Yonehiko Sunahara

An annular-ring microstrip antenna fed by a co-planar feed circuit for mobile satellite communication use

A new configuration of circularly polarized annular-ring microstrip antenna (ARMSA) fed by a branch-line hybrid coupler placed at the inner part of the ARMSA and its design method using an equivalent circuit are presented. Since the ARMSA has a narrow bandwidth and high-input impedance, a parasitic element placed above the ARMSA is employed for not only obtaining a broadband characteristic, but decreasing the input impedance down to 50 /spl Omega/. A hybrid coupler to generate circular polarization, therefore, can be connected to the co-planar space of the ARMSA directly without a large-size matching circuit and a very low profile and simple structure can be achieved. The ARMSA is excited at the TM/sub 21/ mode to produce a conical pattern, which has a high gain in a low-elevation angle for mobile satellite communications. An effective design method using the equivalent circuit is indicated and, as a result, it is obvious that a broadband characteristic is obtained when each resonant frequency of the ARMSA and parasitic element is identical. Experimental results in the L-band showed satisfactory characteristics for vehicle antennas.

An analysis of antenna coupling between arrays on a polyhedron structure

Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Kellers GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations. >

Car-top annular-ring microstrip antenna

In Japan a car-top antenna for satellite communications is required to have high gain in the elevation angle range of 30 degrees -60 degrees . An annular-ring microstrip antenna (ARMSA) with a conical pattern which has high directivity in this angle range has been developed. The antenna gain is more than 3 dB in the elevation angle range of 30 degrees <or= theta <or=60 degrees .<<ETX>>

Radar Cross Section Analysis Considering Multi-Reflection inside a Radome Based on SBR Method

The authors propose the simple and efficient method based on the shooting and bouncing rays (SBR) method in order to evaluate multi-reflection effects inside a radome. In this paper, we show the analysis procedure of the proposed method. Next. we compare calculated data with some measured data in order to verify the proposed method. We confirmed that the proposed method is effective for the objects with radome except the areas where strong edge diffraction appears.

One-element diversity antenna with reactance-switching circuit for mobile phones

We have proposed a novel type of diversity antenna construction for compact mobile telephones. The proposed diversity antenna basically consists of one excitation element, the conducting-plate, and the reactance-switching circuit connecting between the end of the element and the conducting-plate, and need not install two excitation elements. We have demonstrated numerically and experimentally that the current phase distribution and radiation pattern can be controlled by appropriately switching the reactance value of the reactance-switching circuit. Our next works are to establish an optimum design theory and to investigate the performance in talking and browsing situations.