Acousto-optic control of time delays for array beam steering

ABSTRACT This paper describes an acousto-optic signal processor that generates and controls the set of time delays required for RFantenna array true time delay beamsteering. The time delay controller can scan an RF array beam rapidly over a continuum ofangles with a tone whose frequency dete mines the pointing angle of the RF array beam. The time-delay controller alsoprovides the proper relative phases between the carriers of the time delayed signals at the RF of the antenna array. A proof-of-principle breadboard of the time delay controller was assembled. Results of the demonstration of the breadboard are presented. 1. INTRODUCTION Wide aperture, wide bandwidth phase steered array antennas suffer beam broadening when steered away from the array normal.Using time delays rather than phase delays between the array elements eliminates this beam dispersion. A brute forceapproach for implementing true time delay beamforming is to switch in different lengths of signal transmission delay linesbetween the common signal source and the antenna array elements; however, this approach can be bulky and cumbersome forscanning an array with a large number of elements over a wide range of nearly continuous angles.A number of investigators' have proposed using optical signal processing technologies for both phase and time delaybeamforming. This report describes a Rome Laboratory funded project conducted by Essex to demonstrate the proof-of-principle of an acousto-optic controller invented by Essex12 14 to generate and rapidly change the set of time delays of asignal for true time delay steering. The Essex approach is to use an acousto-optic Bragg cell as a delay line and to use a