Asymmetrically truncated SAW transducers

A symmetrically designed finite impulse response (FIR) SAW transducer has linear phase characteristics and symmetry in the bandpass response. An analysis is presented which shows that a linear phase SAW bandpass filter retains symmetry about center frequency in its magnitude, phase, and group delay characteristics when asymmetrically truncated about the center of the transducer spatial array. While passband amplitude ripple characteristics can often be improved, a trade-off occurs in group delay and phase behavior. The degradation in group delay and linear phase is not severe, however, and the technique may be applied to conserve overall substrate dimension parallel to the propagation direction, consistent with design constraints on the filter performance. Furthermore, both the input and output transducers may be modified in a complementary fashion so that overall linearity in group delay and phase is retained. Experimental confirmation is presented.