Screening system and method
A radar screening system that detects an object in a region of interest by transmitting coded signals having a first polarization and receiving coded return signals having at least a second polarization. Suitably the transmitted signals have one polarization and some return signals have the same polarization and other return signals have an orthogonal polarization. The return signals are processed into voxels to calculate at least a cross-polar value at each voxel. Voxels are identified as being from an object of interest if an indicator using at least the cross-polar value exceeds a threshold. Preferably the indicator uses at least a ratio of the cross-polar value and the co-polar value. The radar screening system may also perform automatic target recognition by taking into account shape and location of the object of interest.
1. A radar screening system for detecting an object in a region of interest comprising:
at least one radar array, said at least one radar array including:
a plurality of transmitter elements that transmit a plurality of differently coded signals toward the object, the coded signals having at least a first polarization; and
a plurality of receiver elements that receive a plurality of coded return signals reflected from the object, the coded return signals having at least a second polarization orthogonal to the first polarization; and
at least one processor coupled to the plurality of transmitter elements and the plurality of receiver elements, said at least one processor being adapted to:
decode the plurality of coded return signals reflected from the object;
extract from the decoded plurality of coded return signals a multiplicity of captured signals for each transmitter to receiver path;
align the multiplicity of captured signals to be substantially time and phase coincident for each voxel in a region of interest;
sum the aligned captured signals for each voxel in the region of interest;
calculate at least a cross-polar value at each voxel; and
identify a voxel as from an object of interest if an indicator calculated using at least the cross-polar value exceeds a threshold.
2. The radar screening system of claim 1 wherein the receiver elements comprise first receiver elements that receive a plurality of coded return signals reflected from the object that have a polarization orthogonal to the first polarization and second receiver elements that receive a plurality of coded return signals reflected from the object that have the same polarization as the first polarization.
3. The radar screening system of claim 1 wherein the transmitter elements comprise first transmitter elements that transmit a plurality of coded signals that have a first polarization and second transmitter elements that transmit a plurality of coded signals that have a polarization orthogonal to the first polarization.
4. The radar screening system of claim 1 wherein the transmitter elements comprise first transmitter elements that transmit a plurality of coded signals that have a first polarization and second transmitter elements that transmit a plurality of coded signals that have a second polarization orthogonal to the first polarization, and the receiver elements comprise first receiver elements that receive coded return signals having a polarization orthogonal to the first polarization and coded return signals having a polarization parallel to the first polarization and second receiver elements that receive coded return signals having a polarization orthogonal to the second polarization and coded return signals having a polarization parallel to the second polarization.
5. The radar screening system of claim 4 wherein the first transmitter elements and the second transmitter elements are the same elements with the coded signals that have a first polarization and the coded signals that have a second polarization being transmitted at different times.
6. The radar screening system of claim 4 wherein the first receiver elements and the second receiver elements are the same elements.
7. The radar screening system of claim 1 wherein the processor calculates an indicator being the ratio of co-polar values and cross-polar values in each voxel of the image.
8. The radar screening system of claim 1 wherein the first polarization and second polarization are linear polarizations.
9. The radar screening system of claim 1 wherein the first polarization and second polarization are right and left circular polarization.
10. The radar screening system of claim 1 wherein; the first polarization and second polarization are elliptical and are orthogonal.
11. The radar screening system of claim 1 wherein a voxel identified as from an object of interest, based on a ratio of cross-polar and co-polar signals forming that voxel, is highlighted on a representative image of a person and/or an alarm is raised.
12. The radar screening system of claim 1 wherein the transmitter elements and receiver elements are horn antennas.
13. The radar screening system of claim 1 wherein the transmitter elements and receiver elements are patch antennas.
14. The radar screening system of claim 1 wherein the processor is further adapted to analyze voxels identified as from an object of interest and determine shape of the object of interest.
15. The radar screening system of claim 1 wherein the processor is further adapted to analyze voxels identified as from an object of interest and determine location of the object of interest.
16. The radar screening system of claim 1 wherein the processor is further adapted to perform automatic target recognition of the object of interest based on analysis of a ratio of cross-polar and co-polar signals; a shape of the object of interest determined from analysis of yokels identified as from the object of interest; and location of the object of interest determined from analysis of voxels identified as from the object of interest.
17. The radar screening system of claim 16 wherein the processor generates an alarm when the object of interest is identified and/or assigns a risk level to the identified object of interest.
18. The radar screening system of claim 16 wherein the object of interest is tracked in time and the signals are processed in the manner of Inverse Synthetic Aperture Radar (ISAR).
19. The radar screening system of claim 1 wherein the processor is further adapted to subtract aligned captured signals obtained from a region of interest without a target present from aligned captured signals obtained from a region of interest with a target present.
20. A method of detecting an object in a region of interest including the steps of:
transmitting a plurality of differently coded signals toward the object, the coded signals having at least a first polarization;
receiving a plurality of coded return signals reflected from the object, the coded return signals having at least a second polarization orthogonal to the first polarization;
decoding the plurality of coded return signals reflected from the object;
extracting, from the decoded plurality of coded return signals a multiplicity of captured signals for each transmitter to receiver path;
aligning the multiplicity of captured signals to be substantially time and phase coincident for each voxel in a region of interest;
summing the aligned captured signals for each voxel in the region of interest;
calculating at least a cross-polar value at each voxel; and
identifying a voxel as from an object of interest if an indicator calculated using at least the cross-polar value exceeds a threshold.