This program proposes to study, develop, simulate, fabricate and test a ground based receiver-signal processor system architecture capable of detecting, measuring the angle of arrival and uniquely identifying the emissions of a modern LPI radar altimeter. The basis for the program is the use of high probability of intercept receiver technology to scan wide frequency ranges in msec time periods with sensitivity, when combined with a low gain DF antenna, of at least -118 dBmi. This acquisition receiver will be integrated with digital receiver/processor technology to provide paremeter and direction measurements to identify the signal type and direction. Monitoring and control of modern cellular and satellite LPI type narrow and wide band mobile communications signals.