Demonstration of an Adaptive, Coherent-Combining Laser Radar Receiver

The first demonstration of an adaptive, coherent-combining cw laser radar receiver is described. It consists of two independent aperture/coherent detectors whose IFs are electro-optically co-phased in real time and then summed. This results in approximately a 2x increase in the carrier-to-noise (CNR) ratio, and a reduction by ½ of the carrier fading strength or normalized CNR variance. The “two-element” system was field tested and operated in accord with theory. The construction of an “8-element” system is about completed. The eight electro-optical phase locked loops can “phase-lock” signals with an input dynamic range of 58dB and with a phase error of only 6.2 degrees at a phase fluctuation rate of 5 kHz.