Microwave Band-Stop Filters with Narrow Stop Bands

Band-stop filters can be used to eliminate a band of frequencies, or to separate such a band from other frequencies; if properly designed, the insertion loss at frequencies outside the stop-band can be minimized. The filters considered here have stop-band bandwidths up to a few per cent, and equiripple or maximally flat characteristics in the passband. Design formulas are presented. The effect of dissipation loss is included. A strip-line filter and a waveguide filter were constructed. Experimental results conform closely to the performance predicted by theory.