A Design of Compact Ultrawideband Circularly Polarized Microstrip Patch Antenna

As it is well known, microstrip patch antennas are commonly used, because they are compact and it is easy to achieve a unidirectional radiation pattern with circular polarization. However, the bandwidth of patch antennas is quite narrow, which limits their use in ultrawideband (UWB) applications. In this communication, a wideband enhancement method based on a multimode analysis of patch antennas is proposed. By adding suitable shorting loads on the patch, the resonance frequency of the higher order modes TM20, TM30, TM40, and TM50 is decreased and combined with the dominant mode (TM10) one. These five modes provide a wide operating band. Using this bandwidth enhancement method, a compact UWB patch antenna with unidirectional radiation pattern and circular polarization is designed. The size of the patch is only 0.5 lambda(0) x 0.5 lambda(0) height is only 0.1(lambda) (lambda(0) is the free space wavelength at the center frequency). The simulation and measured results show that the proposed antenna has a bandwidth of 85% for S-11 < -10 dB and realized RHCP gain >6 dBic from 2.2 to 5.5 GHz. The proposed design method is suitable for UWB CP patch antenna applications.