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 TM
₂₀
, TM
₃₀
, TM
₄₀
, and TM
₅₀
is decreased and combined with the dominant mode (TM
₁₀
) one. These live 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 0.5λ
₀
× 0.5λ
₀
and the height is only 0.1λ
₀
(λ
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 S11 <; -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.