A Wideband 16x16 Butler Matrix for Millimeter-Wave Beam-Switching Applications

This paper presents a compact and wideband 16×16 Butler Matrix (BM) beam-switching network operating over the frequency band from 37 GHz to 42 GHz. The structure is designed based on a three-layer stack-up and consists of wideband aperture couplers and Schiffman phase shifters. PCB VIA interconnect is adopted to avoid crossover and therefore minimizing the circuitry footprint and design complexity. The simulation results show a return loss and isolation better than -9 dB and -12 dB, respectively with an average insertion loss of 6 dB over the bandwidth. The BM network has a compact size of 60 mm × 26 mm which makes it a suitable beam-switching network option for integration inside millimetre-wave consumer electronics applications. The designed 16×16 BM has been fabricated and measured. Array factor is plotted using the simulated and measured phases and magnitudes of the network. The array factor plots show that by feeding the input ports separately, 16 directional beams are produced covering ±68° spatial angle at the center frequency of 39.5 GHz.