A true time delay system and method for an optical carrier signal modulated with a microwave signal. The system includes a beam deflector, with the optical signal being imaged onto the beam deflector, a stationary reflective diffractive grating arranged in a Littrow configuration, a focusing element arranged between the beam deflector and the stationary reflective diffractive grating. In operation, the beam deflector steers the optical beam across the clear aperture of the focusing element and the focusing element transmits the steered beam to the reflective diffractive grating. A change in optical path length experienced by the optical beam as the beam is scanned across the grating surface results in a relative phase delay in the optical beam. The beam deflector can be a rotating mirror, an acousto-optic beam deflector, or an electro-optic beam deflector. The focusing element can be a lens or a curved mirror.