Point clutter threshold determination for radar systems

Claim 2

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values; and means for inhibiting detection when more than one of said first, second and third values exceeds a predetermined saturation limit.

Claim 3

The threshold system of claim 1 including means for setting the combined value equal to the largest of said first, second and third value.

Claim 4

The threshold system of claim 1 including means for setting the combined value equal to a power summation of the first, second and third values.

Claim 5

The threshold system of claim 1 including means for setting the combined value equal to a voltage summation of the first, second and third values.

Claim 6

The threshold system of claim 3 including means for weighting the first, second and third values before summation.

Claim 7

The threshold system of claim 4 including means for weighting the first, second and third values before summation.

Claim 8

The threshold system of claim 1 including means for angularly spacing apart said first and third directions by approximately the 6 dB two-way beamwidth of the radar antenna.

Claim 9

The threshold system of claim 1 including means for separately obtaining said first, second and third values from three adjacent coherent processing intervals of the radar.

Claim 10

The threshold system of claim 2 wherein the controlling means includes means for setting the threshold level at a fixed predetermined amount of attenuation below the largest of the first, second and third values, and means for indicating an alarm when clutter residue exceeds said threshold level.

Claim 11

The threshold system of claim 1 including means for providing data representative of the present clutter signal, and wherein said controlling means further includes means using said data about the present clutter signal to change the threshold level established by the first, second and third values.

Claim 12

The threshold sytem of claim 10 wherein the radar is a moving target detector radar system, and including a zero doppler filter which provides the data representative of the present clutter signal.

Claim 13

The threshold system of claim 10 wherein the radar is a moving target indicator radar system including means for generating present input echo data, and including means for providing the present input echo data as the data representative of the present clutter signal.

Claim 14

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for changes in the scan rate of the radar antenna system.

Claim 15

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for changes in the scan rate of the radar antenna system.

Claim 16

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for changes in the interpulse period of the radar.

Claim 17

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for changes in the interpulse period of the radar.

Claim 18

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for the variable interpulse period in a moving target indicator radar system.

Claim 19

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection threshold level for the variable interpulse period in a moving target indicator radar system.

Claim 20

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection clutter threshold level for radar instability.

Claim 21

An adaptive detection threshold system for a radar having a scanning antenna system, said threshold system comprising: means for obtaining data corresponding to the amplitude of clutter signals received by the radar for different azimuths of the radar antenna; means for selecting at least first, second and third values of said data, with said first value being representative of the clutter amplitude received by the radar when its antenna is positioned in a first direction, said second value being representative of the clutter amplitude received by the radar when its antenna is positioned in a second direction, and said third value being representative of the clutter amplitude received by the radar when its antenna is positioned in a third direction, said second direction being located angularly between said first and third directions; means for combining said first, second and third values; and means for controlling the detection threshold level for signals received when the radar antenna is in said second direction, with the controlling means being dependent upon a combined value derived from combining said first, second and third values, said controlling means including means for compensating the detection clutter threshold level for radar instability.

Claim 22

The threshold system of claim 1 wherein the means for controlling the detection threshold level includes means for power combining the largest of said first, second and third values with at least one other compensation signal value.

Claim 23

The threshold system of claim 17 including means for deriving said one other compensation signal value from conventional constant false alarm rate signal processing.

Claim 24

An adaptive detection threshold system for a moving target detector radar having a scanning antenna system, said threshold system comprising the combination of: a clutter map containing integrated values corresponding to the mean amplitude of echo signals received by the radar for different azimuths of the radar antenna; means for comparing three clutter map values corresponding to first, second and third adjacent azimuth locations of the map, with said second azimuth location being between said first and third azimuth locations, and said comparing means providing a first residue estimate value equal to the largest of said three map values at a time when the radar is obtaining new echo signal data for the second azimuth location; means for providing a second clutter residue estimate value derived from said new echo signal data; means for compensating the second clutter residue estimate value for changes in the scan rate of the radar antenna system; means for providing a third clutter residue estimate value derived from conventional constant false alarm rate signal processing; means for combining the first, second and third clutter residue estimate values to provide an estimated interference value; means for adding a fixed value to said estimated interference value to obtain a combined threshold value; and means for inhibiting the signalling of an alarm when more than one of the clutter map values exceeds a saturation limit.

Claim 25

An adaptive detection threshold system for a moving target detector radar having a scanning antenna system, said threshold system comprising the combination of: a clutter map containing integrated values corresponding to the mean amplitude of echo signals received by the radar for different azimuths of the radar antenna; means for comparing three clutter map values corresponding to first, second and third adjacent azimuth locations of the map, with said second azimuth location being between said first and third azimuth locations, and said comparing means providing a first residue estimate value equal to the largest of said three map values at a time when the radar is obtaining new echo signal data for the second azimuth location; means for providing a second clutter residue estimate value derived from said new echo signal data; means for compensating the second clutter residue estimate value for changes in the scan rate of the radar antenna system; means for providing a third clutter residue estimate value derived from conventional constant false alarm rate signal processing; means for combining the first, second and third clutter residue estimate values to provide an estimated interference value; means for adding a fixed value to said estimated interference value to obtain a combined threshold value; and means for inhibiting the signalling of an alarm when more than one of the clutter map values exceeds a saturation limit.

Claim 26

The threshold system of claim 19 including means for generating values corresponding to said first, second and third azimuth locations spaced in time a total time period which is approximately equal to the time required for the antenna system to scan across its 6 dB two-way beamwidth.

Claim 29

The method of claim 21 wherein the three azimuths provide data over a time period which is approximately equal to the time period required for the antenna to scan a distance equal to its 6 dB beamwidth.

Claim 30

The method of claim 21 including the step of adjusting the established threshold level based upon current echo data from a zero doppler filter.

Claim 31

The method of claim 21 including the step of adjusting the established threshold level based upon data from constant false alarm rate processing.