A Liquid-Metal-Enabled Reconfigurable Feed Network for Multipolarization Arrays

This article presents a novel reconfigurable feed network that allows the switch of antenna arrays across four different polarization states. Different from most previous multipolarization antennas, the reconfiguration is implemented solely in the feed network without disturbing the radiation element. The key enabler is a reconfigurable coupler that switches between two circuit functions—a branch-line coupler or a crossover—through altering the line widths of its parallel branches. This is only made possible by using liquid metals (LMs). A double-pole-double-throw (DPDT) switch, also enabled by LM, is employed to select the input port of the reconfigurable coupler. The switch and the reconfigurable coupler form the reconfigurable feed network, providing four states of excitation to the antenna. The reconfigurable coupler, the switch, and a 2 $\times$ 2 array have been designed and experimentally verified with the LM actuation. As a branch-line coupler, the reconfigurable coupler shows excellent amplitude and phase balance within 0.04 dB ( $\vert\vert S_{{21}}\vert$ – $\vert S_{{31}}\vert\vert$ $<$ 0.04 dB) and 90 $^{\circ}$ at 3.5 GHz, whereas, as the crossover, it has an isolation over 25 dB. The switch exhibits an isolation of 50 dB. The measured peak gain of the array is 14.7 dBic. At 3.5 GHz, the measured axial ratio (AR) associated with the right-hand circular polarization (CP) state is 1.0 dB. The speed of switching and power handling associated with the LM have been discussed. The use of the LM has enabled a unique way of circuit reconfiguration and a full polarization-reconfigurable multifunctional antenna.