Optical BEAMTAP beam-forming and jammer-nulling system for broadband phased-array antennas

We present an approach to receive-mode broadband beam forming and jammer nu lling for large adaptive antenna arrays as well as its efficient and compac t optical implementation. This broadband efficient adaptive method for true -time-delay array processing (BEAMTAP) algorithm decreases the number of ta pped delay Lines required for processing an N-element phased-array antenna from N to only 2, producing an enormous savings in delay-line hardware (esp ecially for large broadband arrays) while still providing the full NM degre es of freedom of a conventional N-element time-delay-and-sum beam former th at requires N tapped delay lines with M taps each. This allows the system t o adapt fully and optimally to an arbitrarily complex spatiotemporal signal environment that can contain broadband signals of interest, as well as int erference sources and narrow-band and broadband jammers-all of which can ar rive from arbitrary angles onto an arbitrarily shaped array-thus enabling a variety of applications in radar, sonar, and communication. This algorithm is an excellent match with the capabilities of radio frequency (rf) photon ic systems, as it uses a coherent optically modulated fiber-optic feed netw ork, gratings in a photorefractive crystal as adaptive weights, a traveling -wave detector for generating time delay, and an acousto-optic device to co ntrol weight adaptation. Because the number of available adaptive coefficie nts in a photorefractive crystal is as large as 10(9), these photonic syste ms can adaptively control arbitrarily large one- or two-dimensional antenna arrays that are well beyond the capabilities of conventional rf and real-t ime digital signal processing techniques or alternative photonic techniques . (C) 2000 Optical Society of America OCIS codes: 070.1060, 190.5330.