Target detection system and method
Some embodiments are directed to methods of detecting a target that include: receiving signals reflected from a target of interest, the signals having a bandwidth large enough to provide a plurality of range cells along an expected target, and processing the received signal(s) by (i) determining the phases of contiguous groups of range cells, the group size selected to approximate to sizes of targets of interest, (ii) phase-shifting the returns within a group to increase constructive interference and thereby signal power; and (iii) combining the phase shifted returns to produce phase-adjusted combined returns, and performing a detection on those combined returns. Some embodiments may provide enhanced target detection capabilities. The process may be repeated for different potential target sizes, and may be performed either on real time data, or off-line on recorded data, and is applicable to both radar and sonar.
1. A system comprising:
an antenna; and
a receiver and a processor,
wherein the antenna is configured to receive signals reflected from potential targets of interest, the signals having a bandwidth large enough to provide a range resolution smaller than a largest dimension of the target of interest, the receiver is configured to demodulate the signals and generate a set of high range resolution (HRR) returns each containing phase and amplitude information associated with the signals from a particular range cell, and pass the information to the processor, wherein the processor is configured to detect a target of interest by processing the HRR returns by:
i) grouping HRR returns contiguously by range, each group containing a plurality of range cells covering a total range spread of similar dimension to a target type of interest;
ii) processing the HRR returns within a group to determine their phases;
iii) phase-shifting the HRR returns within a group to increase constructive interference between the HRR returns, and composite power therein, as compared to non-phase shifted returns; and
iv) combining the phase shifted HRR returns to produce phase-adjusted combined returns of increased amplitude, and performing a detection using those combined returns to detect the target.
2. The system according to claim 1 , the processor being further configured to repeat steps (i) to (iv) using different group sizes (range spreads) to cover multiple target sizes.
3. The system according to claim 1 , the processor being further configured to repeat steps (i) to (iv) using a sliding window to accommodate and detect targets that would otherwise straddle in range boundaries of the groups, without any need to receive further signals.
4. The system according to claim 1 , further configured to combine the HRR returns grouped in step (i) to form low range resolution (LRR) unprocessed returns, and configured to perform a detection on the unprocessed returns.
5. The system according to claim 4 , further configured to carry out the detection on the unprocessed combined return using a constant false alarm rate (CFAR) processing algorithm.
6. The system according to claim 1 , processor being further configured to perform the combining step by summing the returns.
7. The system according to claim 1 , further configured to multiply the grouped returns by a windowing function.
8. The system according to claim 1 , further configured to carry out the detection on the phase-adjusted combined returns using a constant false alarm rate (CFAR) processing algorithm.
9. The system according to claim 1 , further configured to process, under step (ii), utilizing information based on one of:
(i) the Doppler frequency corresponding to the most powerful signal in the frequency domain within the group,
(ii) a composite measure of the signal power in the frequency domain in a plurality of range cells within the group,
(iii) pre-existing knowledge of the likely velocities of potential target types,
(iv) the formation and analysis of a velocity history for each potential target, or
(v) a combination of the above,
and further configured to select a Doppler bin that is most likely to contain the target and determine the phase adjustment for particular returns.
10. The system according to claim 9 , further configured to determine the phases of the HRR returns in each of the HRR range cells for the selected Doppler frequency bin within a particular block using Fourier analysis to determine complex components of the corresponding frequency domain signals.
11. The system according to claim 1 , further configured to utilize Fourier analysis in the processing to convert the signals to the frequency domain, to generate range-Doppler information.
12. The system according to claim 1 , further configured to calculate a separate phase angle for each range cell in each group of HRR range cells.
13. The system according to claim 12 , further configured to adjust each HRR time domain return in each group by the phase angle for the corresponding range cell.
14. The system according to claim 13 , further configured to determine the phase adjustment for the HRR returns within each range cell as the phase angle of a Doppler bin for that range cell.
15. The system according to claim 1 , wherein the antenna is configured to receive the signal and to provide it to the receiver, and said received signal is a reflection from a target of a signal transmitted by an independent transmitter that does not co-operate with the receiver.
16. The system according to claim 1 , wherein the system further incorporates a signal source and transmitter, for generating and transmitting a signal, the bandwidth of the signal being large enough to provide a range resolution smaller than a largest estimated dimension of the target of interest.
17. The system according to claim 16 , wherein the transmitted signals are one of: electromagnetic signals, and acoustic signals.
18. The system according to claim 1 , further configured to combine the phase shifted HRR returns of step (iii) within each group to produce phase-adjusted combined returns for that group, and to process the phase-adjusted combined returns from a plurality of groups to detect the presence of targets.