Doubly apodized SAW filters

The design of a surface acoustic wave filter having two apodized in-line transducers is presented. The positions and weights of the taps in both transducers are obtained simultaneously by considering the finger-by-finger interaction between the two transducers. Two design optimization criteria are compared. A device consisting of two 21-tap transducers with a 10 MHz passband centred at 50 MHz is built on 128° rotated Y-cut LiNbO3 to verify the design. We show that the sidelobe suppression is limited by diffraction, which was not included in the design procedure. The response is compared to that obtained by a singly-apodized SAW filter of comparable length designed with the Remez exchange algorithm.