A Low-Cost Wideband 77-GHz Planar Butler Matrix in SIW Technology

This communication presents a low-cost 77-GHz switched-beam slot antenna array driven by a Butler matrix. In the proposed configuration, four broadband couplers are combined and crossovers are effectively avoided. In this case, the overall circuit and beamforming network losses are considerably reduced. A 4 × 4 planar SIW Butler matrix is designed and demonstrated for integrated beamforming network applications, which exhibits about 7 degrees phase error and ±0.75 dB coupling imbalance over 11% bandwidth. This experimentally prototyped matrix is integrated with a four-array slot antenna on the same substrate. An alternating displacement of the slots in subsequent radiating waveguides is proposed to save the arrangement of the input ports and to achieve broadband performances. Measured radiation patterns are in good agreement with simulated counterparts over the proposed 77-GHz frequency range.