General TE/sub 011/-Mode Waveguide Bandpass Filters

A new structure for high-Q TE/sub 011/-mode circular waveguide cavities is introduced and shown to realize the most general bandpass-filter transfer functions. Methods of improving the mode purity and suppressing the degenerate TE/sub 111/ mode are presented. Several experimental narrow-bandpass filters having finite attenuation poles have been constructed; their measured responses show excellent agreement with theory. Average realizable unloaded Q's of 20000 and 16000 have been achieved at 8 and 12 GHz, respectively.