Kunio Sawaya

Optimization of Block Size for CBFM in MoM

The optimum number of blocks of the CBFM is derived theoretically and demonstrated numerically. The minimum order of CPU time for the CBFM is shown to be O(N7/3) , where N is the number of unknowns. In addition, the optimum size of overlapping region of the blocks also is investigated numerically.

Experimental Investigation of MIMO Performance Using Passive Repeater in Multipath Environment

A passive repeater (PR), comprising a four-element folded-patch antenna (FPA) array, a planar Yagi-Uda antenna, and a power combiner, was fabricated to experimentally investigate the multiple-input-multiple-output (MIMO) performance in multipath environment. It was found that the PR could realize polarization transition and broad-angle scattering. The received power and the MIMO channel capacity, which reflect MIMO performance, were discussed to demonstrate the effectiveness of the four-unit PR in improving the propagation channel in MIMO communications. It was found that the medians of the received power of Rx1 and Rx2 were improved by about 17 dB as compared to those without the PR. Also, when the received noise level was supposed to be -120 dBm/Hz, the median of the MIMO channel capacity with the PR was increased by 6.4 bps/Hz as compared to that without the PR.

Experimental investigation of elimination blindness propagation channel using reflectarray

A 42 × 44-element reflectarray using interdigital gap loading structure element is used as a passive reflector for elimination blindness propagation channel. The proposed reflectarray is designed with a 58-degree scattering angle and fabricated to experimentally investigate the performance and effectiveness in improvement of the receiving signal noise ratio (SNR) and channel quality. It was found that the received power level were improved by more than 12 dB for cumulative distribution function (CDF) at 1% as compared to those without the reflectarray in the none-line-of-sight (NLOS) environment.

DUAL-ANTENNA SYSTEM COMPOSED OF PATCH ARRAY AND PLANAR YAGI ANTENNA FOR ELIMINATION OF BLINDNESS IN CELLULAR MOBILE COMMUNICATIONS

For a cellular mobile communication system in narrow streets of urban areas, blind spots caused by shadowing of high buildings are a signiflcant problem. In this research, a new dual- antenna system (DAS) is proposed, including a power transmission network, a receiving and a reradiating antenna to realize a broad- angle beam control. An equivalent bi-static radar cross section (BRCS) is deduced to present a theoretical explanation to the operating principles of the DAS. The main advantage of this design over ordinary re∞ectarray antenna as a passive RF booster is its ∞exible beam control capabilities. The simulated BRCS of the proposed DAS, composed

Amplitude controlled reflectarray using non-uniform FSS reflection plane

A novel concept using non-uniform frequency selective surface (FSS) backed as a reflection plane for amplitude controlled reflectarray is proposed. First, a modified square-loop FSS element with broad reflection response band (from −22dB to 0dB) is designed. Then, a non-uniform FSS using the modified square-loop element is backed as a reflection plane for reflectarray. By properly controlling each element size of the FSS, the reflection amplitude from the reflectarray element can be sufficiently controlled and amplitude controlled reflectarray can be realized. A reflectarray using Dolph-Tschebyscheff weighting coefficients is implemented and a major-lobe to sidelobe ratios of up to 22 dB is obtained.

Forward-nulling passive millimeter wave imaging using cooling dielectric tube

In order to improve the quality of object recognition characteristics in passive millimeter-wave (PMMW) imaging, a new method to form a null in the direction of human body and objects is proposed. The forward-nulling passive millimeter-wave imaging using a dielectric tube occupied by cooling water placed on focus line of a parabolic cylinder are performed. It is shown experimentally that the contrast between human body and conducting scatterers such as a conducting plate and a conducting sphere in the PMMW images is improved by the presence of cooling dielectric tube with parabolic cylinder.

Analysis of linear antenna near dielectric object by CBFM

Dipole antenna in the vicinity of dielectric object is analyzed by characteristic basis function method (CBFM). Accuracy of numerical analysis is investigated by using different block division for the antenna and dielectric object. It is shown that all antenna segments should be allocated in the same block for calculating input reactance accurately. In addition, it is demonstrated that polarization current in the vicinity of the dipole antenna must be allocated in the block including antenna segments.

A UWB through-wall radar using beam scanning array antenna

A UWB through-wall radar using novel beam scanning array antenna previously proposed by the authors is described. This antenna scanning system has two new technologies. First, each antenna element is equipped with an impulse generator. Second, the time control between the antenna elements is realized by using tapped delay lines and by transmitting trigger signals. Based upon above technology, experimental UWB through-wall radar having beam scanning capability is designed and constructed. The fabricated radar has compact size and light weight and is easy to use. The measurement results show excellent space resolution as a through-wall radar.

Hybrid approach of SPM and matrix-inversion to estimate current distribution of electromagnetic radiation source

A hybrid approach using the sampled pattern matching (SPM) method and matrix inversion is utilized to estimate current distribution of electromagnetic radiation sources with multi-mode current distribution. The current distribution of a loop antenna is detected as an example. The capability of the hybrid method in handling practical problems is demonstrated by estimating the amplitude and phase of electric current sources.

Planar dual-antenna system for blind spots elimination in mobile communication system

A planar dual-antenna system (DAS), composed of series-fed microstrip antenna and planar Yagi-Uda antenna, is proposed for blind spots elimination in mobile communication system. The planar DAS is developed as a reflector in a non-line-of-sight (NLOS) environment. Broad-angle scattering and polarization transition can be realized. Equivalent bi-static radar cross section (BRCS) is used to demonstrate the effectiveness of the DAS in eliminating blindness and improving the propagation channel under the NLOS environment.