Single-feeding Circularly Polarized Tm21- Mode Annular-ring Microstrip Antenna for Mobile Satellite Communication

A novel TM21-mode circularly polarized (CP) annularring 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 1.601 GHz. The proposed antenna can be used in mobile earth-station equipment for satellite positioning and communication systems in global or local.