Photonically Controlled True-Time-Delay Wideband Radar

The next generation Navy radar systems will require shared active phased array antennas (PAA). PAAs offer many advantages including steering without physical movement, accurate beam pointing, increased scan exiility in two dimensions, precise PAA element phase and amp etude control to obtain low sidelobes, and reduced power consumption and weight. The complexity associated with controlling the many thousand array elements, while handling the broad bandwidth required of a shared antenna, makes the marriage of photonics and microwave radar attractive. To satisfy the simultaneous requirements of wide bandwidth and large antenna scan angle, true-time-delay (TTD) steering techniques are required so that efficient elemental vector summation (in the receive mode) or distribution (in the transmit mode) can be obtained that is independent of frequency or angle. our approach utilizes the inherent advantages of optical fiber for both signal distribution and TTD beam steering using a combination of laser diodes, integrated optical modulators, and integrated and bulk optical switches. All of these components are commercially available with their continued development driven by the massive commercial market for digital fiber optic communication and cable television. our design avoids active optical devices which severely limit system dynamic range and noise figure.