Adaptive MTD digital processor for surveillance radar

Claim 2

In a surveillance radar provided with a coherent video detector and with a signal extractor, the combination therewith of a digital MTD processor inserted between said video detector and said signal extractor, said processor comprising: an analog/digital converter connected to said video detector; a multiplicity of Doppler filters with inputs connected in parallel to said converter; evaluation means disposed between said filters and said signal extractor; environment-responsive sensing means for registering clutter distribution for the area surveyed by the radar; and modification means controlled by said sensing means for varying the characteristics of said filters in accordance with clutter conditions prevailing in different regions of the surveyed area, said modification means comprising a plurality of selectors respectively associated with said filters for loading same with one of several stored sets of predetermined weights depending on clutter density, said sensing means including a clutter map controlling said selectors, said filters including a zero filter, said sensing means comprising ground-clutter-measuring means connected to the output of said zero filter for updating said clutter map, wherein said sets include sets of weights being three sets W A , W B , W C stored in every selector, set W A pertaining to regions of no ground clutter, set W B pertaining to regions of light to moderate ground clutter, set W C pertaining to regions of heavy ground clutter.

Claim 3

The combination defined in claim 1, further comprising switch means responsive to said sensing means for disconnecting said zero filter from said evaluation means during surveillance of regions of heavy ground clutter.

Claim 4

The combination defined in claim 1 wherein said evaluation means comprises a multiplicity of modulus extractors respectively connected to the outputs of said filters, a multiplicity of threshold circuits respectively connected to the outputs of said modulus extractors, and logical summing means interposed between the outputs of said threshold circuits and said signal extractor.

Claim 5

The combination defined in claim 3 wherein each of said threshold circuits comprises a fixed-threshold comparator and an adaptive-threshold comparator, connected in parallel to the output of the respective modulus extractor, and switchover means for alternatively connecting the outputs of said comparators to said summing means, said sensing means including a rain-clutter map controlling said switchover means for excluding said adaptive-threshold comparator during surveillance of regions of low and zero rainfall.

Claim 6

The combination defined in claim 4 wherein said threshold circuits are provided with threshold modifiers responsive to commands from said signal extractor for changing the threshold levels of said comparators in a manner tending to maintain a constant false-alarm rate.

Claim 7

The combination defined in claim 1 wherein, with k Doppler filters besides said zero filter and k at most equal to seven, each set contains eight weights represented by as many complex numbers with real coefficients W R and imaginary coefficients W I , the values of said coefficients having ratios substantially corresponding to those of the first k columns of the following Tables I, II and III: TABLE I __________________________________________________________________________ FILTER #1 FILTER #2 FILTER #3 FILTER #4 FILTER #5 FILTER #6 FILTER #7 W.sub.A W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I __________________________________________________________________________ 1 -21 -21 0 -30 21 -21 30 0 21 21 0 30 -21 21 2 0 -65 65 0 0 65 -65 0 0 -65 65 0 0 65 3 72 -72 0 102 -72 -72 102 0 -72 72 0 -102 72 72 4 127 0 -127 0 127 0 -127 0 127 0 -127 0 127 0 5 90 90 0 -127 -90 90 127 0 -90 -90 0 127 90 -90 6 0 102 102 0 0 -102 -102 0 0 102 102 0 0 -102 7 -46 46 0 65 46 46 65 0 46 -46 0 -65 -46 -46 8 -30 0 -30 0 -30 0 -30 0 -30 0 -30 0 -30 0 __________________________________________________________________________ TABLE II __________________________________________________________________________ FILTER # 1 FILTER #2 FILTER #3 FILTER #4 FILTER #5 FILTER #6 FILTER #7 W.sub.B W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I __________________________________________________________________________ 1 -7 -27 24 11 11 -20 21 0 11 20 24 -11 -7 22 2 51 -17 -33 58 57 14 -62 0 57 -14 -33 -58 51 32 3 75 71 -99 -62 -87 54 102 0 -87 -54 -99 62 75 -71 4 -65 114 82 -127 28 -127 -127 0 28 127 82 127 -65 -114 5 -126 -35 127 81 68 112 127 0 68 -112 127 - 81 -126 35 6 2 -103 -63 98 -101 -24 -102 0 -101 24 -63 -98 2 103 7 59 -14 -55 -39 50 -31 62 0 50 31 -55 39 59 14 8 11 21 17 -20 -40 22 -21 0 -40 -22 17 20 11 -21 __________________________________________________________________________ TABLE III __________________________________________________________________________ FILTER # 1 FILTER #2 FILTER #3 FILTER #4 FILTER #5 FILTER #6 FILTER #7 W.sub.C W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I W.sub.R W.sub.I __________________________________________________________________________ 1 0 15 -11 10 12 3 12 0 12 -3 -11 -10 0 -15 2 -36 -9 -30 -41 -39 23 -44 0 -39 -23 -30 41 -36 9 3 18 -60 85 -46 21 -92 91 0 21 92 85 46 18 60 4 76 24 48 123 92 109 -127 0 72 -109 48 -123 76 -24 5 -24 76 -127 33 -127 -25 127 0 -127 25 -127 - 33 -24 -76 6 -60 -20 -12 -94 76 -53 -91 0 76 53 -12 94 -60 20 7 14 -35 49 0 -8 45 44 0 -8 -45 49 0 14 35 8 12 9 -2 15 -7 -10 -12 0 -7 10 -2 15 12 -9 __________________________________________________________________________

Claim 8

The combination defined in claim 6 wherein said zero filter has eight weights with zero imaginary coefficients W I and with real coefficients W R having ratios substantially equaling 18:53:96:127:127:96:53:18.