Distributed Coherent Aperture Measurements for Next Generation BMD Radar

This paper describes the distributed coherent aperture work being carried out at MIT Lincoln Laboratory in support of the next generation radar (NGR) program under the direction of the Radar Systems Technology (RST) group within the Missile Defense Agency/Advanced Systems (MDA/AS) Directorate. The NGR concept achieves transportability and high-radar sensitivity by coherently combining multiple distributed radar apertures in a building block manner. The operational concept uses orthogonal noise-like waveforms and multiple-input multiple-output (MIMO) techniques for cohere-on-receive operation and for adaptively estimating the transmit coherence parameters. In cohere-on-transmit mode, like waveforms are used and the relative phase and transmit time of each transmit pulse is adaptively adjusted so that the transmitted pulses arrive at the target in-phase and at the same time. In cohere-on-receive mode, an N² signal-to-noise ratio (SNR) gain is achieved over a single aperture when the orthogonal waveforms are combined coherently. In cohere-on-transmit mode, full coherence is achieved on both transmit and receive for an N² SNR gain over a single radar. The NGR concept and recent highly-successful distributed aperture measurement campaigns are described. These measurements were carried out at the white sands missile range (WSMR) using the Lincoln Laboratory Wideband MIMO Distributed Aperture Test System in July 2005 and at the Air Force Research Laboratory (AFRL) Ipswich Antenna Range Facility in August 2004. Wideband coherence on transmit and receive was demonstrated at X-band in real time against live targets. A performance analysis, including comparison to the Cramer-Rao bounds, is given for the coherence parameter estimators during the presentation. Future plans are briefly discussed, including experiments with more radar channels and plans to demonstrate additional benefits of using MIMO techniques with distributed apertures and through spatial - - diversity