Improved waveguide filters for applications involving circular polarization

Improved circular waveguide filters with responses having attenuation poles close to the passband are presented. Well-known circular iris filters, which are suited for circular polarization applications, are modified by replacing one or more irises by large circular waveguide sections. The inverter values. of such radial stubs are highly dependent on frequency and can generate attenuation poles in addition to the require passband inverter value. Two Ka-band examples demonstrate that attenuation poles can be created on both sides of the passband.