A Full Ka-Band Compact Coax-to-Waveguide Transition With Shaped Internal Profile and Enhanced Fabrication Process Flexibility

This paper reports on the design and implementation of a size-compact and wideband E-plane coax-to-waveguide transition featuring geometrically shaped internal profile of the waveguide cavity. The shaping involves properly attaching a parasitic cavity to the rectangular waveguide, filleting the cavity edges, and constructing a smooth connection from the parasitic cavity to the waveguide. The transition devised out of the shaping is able to perform wideband and low-loss transmission free of using any tapered waveguide mode transformer as conventional. More significantly, the shaping results in smooth cavity profile that is highly compatible to either subtractive or additive manufacturing technology. This upgrade in the structure enhances flexibility in the fabrication process of the transition. Adapter prototypes based on the transition are engineered and demonstrate in the entire Ka band return and insertion losses of >18 dB and <0.5 dB, respectively, showing great potential for applications in microwave network measurement.