SPATIALLY DIVERSE COHERENT ARRAYS FOR SPACE BASED RADAR

A NEW CLASS OF ARRAY CALLED THE SPATIALLY DIVERSE COHERENT ARRAY (SDCA) IS PROPOSED FOR STUDY. SUCH ARRAYS USE A NEW CONCEPT INTRODUCED HERE--THE SIMULTANEOUS TRANSMISSION OF INDEPENDENT WAVEFORM FROM DIFFERENT CONFIGURATIONS OF ELEMENTS COMPRISING THE ARRAY. WHEN COMBINED COHERENTLY ON RECEIVE VIA ADAPTIVE SPACE-TIME PROCESSING, THE (SDCA) WITH IT'S ADDITIONAL SPATIAL DEGREES OF FREEDOM (DOF) PROVIDES A SIGNIFICANT INCREASE IN THE EFFECTIVE APERTURE OVER WHAT IS AVAILABLE WITH A SINGLE TRANSMIT BEAM. SBR APPLICATION - RADARS IN ORBIT OFTEN REQUIRE MULTIPLE DOF ON RECEIVE IN ORDER TO DETECT LOW SPEED TARGETS IMBEDDED IN MAINBEAM CLUTTER. THESE DOF TYPICALLY TAKE THE FORM OF SUB-ARRAYS FOR CORPORATE FEED ANTENNAS OR OVERLAPPING RECEIVE BEAMS WITH SPACE FED LENS ARRAYS. OPTIMUM ADAPTIVE SPACE-TIME PROCESSING (A GENERALIZATION OF DPCA) STILL RESULTS IN LOSSES FOR LOW VELOCITY TARGETS RESULTING IN MINIMUM DETECTABLE TARGET VELOCITIES MDV THAT ARE INVERSELY PROPORTIONAL TO THE APERTURE SIZE. ANALYSIS INDICATES THAT THE SDCA INCREASES THE EFFECTIVENESS APERTURE BY 40% RESULTING IN A 40% REDUCTION IN THE MDV. A SDCA WITH ONLY TWO SIMULTANEOUS TRANSMIT BEAMS, EACH WITH A DIFFERENT CODING, AND TWO RECEIVE BEAMS, ALLOWS DE-COUPLING OF 4 ROUND TRIP PATHS. SUCH A SYSTEM HAS A LOWER MDV THAN A FULLY ADAPTIVE ARRAY WITHOUT SPATIAL DIVERSITY.