Susceptance-loaded evanescent-mode waveguide filters

The paper extends the theory of evanescent-mode filters to include susceptance loading midway between cavities. It is shown that inductive loading may be employed to provide a substantial reduction in the length of narrowband filters without significantly increasing the insertion loss. By replacing conventional capacitive-tuning screws with quartz-rod tuning elements, losses comparable with conventional waveguide filters are obtained in filters requiring about half the volume.