Pattern and polarization reconfigurable loop antenna with circular high-impedance surface for 5G micro base station application

A novel type of loop antenna backed by four-element circular high-impedance surface (CHIS) for 5G micro base station application is presented. The CHIS is composed of four elements, each one in the shape of a truncated sector, and the complete CHIS acts as the reflection plane for the main radiating loop placed above. In all, the proposed antenna structure contains three variations, the size of which are all less than pi x 32(2) x 7 mm(3). By properly adjusting the distribution of excitations, the first antenna can steer its beam to all four quadrants with a tilted angle of theta = 15 degrees, and the remaining two antennas are capable of changing its polarization state among arbitrary linear polarization, left-handed circular polarization and right-handed circular polarization. Particularly, the second four-port antenna can also achieve pattern reconfiguration by steering its beam tilting towards four different quadrants, covering the space of -30 degrees <= theta <= 30 degrees with realized gain over 7.19 dBi. To validate the proposed concept, three antenna prototypes operating at 3.5 GHz are designed, fabricated and measured. The measured results agree well with the simulated ones, proving that the proposed antenna can achieve the desired reconfiguration.