Shoulder Suppressing Technique for dual mode SAW resonators

A new type of RF filter which combines the excellent far out rejection of an LCR Filter with the sharp transition band of a Ladder Filter is introduced. The new structure, called SST for Shoulder Suppressing Technique, consists of a dual mode resonant cavity where the input and output of the resonator are electrically coupled via a small interdigital capacitor. Properly designed, electrical notches can be placed on both the low and high side of the pass band, sharpening the transition band and completely eliminating the hump on the high side of the pass band which is a characteristic of traditional LCR filters. We successfully designed SST-LCR filters with no characteristic high side hump. Designs for the cellular and K-PCS bands have been developed which have superior shape factors, 50 dB out of band rejections and insertion losses of 2.5 and 3.5 dB respectively.