Via-hole-less planar microstrip-to-waveguide transition in millimeter-wave band

A via-hole-less planar microstrip-to-waveguide transition is proposed. A proximity coupling type transition requires via holes to prevent a leakage of parallel plate mode in the substrate. We propose to replace the via holes to the choke structure. In order to remove the via holes of the proximity coupling type transition, a choke of the parallel plate waveguide was applied. The dimensions of the waveguide short metal with a parallel plate waveguide which is located on the waveguide end is examined to achieve the choke circuit. The length from the edge of the waveguide short metal to the edge of the waveguide aperture is set to a quarter wavelength of the parallel plate waveguide which is constructed with the closely-spaced waveguide short metal and the surrounding ground of the patch element. All the dimensions were optimized numerically. Proposed transition has an insertion loss of 0.68 dB from 76 to 77 GHz, and a bandwidth of 6.4 % (4.9 GHz) for the reflection coefficient below -15 dB.