Kiyohiko Itoh

Superresolution techniques for time-domain measurements with a network analyzer

Superresolution techniques for time delay estimation are proposed and applied to frequency-domain data measured with a network analyzer. A MUSIC (multiple signal classification) algorithm preprocessed by spatial smoothing is used. The spatial smoothing preprocessing is performed to destroy signal coherence, and the decorrelation performance is examined in detail. The expression which gives an individual response is given. Using this expression, it is possible to eliminate unwanted signals that appear as ripples in the frequency domain. Experimental results show that the frequency bandwidth required by the MUSIC algorithm to resolve distinct time-domain responses and eliminate unwanted signals is much narrower than that required by the FFT (fast Fourier transform). Thus, the MUSIC algorithm is applicable to the time-domain measurements with the network analyzer and has much higher resolution capability than the conventional FFT techniques. The MUSIC algorithm is one of the most promising methods of enhancing the accuracy of measurement for narrowband devices such as antennas. >

A study on a channel allocation scheme with an adaptive array in SDMA

This paper describes spatial division multiple access (SDMA) using an adaptive array. A spatial correlation coefficient is proposed as a criterion to determine the possibility of duplicate channel allocation. When the average input SNR is more than 20 dB, the users satisfying a correlation coefficient of less than 0.9 can be accommodated in the same channel in a 2-user SDMA model with a 2-element adaptive array. The blocking rate performance shows that this 2-user SDMA can improve channel efficiency almost twice.

An LMS Adaptive Array for Multipath Fading Reduction

Multipath fading often poses a serious hindrance in radiocommunication. The application of a least-mean-square (LMS)adaptive array to the problem of multipath fading reduction is discussed. However, it is known that multipath components are in general correlated with one another. We examine the effect of the correlation on the performance of the LMS adaptive array. When the correlation coefficient does not equal or approximate 1, the LMS adaptive array suppresses the multipath signals significantly by nulling. On the other hand, when the correlation coefficient nearly equals 1, the LMS adaptive array prevents the output signalpower from decreasing. Therefore, the LMS adaptive array mayreduce the multipath fading effectively for any correlation coefficient value. A reference signal in the LMS adaptive array is also discussed. It is shown that synchronization in the referencesignal generation must be extremely accurate. Moreover, aprocessor configuration is proposed which may generate thereference signal with the required accuracy.

Considerations on performance evaluation of cavity-backed slot antenna using the FDTD technique

The finite-difference time-domain (FDTD) method is considered a versatile and efficient tool for the solution of Maxwells equations in complex structures for any time dependence. We show an antenna feed model suitable for performance evaluation of a cavity-backed slot antenna using the FDTD technique. The gap voltage and the coaxial feed models are examined, and their input characteristics and absolute gains are compared. Analytical results show that the input characteristics are estimated with fewer time steps for the coaxial model than for the conventional gap voltage model. Furthermore, we show how to calculate absolute gains and radiation patterns using the coaxial model and a sinusoidal voltage source at the desired frequency. The computed results of the absolute gain converge after the fifteenth period of the voltage source for the coaxial model and are in good agreement with the experimental results. On the other hand, the absolute gain is observed to fluctuate when the gap voltage model is used. The performance evaluation and comparison reveals that the coaxial model is an appropriate feed model for use in the analysis of the performance of the cavity-backed slot antenna using the FDTD technique. The good agreement of the FDTD results with the experimental measurements demonstrates the effectiveness of the model and the method proposed.

Slot-monopole antenna system for energy-density reception at UHF

A new type of energy-density antenna is proposed for mobile telephony in the 800-1200-MHz range using a slot-monopole antenna (SMA) configuration. To mount the antenna on a mobile two orthogonally crossed slot antennas backed by a shallow cavity placed on the roof were found to be most suitable for receiving the magnetic field components, whereas a monopole attached to the base of the cavity and designed as a sleeve antenna is utilized to probe the electric field component. A prototype of the SMA system is manufactured, and its dimensions and design characteristics are presented. The radiation pattern, the input impedance of each of the three sections of the antenna system, and the isolation characteristics between all the sections of the SMA are measured and discussed.

Beam scan using the quasi-optical antenna mixer array

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 oscillators (LO) 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.

An adaptive antenna for spatial-domain path-diversity

High-speed TDMA mobile communications suffer from frequency-selective fading due to multipath propagation. Also, the energy per bit is lower because the symbol duration is short. We need a scheme which reduces the frequency-selective fading and utilizes transmitted power efficiently. This paper presents a new configuration of an adaptive antenna for path-diversity in high-speed mobile communications. The adaptive antenna has several weight vectors which resolve multipath signals in the spatial-domain. The resolved multipath signals are combined equalizing the delay difference. Thus, the frequency-selective fading is suppressed and we can utilize the signal power efficiently. We carried out computer simulations under several scenarios. It is shown that the proposed adaptive antenna reveals a good path-diversity performance.

Slot antenna consisted of two conductive plates and thin wires

The solar power satellite (SPS) was proposed as a sustainable and reusable energy source for mankind in future. This paper discusses a design method of antenna elements whose conductive sidewalls in the conventional model are replaced by thin wires. Such a new configuration makes it easy to produce low profile antenna elements as well as array antennas. Relations between the wire intervals and input characteristics are clarified. It is shown from the study that the method is also available to design the new type of antenna element. This paper describes the geometries of a conventional and a new type of cavity-backed slot antenna, and shows the antenna parameters that realize the impedance matching by using the proposed method. The effectiveness of the design is clarified from computed results. Moreover, the mutual coupling of a nine-element array antenna is considered.

Performance evaluation of cavity-backed slot antennas using the FDTD technique

This paper proposed feed models appropriate for the FDTD evaluation of the input characteristics of the cavity-backed slot antenna. By employing the coaxial model and the gap voltage model, we showed the coaxial model effectively reduced the amount of time steps and did not require the time window function to estimate experimental results of the input characteristics. Compared with the gap voltage model, the coaxial model gives a good estimation of the input impedance by only 3000 time steps. On the other hand, the gap voltage model and time windows required 32768 or 20000 time steps for the accurate estimation. It is concluded that the coaxial model requires only 9 % or 15 % of the time steps required for the gap voltage model. As a result, we concluded the coaxial model is effective for the FDTD analysis of the cavity-backed slot antenna. This technique is easily applicable to the evaluation of mutual coupling and beam steering performance of phased array antennas.

A technique for determining the normalized impedance of slots in the image plane of the image NRDG

This paper presents a method for determining the normalized impedance of a transverse slot in the image plane of the image nonradiative dielectric guide using measurements of the standing wave. The method overcomes the problem of distortion caused by the scattered evanescent fields that are present in the vicinity of the slot. The measurement equipment, its optimum parameters, and aspects necessary for accurate measurements are also discussed. Moreover, the finite-difference time-domain technique is employed to determine the normalized slot impedance, and good agreement is obtained with measured results, confirming the reliability of the method.