Coaxial-to-circular waveguide transition with broadband mode-free operation

A simple transition between a circular waveguide and a coaxial cable having mode-free operation over more than an octave bandwidth is presented. The transition consists of a conical coaxial probe, a rectangular waveguide section and a linearly tapered transformer from the rectangular to circular waveguide. The transition shows a reflection coefficient of <; -20 dB, a transmission coefficient of >-0.57 dB and a higher-order mode level of <; -25 dB over a frequency range 1.04-2.53 times the TE₁₁ mode cutoff frequency.