New wavelength division multiplexing true-time-delay network for wideband phased array antennas

Abstract. Phased array antennas (PAAs) offer many advantages including steering without physical movement, accurate beam pointing, increased scan flexibility in two dimensions, precise PAA element phase and amplitude 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. We describe a new lower complexity and cost photonic TTD system which we call WDM delay broadcasting TTD. This approach (1) encodes fixed delays with wavelength, (2) makes available all of the delays at each of the subarrays, and (3) selects the appropriate delay using an optical filter (with correction via the element electronic delay line). The results of this effort show that it is indeed possible to design and construct a photonically controlled TTD network that will exhibit the performance and cost benefits needed for widespread deployment in government and commercial phased array radar antenna systems.