Octave bandwidth in‐line rectangular waveguide‐to‐coaxial transition using oversized mode conversion

Abstract

A very low‐loss in‐line rectangular waveguide‐to‐coaxial transition covering an octave bandwidth is presented. In order to obtain such frequency coverage, the transition employs oversized mode conversion, i.e. the rectangular waveguide dimensions are internally enlarged to modify the cavity cutoff frequency while obtaining good matching properties for a standard rectangular waveguide output port. A four‐step ridge transformer is included for the TE‐to‐TE 10 mode conversion in the whole frequency range. The transition, completed with a commercial SMA connector for the coaxial port, exhibits a return loss of around 25 dB with 0.1 dB insertion loss when measured in back‐to‐back configuration in the 10–20 GHz frequency range. From these results, an input matching around 30 dB and an insertion loss around 0.05 dB for a stand‐alone transition can be inferred.