Design of a circular waveguide-to-microstrip coupling probe for a submillimeter-wave application

A design that uses a microstrip probe inserted into a circular waveguide and tuned with a noncontacting adjustable short circuit is described. Although the use of a circular (instead of rectangular,) waveguide is restrictive in bandwidth, the coupling probe designed for submillimeter-wave operation should yield a 10% bandwidth with >or=20 dB return loss. The use of a noncontacting short circuit allows the probe to be tuned without the need for electrical contact with the waveguide walls.<>