IIDT type SAW filter using acoustic reflection cancel condition with solid IDT

The performance of an IIDT (interdigitated interdigital transducer) filter using the acoustic-reflection cancel condition of the solid IDT is investigated for the substrate A1/128° Y-X LiNbO₃ . The acoustic reflection cancel condition is a combination of 2 d/λ=0.5 and h/λ=0.026 in the solid fingers. Near this condition the solid finger width d and thickness h dependence of the acoustic reflection coefficient is calculated by the finite-element method. The solid-finger width needs to be carefully controlled during the etching process, to avoid filter response distortion caused by the acoustic reflection of the IDT and phase velocity difference between the IDT and the propagation area. A new IIDT-type SAW (surface acoustic wave) filter configuration with a reduced number of fingers is proposed. This filter has a low shape factor (the 1 dB-bandwidth to 6-dB bandwidth ratio is 1.1) and a small ripple pass band