A surface acoustic wave resonator has a transducer (12) and grating reflectors (18, 20) mounted on a piezoelectric substrate (10). The transducer comprises a number of interdigitated transducers (14, 16) which are series connected and aligned with one another. The grating reflectors (18, 20) are located on opposite sides of the composite transducer (12) and have aperture lengths extending at least over the width of the paths of the surface acoustic waves from the transducer.