Mode conversion filters

Resonance of higher order modes in waveguides can be advantageously used to make band rejection filters of unusual simplicity and low loss. The region where the resonance takes place can be obtained either by a change of cross section of the waveguide or by the inclusion of dielectrics. The relative advantages and experimental results obtained at 11 and 55 kmc are discussed. Finally it is shown how to use the resonance of converted modes to design channel dropping filters.