Design and performance of 1 GHz range image impedance connected low loss SAW filters

Abstract

An improved design technique of image impedance connected low-loss filters is presented. The technique makes it possible to control the fractional bandwidth in the range 0.7-3% on 36 degrees -rotated Y-cut LiTaO/sub 3/ (36-LTO). An accurate and simple method is used for characterization of propagation on 36-LTO above 1 GHz. The mass-loading coefficient was derived from experimental data and the attenuation coefficient was found to be 10/sup -2/ dB/ lambda /GHz, which is a much higher value than for LiNbO/sub 3/ but still compatible with low-loss filter manufacturing. Four high-performance low-loss SAW (surface acoustic wave) filters were manufactured on 36-LTO with various fractional bandwidths from 0.65 to 3%. Insertion losses as low as 6.5 dB at 800 MHz and 8.5 dB at 1400 MHz were obtained and out-of-band rejections as high as 50 dB were achieved, even with devices mounted in chip carriers. >