Simple Elliptic-Function Filters Made of Rectangular Waveguide and Semi-Rigid Cables

A semi-rigid cable makes a conventional waveguide filter into an elliptic-function filter. A four-resonator elliptic-function filter having a simple construction and a selectivity equivalent to that of a ten-resonator Butterworth filter has been developed by adding a semi-rigid cable to a conventional rectangular waveguide bandpass filter. Although using semi-rigid cable, this filter is equivalent to a rectangular waveguide bandpass filter in unloaded Q. In this filter, two signal portions having passed through different routes offset each other at attenuation poles. Also, a six-resonator filter has been constructed with two semi-rigid cables.