Minimum Insertion Loss Microwave Filters

Equal-element band-pass filters provide the lowest midband insertion loss possible with a given number of resonators and a specified rejection bandwidth or skirt response. Losses can often be reduced by 1 to 2 db. A technique applicable to narrow-band equal-element filters has been developed that holds for both large and small dissipation factors. Using this technique, circuit constants can be determined for filters having from two to eight coupled resonators. Formulas are given for lumped-constant and strip-transmission-line circuits.