Loss reduction of microstrip-to-waveguide transition suppressing leakage from gap between substrate and waveguide by choke structure

A microstrip-to-waveguide transition can be used for connecting antennas and backed RF circuits. Loss of the transition due to the leakage from the gap between the substrate and the waveguide has been a serious problem in the millimeter-wave band. A choke structure is provided in the gap at the quarter wavelength away from the waveguide edge to suppress the leakage. The effect to use the choke structure is demonstrated by simulation in this paper.