A novel TM21-mode circularly polarised (CP) annular-ring microstrip antenna (ARMSA) is presented. The annular ring is designed working at TM21 mode, and conical radiation pattern is obtained. At the inner of annular ring, a simple ring-shaped feeding line is arranged to implement impedance matching and CP operation. Therefore, the antenna has good impedance and CP performance, as well as a compact structure. The measured results indicate that the antenna has high low-elevation gains and omnidirectional azimuth coverage. The peak gain reaches 4.3 dBic at elevation angle of 47°, and in the range of 10°-70°, the gain is above 0 dBic. The impedance bandwidth for S11≤-10 dB is 2.3% at 1.601GHz. The proposed antenna can be used in mobile earth-station equipment for satellite positioning and communication systems in global or local.
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