AUTO MATIC DIRECTION FINDING FOR SPREAD SPECTRUM COMMUNICATIONS

AUTOMATIC DIRECTION FINDING ON UHF COMMUNICATION FREQUENCIES IS AN ESSENTIAL MILITARY CAPABILITY NOW PERFORMED BY TUNING A RECEIVER TO THE COMMUNICATION FREQUENCY AND OBTAINING A SINE/COSINE COMPONENT OF THE OUTPUT OF DIRECTIONAL ANTENNAS WHICH, WHEN COMPARED, PROVIDE THE BEARING TO THE TARGET. THIS TECHNIQUE IS NOT APPLICABLE TO MODERN SPREAD SPECTRUM AND FREQUENCY HOPPING RADIOS. THERE IS A NEED TO DEVELOP AN ARDF CAPABILITY AGAINST FREQUENCY HOPPERS. DSI PROPOSES TO OBTAIN DF BY USING A DUAL CHANNEL PULSE COMPRESSOR RECEIVER ON THE TWO AMPLITUDE/PHASE COMPARISON ANTENNA OUTPUTS AND COMPUTING BEARING ON-THE-FLY FOR EACH SWEEP OF THE SAW PULSE COMPRESSION FILTERS. DSI HAS BUILT SINGLE CHANNEL EXTREMELY HIGH SWEEP RATE PC RECEIVERS. THE 225-400 MHZ UHF BAND (WITH 25 KHZ CHANNEL RESOLUTION) CAN BE SWEPT AT A RATE HIGH ENOUGH TO PROVIDE REVISIT RATES SUFFICIENT TO DETECT FREQUENCY HOPPERS EVEN IF THEY HAS VERY HIGH HOP RATES. IN PHASE I, DSI WILL PERFORM A FEASIBILITY STUDY AND WILL DESIGN AN ARDF SYSTEM THAT WILL WORK BOTH AGAINST STANDARD AND SPREAD SPECTRUM SIGNALS. IN PHASE II DSI WILL BUILD A BRASSBOARD SYSTEM.