A Multi-linear Polarization Reconfigurable Unidirectional Patch Antenna

A novel multi-linear polarization (multi-LP) reconfigurable unidirectional circular patch antenna is proposed, which can switch among four LPs at every 45 degrees rotation. The patch antenna is fed in the center and shorting posts are used to excite TM11 mode with LP. By controlling the connections between the four shorting posts and the ground plane using p-i-n diodes, four reconfigurable polarization states at phi = 0 degrees, phi = 45 degrees, phi = 90 degrees, or phi = 135 degrees can be realized. The size of this antenna is about 0.57 lambda x 0.57 lambda x 0.07 lambda at 2.45 GHz. It can be easily fabricated and has a simple biasing network. The measured overlapping impedance bandwidth for different polarizations under the condition |S11| <= -10 dB is from 2.33 to 2.50 GHz, which agrees well with the simulated one. Moreover, the antenna maintains stable radiation patterns and the measured realized gains range from 5.3 to 5.9 dBi.