Surface ultrasonic wave delay lines with dispersive time-frequency characteristics have been made using interdigital electrode arrays with variable element spacings on LiNbO3. The devices operate at 60 MHz with low insertion loss and a 3-dB bandwidth over 25 percent. A model has been devised which accurately predicts the phase and amplitude characteristics of the devices. Weighting” the array to improve the phase characteristic is described. Copyright © 1969 by The Inshtute of Electrical and Electronics Engineers Inc.