Design of a 4×8 Substrate Integrated Waveguide Butler Matrix with Sidelobe Suppression at 60 GHz

This article presents a novel 4×8 SIW Butler matrix (BM) with sidelobe level (SLL) suppression. The BM operates at 60 GHz and is implemented with a new design to achieve a compact size, which would be attractive for future mm Wave wireless systems. This beamforming network uses straight SIW phase shifters with two apertures or two metal posts to pursue a smaller circuit area than with curved line phase shifters. Using a stepwise procedure and analyzing the design equations, the crossover and other components of the BM are also designed and optimized. The reflection and isolation coefficients are lower than -10 dB for all input ports and insertion loss magnitude imbalance is below 2.4 dB within the band from 57 GHz to 67 GHz. The slot array antenna fed by the BM shows an SLL lower than -21 dB for inputs 1 and 4 and lower than -14.5 dB for inputs 2 and 3 and provides ±45°beam switching.