreement between the computed and experimental data for S21 in both E- and H-plane arrangements. In addition, a circularly polarized planar array composed of R-MSA elements was designed on the basis of the data of S21. The experimental results of such a planar array demonstrated high performance in radiation pattern as well as axial ratio property. Furthermore, the active reflection coefficient Γ in the R-MSA array was also investigated in both equilateral and square arrangements. The computed results of active reflection coefficient in the array demonstrated high performance in both arrangements.

The scattering characteristics of a waveguide T-junction with an inductive post are analyzed by the port reflection coefficient method (PRCM), combined with the mode-matching technique. Variation behaviors of the scattering parameters are provided as a function of the operating frequency and the dimensions of the junction. The results are helpful for the design of power dividers using this type of T-junction configuration.