Polarization-Reconfigurable Antenna Array for Millimeter-Wave 5G

The design of 5G 4-element antenna array system with the capability of switching its operation between right hand circular polarization (RHCP) and left hand circular polarization (LHCP) is proposed. The CP-reconfigurability is achieved by electronically switching two PIN-diode pairs in the feeding circuit, which consists of a branch line coupler and two feeding arms. The proposed configuration reduces the number of tuning elements and allows the use of imperfect PIN diodes at millimeter-wave frequency. The fabricated prototype exhibits a 3-dB axial ratio bandwidth from 27.2 to 28.35 GHz. A maximum measured gain of about 6 dBic and a radiation efficiency of around 51% over the bandwidth are achieved for both CP states.