Low-Profile Wideband High-Gain Reconfigurable Antenna With Quad-Polarization Diversity

A low-profile, wideband, high-gain reconfigurable antenna, which is capable of switching among four linear polarizations (LPs) at every 45° rotation, namely, 0°, 45°, 90°, and 135° LP, is presented. The proposed structure is based on two half-ellipse-shaped dipoles arranged perpendicularly and is center fed by coaxial cable. The antenna polarization can be switched by selecting the appropriate dipole arms to be excited as well as controlling their phases using p-i-n diodes. To achieve low-profile, high-gain, and unidirectional radiation patterns in a wide range of frequency, a combination of an artificial magnetic conductor and a shallow pyramid-shaped cavity is also utilized in this design. An optimized prototype with low profile of $0.1\lambda $ at the lowest operating frequency yields a measured overlapped impedance bandwidth (BW) of 53.9% for all polarization states. In addition, a radiation efficiency of greater than 78% and measured broadside gain from 6.8 to 10.9 dBi are observed over the entire operation BW.