A new low loss SAW filter structure with extremely wide bandwidth for mobile communication systems

The authors present a low-loss surface-acoustic-wave (SAW) filter with a dual-track configuration which is characterized by a novel arrangement of interdigital transducers (IDTs) and reflectors in each acoustic track as well as a special electrical connection of the IDTs. Broadband filter characteristics can easily be achieved by using chirped components. The inherently good stopband rejection of the new structure has been further improved by applying proper weighting techniques to the IDTs and reflectors. A filter with a relative bandwidth of 10% and a center frequency of 200 MHz has been designed by means of a novel synthesis method. The filter has been fabricated on 128 degrees Y-X LiNbO/sub 3/. A minimum insertion loss of 4 dB, a small passband ripple of about 1 dB, and a stopband rejection of better than 35 dB were measured. Excellent agreement between simulation and measurement has been found.<>