Switched and Steered Beam End-Fire Antenna Array Fed by Wideband Via-Less Butler Matrix and Tunable Phase Shifters Based on Liquid Crystal Technology

This article presents the design of a Ka-band beam-switchable and beam-steerable endfire planar Yagi-Uda antenna array fed by a wideband Butler matrix, combining continuously tunable phase shifters based on a liquid crystal (LC) technology. The proposed array consists of four wideband 3 dB 90 degrees branchline couplers, two novel wideband via-less crossovers, LC-based 135 degrees microstrip (MS) delay line phase shifters, and planar endfire Yagi-Uda antennas. The Butler matrix realizes beam switching, while LC phase shifters enable continuous beam steering inbetween the discrete beam positions. In this way, long delay line phase shifters are avoided for achieving 360 degrees, reducing the phase shifter insertion losses (IL). Besides, such a hybrid beam steering method is expected to respond faster and more accurate. The array has two metallized layers, which can be easily fabricated by standard photolithography procedures. The fabricated array demonstrator is measured in terms of S-parameters and far-field patterns. The measured return loss and isolation of the array are both >= 15 dB from 26 to 30 GHz. The beam is switchable among +/- 15 degrees and +/- 45 degrees in E-plane. By applying bias voltage up to 5 V to the LC phase shifters, the beam can be further continuously steered, covering almost -60 degrees to +60 degrees with acceptable sidelobe level. The maximum gain of the array is estimated to be 5.6 dBi. The radiation efficiency is 12%.