Quasi-optical bandpass and bandstop notch filters have been designed employing the synthesis techniques that are generally employed in waveguide filter design. The performance of a bandstop filter consisting of a number of coupled Fabry-Perot resonators will be reported.
A. R. Harvey, A. R. Harvey,
"A 140 GHz quasi-optical notch filter", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15764Z (1 October 1991); doi: 10.1117/12.2297892; https://doi.org/10.1117/12.2297892