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

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3 Author(s)
H. Ohmine ; Antenna & Microwave Group, Mitsubishi Electr. Corp., Kamakura, Japan ; Y. Sunahara ; M. Matsunaga

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 Ω. 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 TM21 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

Published in:

IEEE Transactions on Antennas and Propagation  (Volume:45 ,  Issue: 6 )