A waveguide branch-line crossover based on metal gratings

A waveguide branch-line crossover with broad bandwidth is designed for beam-forming networks in millimeter wavebands. To realize the power coupling between two parallel branch lines, a substrate with metal gratings patched replaces the common E-plane waveguide wall. Compared with the traditional crossover with coupling vias, the metal gratings achieve continuous and efficient power coupling, endowing the proposed crossover with advantages in compactness and broad bandwidth. A simulation-assisted transfer-matrix approach is used to rapidly estimate and optimize the parameters of the crossover. The coupling obtained from the simulation is over -0.5 dB from 32.1 to 39.1 GHz, with isolation greater than 15 dB and reflection less than -20 dB. A prototype is fabricated, and the measurement results agree with the simulation results, demonstrating that the proposed crossover is a promising candidate for millimeter-wave beamforming networks.