A new integrated optic technique for time delays in wideband phased arrays

Phased-arrays antennas are being employed in new generations of radar and communication systems that require the antenna to provide wide field-of-view (FOV), very narrow beamwidths, and wide instantaneous frequency bandwidths. Phased arrays designed to meet these requirements must have their aperture broken into subarrays with time delay units (TDUs) to minimize the dispersive effects of transmitting and receiving wideband waveforms through large arrays that use modulo 360 degree phase shifters to perform electronic beam scanning. The authors describe an integrated optic TDU. The TDU relies on a folded path optical waveguide to achieve time delays ranging from a few picoseconds to several nanoseconds. The folded path configuration utilizes thick phase gratings as reflective elements. These elements provide large angle deflection, high diffraction efficiency or reflectivity, wavelength multiplexing capabilities and form the basis for an electronically addressable switch. As a switching element they also offer high isolation due to their high diffraction efficiency