Target detection system in a radar system employing main and guard channel antennas

Claim 2

In a radar system of the type including first and second antennas for receiving radar returns from targets including an airborne target to be detected and main and guard channels for providing respectively a main channel output in response to the radar returns received by said first antenna and a guard channel output in response to the radar returns received by said second antenna, an arrangement comprising: first means responsive to the main channel output and the guard channel output for providing a selected output only when effectively the ratio of the main channel output to the guard channel output exceeds a selected ratio threshold level; and second means responsive to said first means and to the outputs of said main and guard channels for providing a target indication signal either when said main channel output exceeds a selected main channel threshold level and the guard channel output is less than a selected guard channel threshold level or when the output of said main and guard channels respectively exceed said main and guard channel threshold levels and said first means provides said selected output.

Claim 3

The system as described in claim 1 wherein said guard channel threshold level is smaller than said main channel threshold level.

Claim 4

The system as described in claim 1 wherein said first antenna is a high gain narrow beamwidth antenna, and said second antenna is a low gain wide beamwidth antenna.

Claim 5

The system as described in claim 3 further including third means for generating said selected guard channel threshold level as a function of the background noise level in said guard channel, with said guard channel threshold level being greater than said background noise level in said guard channel.

Claim 6

The system as described in claim 4 further including fourth means for generating said selected main channel threshold level as a function of the background noise level in said main channel, with said main channel threshold level being greater than said background noise level in said main channel.

Claim 7

The system as described in claim 5 wherein said guard channel threshold level is smaller than said main channel threshold level.

Claim 8

The system as described in claim 1 wherein said first means include means for amplifying said guard channel output by a factor definable as K and comParing means for providing said selected output only when the unamplified main channel output exceeds the amplified guard channel output, or wherein said first means include means for attenuating said main channel output by said K factor and comparing means for providing said selected output only when the attenuated main channel output exceeds the unattenuated guard channel output.

Claim 9

The system as described in claim 7 wherein said first antenna is a high gain narrow beamwidth antenna, and said second antenna is a low gain wide beamwidth antenna.

Claim 10

The system as described in claim 8 further including third means for generating said selected guard channel threshold level as a function of the background noise level in said guard channel, with said guard channel threshold level being greater than said background noise level in said guard channel.

Claim 11

The system as described in claim 9 further including fourth means for generating said selected main channel threshold level as a function of the background noise level in said main channel, with said main channel threshold level being greater than said background noise level in said main channel.

Claim 12

The system as described in claim 10 wherein said guard channel threshold level is smaller than said main channel threshold level.

Claim 13

In an airborne radar system of the type including a main high gain narrow beamwidth antenna for transmitting radar signals reflected back as radar returns to said main antenna from an airborne target and from ground targets and a guard low gain wide beamwidth antenna for receiving radar returns from said targets, said system further including a receiver with a main channel for providing an output for radar returns received by said main antenna and a guard channel for providing an output for radar returns received by said guard antenna, an arrangement comprising: first means responsive to the main channel output for providing a true output only when said main channel output exceeds a selected main channel threshold level; second means responsive to the guard channel output for providing a true output only when said guard channel output exceeds a selected guard channel threshold level and for providing a false output when said guard channel output does not exceed said guard channel threshold level; third means responsive to the outputs of said main and guard channels for corresponding range-doppler cells for providing a true output only when effectively the ratio of the outputs of said channels exceeds a selected ratio threshold level; and fourth means responsive to the outputs of said first, second and third means for providing an airborne-target-indicating signal only when either the output of said first means is true and the second means output is false or when all the outputs of said first, second and third means are true.

Claim 14

In an airborne radar system of the type including a main high gain narrow beamwidth antenna for transmitting radar signals reflected back as radar returns to said main antenna from an airborne target and from ground targets and a guard low gain wide beamwidth antenna for receiving radar returns from said targets, said system further including a receiver with a main channel for providing an output for radar returns received by said main antenna and a guard channel for providing an output for radar returns received by said guard antenna, an arrangement comprising: first means responsive to the main channel output for providing a true output only when said main channel output exceeds a selected main channel threshold level; second means responsive to the guard channel output for providing a true output only when said guard channel output exceeds a selected guard channel threshold level and for providing a false output when said guard channel output does not exceed said guard channel threshold level; third means responsive to the outputs of said main and guard channels for corresponding range-doppler cells for providing a true output only when effectively the ratio of the outputs of said channels exceeds a selected ratio threshold level; and fourth means responsive to the outputs of said first, second and third means for providing an airborne-target-indicating signal only when either the output of said first means is true and the second means output is false or when all the outputs of said first, second and third means are true.

Claim 15

The system as described in claim 12 wherein the guard channel threshold level is less than the main channel threshold level.

Claim 16

The system as described in claim 12 wherein said main antenna pattern is characterized by a mainlobe with a gain definable as GML, and sidelobes including a sidelobe with a gain definable as GSL and said guard antenna pattern is characterized by a primary lobe with a gain definable as GG and said selected ratio threshold level is less than GML/GG and greater than GSL/GG.

Claim 17

The system as described in claim 12 further including fifth means for generating said guard threshold level as a function of the background noise level in said guard channel, with the guard threshold level being greater than said background noise level in said guard channel, and sixth means for generating said main threshold level as a function of the background noise level in said main channel with the main threshold level being greater than said background level in said main channel.

Claim 18

The system as described in claim 15 wherein said fifth means include a multiplier for multiplyinG the background noise level in said guard channel by a factor X and said sixth means include a multiplier for multiplying the background noise level in said main channel by a factor Y where Y > X.