An improved image impedance connected low loss SAW filter

We improved the reflecting electrode and the reflectivity weighting method of EWC/SPUDT. First, the width of reflecting electrode with the largest reflectivity is λ/8. Second, the reflectivity weighting is accomplished by changing width of the reflecting electrode from λ/8 to 3 λ/8. The filters utilizing the improved EWC/SPUDT result in lower loss or wider passband. Then, we developed an improved image impedance connected low loss SAW filter using EWC-SPUDTs with the λ/8 reflecting electrode as input and output IDTs. Filters using this improved structure result in more compact size and are fit for wideband. The experimental results of the DECT IF filter are given. The filter is fabricated in Y36° LiTaO₃ and housed a 11.4×5×2.2 mm³ SMD package. It has the center frequency of 110.59 MHz, an insertion loss lower than 4 dB, a 3-dB-bandwidth of about 1.4 MHz and a stop-band rejection better than 50 dB.