Characterization of a 4 × 4 substrate integrated waveguide Butler matrix at 60 GHz for two‐dimensional beam steering

Abstract

A 4x4 substrate integrated waveguide (SIW) Butler matrix for two-dimensional (2-D) beam steering operating at 60 GHz is developed and experimentally evaluated in this article. The SIW beamforming network is a Butler matrix that is implemented with new designs of its constituent components in order to achieve a compact design. Namely, an SIW phase shifter that uses periodic rectangular slots is introduced for the first time at 60 GHz to replace the more area-consuming meandered SIW. The phase shifter prototype, fabricated and measured as a proof of concept, demonstrates achieving an additional 20.3° of phase shift with using only 3 apertures without increasing the length or meandering the SIW line. The hybrid coupler and crossover sections of the SIW Butler matrix are also optimized to reduce the overall area of Butler matrix by 53.9%. The SIW Butler matrix prototype is fabricated and measured demonstrating achieving the differential output phase values needed to switch the beam of a 2-D array in four quadrants while keeping the insertion loss magnitude imbalance of below 1.47 dB from simulations and 3.34 dB from measurements.