Dual-Band Omnidirectional Scanning Array Using Liquid Metal-Enabled Reflection-Type Phase Shifters

This article demonstrates a dual-band omnidirectional beam-scanning antenna array. A key innovation is a dual-band reflection-type phase shifter using liquid metal (LM)-enabled shunt switches. A stub-loaded branch-line coupler allows the dual-band operation. The switch is based on the via-pad-slot (VPS) structures, unlike conventional switches, without requiring any bias lines. They are used to alter the path length of the reflected signal from the shorted termination. The use of the LM ensures high isolation switches and phase shifters with a wide phase range. The scanning array also features a wideband 1-to-8 Wilkinson power divider and a $1\times 8$ dual-band dipole array. The array has the same beam direction in both frequency bands when the phase increment is adjusted. To verify the proposed method, a microstrip VPS switch, a dual-band reflection-type phase shifter, and the whole array have been fabricated and measured. A wide phase range of 360°/720° at 1.75/3.5 GHz has been achieved, while the average insertion losses are 1.4 dB at 1.75 GHz and 2 dB at 3.5 GHz, respectively. The dipole array shows omnidirectional dual-beam scanning along the E-plane at both bands, yielding realized gains of 7.2 and 9.74 dBi, respectively. The dual-band design method and the LM-based implementation techniques can be applied to other wide-coverage scanning arrays and high-performance phase shifters.