Design of impedance transforming 90 degree patch hybrid couplers

A miniaturized 3-dB patch hybrid coupler with arbitrary impedance transforming ratio is presented. By loading a pair of asymmetric cross slots on a squared patch resonator, the overall size of the hybrid is reduced and the required 3-dB conditions can also be achieved with different transformed output-port impedances. Based on the equivalent transmission line model, we provide a heuristic design guide and physical understanding for this kind of patch-based 90 hybrid couplers. Finally, a prototype of the coupler with 1.3 transforming ratio is designed implemented at 4.2 GHz. The measured results show a good agreement with those obtained from the simulation.