A two-step synthesis of broadband ridged waveguide bandpass filters with improved performances

A quarter-wave broadband ridged waveguide bandpass filter with improved attenuation has been designed and realized. The two-step synthesis uses an equivalent network whose parameters are obtained with a multimodal variation approach that characterizes the discontinuities involved in the structure. It is shown that the frequency behavior of the filter is determined at this step by the chosen filter prototype. The structure is optimized taking into account all side effects (higher order modes, dispersion) and the rectangular to ridged waveguide transformer. Predicted data are compared with measured data and good agreement is observed. It is shown how the use of λ/4 resonators improves the attenuation in the upper stop-band and reduces the filter volume, which is important in on-board satellite telecommunication systems