New type double mode SAW resonator filters on 64/spl deg/ Y-X LiNbO/sub 3/

The double mode filters have the serious shortcoming that out-of-band rejection above the passband is quite poor. Hence a new structure of double mode SAW resonator filters is designed with the COM (Coupling Of Modes) theory with better out-of-band rejection characteristics while keeping all the beauties of the conventional double mode SAW filters. The second goal of the design is to reduce the planar size of the structure so that mass productivity of low frequency devices can be improved. Based on the conventional double mode filter structure, several IDT's and reflector gratings are added to or subtracted from it. As results of the investigation, several new double mode SAW resonator filter structures are developed. For the design, the effect of many design factors are investigated and the optimum values are determined. The new structure shows 10 dB more out-of-band rejection than the conventional type with 25% smaller device size. Good agreement is demonstrated between the analytical results and experimental results for an illustrative 325 MHz four pole resonator filter on 64/spl deg/ Y-X LiNbO/sub 3/.