Broadband coaxial line to rectangular waveguide transition for a microwave tomography sensor

A broadband coaxial line to rectangular waveguide transition for a microwave tomography sensor is presented. It consists of two parts: a coaxial line to double ridged waveguide transition and a double ridged to rectangular waveguide transformer. The transition is well matched (reflection coefficient below -10 dB) and has a low insertion loss (below 3 dB) in a wide frequency range from approximately 0.85 GHz to 4.4 GHz. Due to the symmetric design of the double ridged waveguide, a large single mode propagation bandwidth (0.6 GHz to 3.2 GHz) and a good higher order mode suppression (greater than 10 dB above 3.2 GHz) is achieved. The transition design is described in detail, analyzed by 3D electromagnetic field simulations, and validated by measurements.