Tunable Waveguide-to-Microstrip Transition for Millimeter-Wave Applications

A novel waveguide-to-microstrip transition suitable for narrow as well as wide band applications at millimeter-wave frequencies is presented. It consists of a planar circuit having tapered sections of antipodal fin line and longitudinal slots whose length can be varied by tuning blocks placed underneath them. By selecting appropriate position of the tuning blocks, the transition can be optimized to achieve the desired bandwidth and center frequency. The tunability feature makes it very useful in test fixtures for device and circuit characterization.