Modeling a longitudinally coupled dual-mode leaky-SAW resonator filter with enhanced upper-sideband suppression

Recently, it has been experimentally reported that enhanced upper-sideband suppression of a longitudinally coupled (first/third) dual-mode leaky SAW ( LSAW) resonator filter may be obtained by incorporation of a selectively va lued capacitor between input and output terminals. In this paper, coupling- of-modes (COM) and bandstop-filter modeling is applied to realize this enha nced suppression. Tradeoffs are examined between upper and lower sideband s uppression levels caused by the ensuing capacitive coupling between input a nd output terminals. Good agreement is obtained between this theory and rep orted experimental results for an 800-MHz band cellular filter.