Harmonic absorbing filters in waveguide

Describes the techniques used to absorb unwanted modulation products and harmonics in waveguides. A good match to unwanted frequencies has been obtained by inserting a screw (band stop filter) into the waveguide and absorbing the reflected wave in waveguide terminations mounted over transverse slots positioned a half-wavelength (of the additive frequency combination) either side of the screw. Additional screws in the terminating and main waveguides permit fine adjustment for matching the waveguide at the terminal which connects to the mixer. For higher order modulation products or frequencies a similar technique can be applied to a ridged waveguide. The coupling from rectangular to ridged waveguide was effected by a probe soldered to the centre of the ridge and fine adjustment of the compsite filter was obtained by miscellaneous screws. The main advantage claimed is to guarantee a given suppression even between large mismatches in an overmoded waveguide.