The Design of Microstrip Patch Antenna with Four Polarizations

An antenna that is capable of exciting four different kinds of linearly polarized waves across an overlapped frequency band by four independent feeding ports is presented. The four polarizations embrace the x- and y-polarized waves which have broadside patterns and the θ- and φ-polarized waves which have conical patterns. The x- and y-polarizations (TM₁₁ mode) and the θ-polarization (TM₀₂ mode) are achieved by exciting a circular patch with four shorting posts and five L-shaped probe feeds, while the φ-polarization is achieved by exciting four slots cut on the patch to produce radial magnetic currents. The performance of the antenna is studied numerically and experimentally. A prototype antenna is built and it achieves four polarizations overlapped at about 2.1 GHz, a gain of about 4 dBi for the two conical waves, and a gain of about 11 dBi for the two broadside waves.