A Compact Reconfigurable Feeding Network for 5G Quadri-Polarization Antennas

This letter presents a compact reconfigurable feeding network, which can provide four polarizations. The feeding network includes a branch-line hybrid, two p-i-n diodes, and two grounded capacitors. By manipulating the on/off states of the two diodes, the capacitor can be selectively integrated into the hybrid circuit. Hence, the power distribution of the output ports is changed. The feeding network operating in state I provides a pair of orthogonal linear polarizations (LPs) when both diodes are turned off. The feeding network operating in state 11 provides a pair of orthogonal circular polarizations (CPs) when both diodes are turned on. Experimental results show that the proposed feeding network has a wide operating bandwidth from 3400 to 3800 MHz with S-11 <= -20 dB and isolation level > 20 dB in two states. Moreover, the amplitude imbalance of the output ports is less than 1.3 dB with a 90 degrees stable phase difference when the feeding network operates in state 11. The presented reconfigurable feeding network is suitable for fifth-generation (5G) quadri-polarization antennas.