Design of Millimeter-wave Rectangular Waveguide to HMSIW Transition Based on Trapezoidal-shaped Probe

In this letter, a compact rectangular waveguide-to-half mode substrate integrated waveguide (HMSIW) transition is presented. It uses a trapezoidal-shaped probe to couple the energy from rectangular waveguide to HMSIW. A back-to-back test module at Ka-band is fabricated and measured. It provides a return loss better than 15 dB and an insertion loss of 0.85 to 1.3 dB within a frequency range from 25 to 40 GHz. The circuit size of the proposed transition is reduced by approximately 81.8% as compared with the waveguide-to-HMSIW transition using antipodal fin-line. Additionally, no intermediate transition is needed for this transition, which simplify the design of transition circuit. The measurement results agree well with simulation results, which validate the feasibility of the transition. Also, a tolerance analysis is performed via the simulation to verify the reliability of this transition design.