A Millimeter-Wave Broadband Transition of Air-Filled Rectangular Waveguide to Differential Substrate Integrated Waveguide

A right-angle broadband transition between air-filled rectangular waveguide (RWG) and the differential substrate integrated waveguide (SIW) is proposed at Ka-band. By utilizing two SIW cavities with two H-shaped slots in the proposed transition, a simulated impedance bandwidth wider than 45.9% ranging from 25.5 to 40.7 GHz for return loss less than -15 dB can be achieved. The insertion loss of a single transition is less than 0.1 dB within the operating band. Meanwhile, the phase difference and amplitude imbalance between the two differential output ports are less than 180 degrees +/- 0.15 degrees and 0.02 dB, respectively.