an echo - compensating surface acoustic wave interdigital transducer in which the entire length of the end finger of the transducer at each end is connected directly or indirectly to at least one of the bus bars , the end finger extends only partially across the aperture of the transducer , and the space which is colinear with the end finger across the remaining portion of the aperture is not occupied by any surface - acoustic - wave - reflective structure . the end finger is substantially a quarter of an acoustic wavelength out of phase with the nearest interior finger with respect to an incident wave at the operating frequency of the transducer , so that the acoustic reflections of the end finger and the nearest interior finger are in phase - opposition to each other . in addition , the end finger spans one half of the transducer aperture , and is arranged to permit unobstructed acoustic reflection from the nearest interior finger over the other half of the aperture at one of the ends of the transducer , so that the resulting phase - opposed reflections are equal in amplitude in order to achieve mutual cancellation .