Suppression of Bulk Wave Scattering on Non-synchronous Area in SAW Devices

The losses due to bulk wave scattering on non-synchronous area in SAW device was studied using boundary element method combined finite element method(FEM/BEM).We used a typical one-port hiccup resonator as reference structure.Using gap with gradually changing parameters to replace the central free gap in hiccup resonator,we found that it is possible to significantly increase its Q-factor while keeping the resonant frequency unchanged.Two kinds of structures were studied and compared,one is "distributed" gap,another one is the so-called "accordion" gap.It is found that distributed gap is better than accordion gap.We replaced the metallized gaps in the traditional DMS filter with distributed gaps.By numerical simulation we can find an optimal combination of pitch and metallized ratio of the gaps,reducing the insertion loss by about 0.3 dB.