JP4625720B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that detects a target on a time-frequency axis.

  As is well known, in a radar apparatus, a video signal based on a reflected echo from a target is Fourier transformed to obtain a spectrum on the frequency axis, and a target component is extracted by filtering the spectrum.

  For example, STFT (short-time Fourier transform, see Non-Patent Document 1) is used to detect a target signal having a spread on the time-frequency axis, such as a helicopter blade signal. In this detection method, STFT is performed on a signal in which clutter is suppressed by MTI (moving target indicator; see Non-Patent Document 2), and CFAR (constant false alarm rate; Constant False on the time axis) is performed. The target is detected by applying Alarm Rate (see Non-Patent Document 3) and comparing it with a predetermined threshold.

However, the conventional radar apparatus as described above has a problem in that when there is a clutter signal in which clutter remains locally on the time-frequency axis, a false detection occurs and a false alarm is generated. In order to prevent this, conventionally, a method has been proposed in which correlation is made with adjacent cells on the time axis and the frequency axis, and if there is a spread, it is rejected as clutter. However, adding such a correlation process increases the scale of the arithmetic processing and cannot efficiently detect the target.
Short-time Fourier transform, Sugawara, “Wavelet Beginners”, Tokyo Denki University Press, pp.23-24 MTI, IEICE, “Revised Radar Technology”, pp.67-70 CFAR (constant false alarm rate), Sekine, "Radar signal processing technology", IEICE, pp.96-106 (1991) Nakano et al., “Signal processing and image processing using wavelets”, Kyoritsu Publishing Co., Ltd., pp.49-70, pp.101-110 (1999) Japanese Patent Application No. 2004-193005 Japanese Patent Application No. 2005-039488.

  In the conventional radar apparatus described above, there is a problem that a false alarm is detected by the residual clutter component when detecting a target signal having a spread on the time-frequency axis. To prevent this, the spread of the clutter is detected. There is a problem that the correlation processing is necessary to increase the processing scale.

  The present invention has been made to solve the above problems, and provides a radar apparatus that reduces false alarms caused by clutter or the like by a simple method by utilizing the fact that the target signal has a spread on the time-frequency axis. For the purpose.

  In order to achieve the above object, the radar apparatus according to the present invention performs MTI processing as necessary, performs STFT or wavelet conversion to convert it to the time frequency axis, and then applies CFAR as necessary. If a cell having a value is detected and the M cell exceeds the threshold among the N cells around it, the detection is increased, or N around the cell selected around the maximum value to a plurality of extreme values is selected. Target detection is performed when M cells out of the cells exceed the threshold.

  In the radar apparatus having the above-described configuration, since the target signal has a spread, N cells in a predetermined range around the maximum value are determined, and it is determined whether or not the threshold is exceeded by more than M cells. The signal and clutter signal can be discriminated, and only the target signal can be detected. Furthermore, if the MTI process and the CFAR process are used together, the clutter after each process is more effective because it is difficult to spread on the time-frequency axis.

  As described above, the radar apparatus according to the present invention can increase the ability to detect a target signal having a spread on the time-frequency axis while reducing false alarms in a clutter environment. Therefore, according to the present invention, it is possible to provide a radar apparatus that reduces false alarms caused by clutter or the like by a simple method by utilizing the spread of the target signal on the time-frequency axis.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a functional block diagram showing an embodiment of a radar apparatus according to the present invention. In FIG. 1, a received signal obtained by capturing a reflected echo from a target is supplied to an MTI processing unit 11, where MTI processing is performed and clutter components are suppressed. This MTI processing output is supplied to the STFT processing unit 12, where signals of F0 to Fn-1 banks on the frequency axis are extracted. These bank signals are supplied to the CFAR processing unit 13.

  The CFAR processing unit 13 is configured to suppress the occurrence of erroneous target detection due to clutter components or the like, and is specifically configured as shown in FIG. In FIG. 2, the input CFAR signal Xi is delayed by the delay circuit 131 and then distributed to the adder circuit 132 and the divider circuit 134. The adding circuit 132 adds N delay signals over a certain period, and the addition result is input to the averaging processing circuit (1 / N) 133, and the N average value of the addition result is calculated. This N average value is input to the division circuit 134. The division circuit 134 obtains a division result of the delay signal and the N average value, and uses this as the CFAR output.

  The CFAR output is sent to the maximum value detector 14, where the maximum value is detected. At this time, the number of cells exceeding the thresholds 151 to 15n (predetermined determination cell range) among the N cells around the maximum value is determined, and the number of cells exceeds M in the M / N detection unit 16. In the following, detection is given. Hereinafter, the target component is detected from the detection result.

  In the above configuration, the processing operation will be described below with reference to FIGS.

First, FIG. 3 shows the state of input data. As shown in FIG. 3A, the radar transmission / reception data is data of a range cell × PRI (pulse repetition interval; R × L cell), which is shown for each range as shown in FIG. 3B. And input as a signal (blade signal) for each PRI. As shown in FIG. 1, an MTI process (11) is performed on the input signal to suppress clutter, and then an STFT process (12) is performed on the signal. By STFT processing, F (n / 2-1) to F0 to F (-n / 2) (n: PRI number of STFT processing) bank signals are obtained on the frequency axis. Thus, the number of K cells is obtained, and thus converted data of frequency axis × time axis = n × K is obtained.
K = {L-n (1-p0)} / n (1-p0)
here,
L: Total number of PRIs
n: Number of STFT pulses
p0: Overlap ratio at STFT CFAR (13) having the configuration shown in FIG. 2 is performed on the signal on the time-frequency axis. As the axis of the CFAR, the target signal is prevented from being suppressed as an axis different from the direction in which the target signal has a spread. For the result of the CFAR processing, a maximum value cell is extracted (14), and detection is performed when M cells out of the surrounding N cells (Gp × Gq) exceed the threshold (151 to 15n). (16).

  FIG. 4 shows how the body is suppressed by MTI processing when the ground clutter or the target is a helicopter. FIG. 4A shows the frequency distribution before MTI and FIG. 4B shows the frequency distribution after MTI. As can be seen from this figure, the fuselage or ground clutter remaining before the MTI is almost completely suppressed by the MTI processing.

  FIG. 5 further shows how weather clutter is suppressed when CFAR processing is applied. In the figure, residual clutter components exist after CFAR processing, but all remain in a single cell. As shown in the figure, among N = Gp × Gq cells around the maximum value, when the threshold is exceeded by more than M cells, it is detected as a target.

  Therefore, according to the radar apparatus having the above configuration, in the clutter environment, it is possible to increase the ability to detect a target signal having a spread on the time frequency axis while reducing false alarms.

  The present invention is characterized in that after converting to the time-frequency axis by STFT processing, the maximum value is detected, and when the threshold is exceeded in the M cells among the surrounding N cells, it is detected as a target. The present invention can also be applied when there are no other processes such as MTI processing and CFAR processing.

  Further, instead of MTI processing, a type in which clutter is suppressed by another frequency filter may be used.

  In the above embodiment, the cell around the maximum value is selected for the output after CFAR, but the extreme value is detected on the time-frequency axis, and the cell is centered on the extreme value from the maximum value to a plurality of extreme values. By selecting, a system that can detect up to a plurality of targets may be used.

  Further, instead of the STFT, it may be converted into a time-frequency axis by wavelet transform (see Patent Document 1 and Non-Patent Document 4), and the same processing as in the case of the STFT may be performed.

  Furthermore, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Moreover, you may combine the component covering different embodiment suitably.

The functional block diagram which shows one Embodiment of the radar apparatus concerning this invention. The functional block diagram which shows the specific structure of the CFAR process part of FIG. The schematic diagram for demonstrating about the input signal input into the MTI processing part of FIG. The schematic diagram for demonstrating the processing content of the MTI processing part of FIG. The schematic diagram which shows a mode that a weather clutter is suppressed in the CFAR process part of FIG.

Explanation of symbols

11 ... MTI processing unit,
12 ... STFT processing unit,
13 ... CFAR processing unit,
131 ... delay circuit,
132... Addition circuit,
133: Averaging processing circuit (1 / N),
134: division circuit,
14 ... maximum value detection unit,
151-15n ... threshold,
16: M / N detector.

Claims (12)

In a radar apparatus for detecting a target from a received signal having a target signal having a spread on a time-frequency axis,
A time frequency axis converting means for converting the target signal into a time frequency axis by performing a short time Fourier transform (STFT);
Maximum value cell detection means for detecting a cell of the maximum value of the time frequency axis from the target signal subjected to the time frequency axis conversion;
A radar apparatus comprising: target detection means for detecting a target when M (N ≧ M) cells out of the N cells around the maximum value cell exceed a threshold.   The radar apparatus according to claim 1, further comprising a moving target detection unit that is disposed upstream of the time-frequency axis conversion unit and that performs clutter suppression processing on the target signal.   2. The apparatus according to claim 1, further comprising a CFAR processing unit that performs a CFAR (Constant False Alarm Rate) process on the conversion output of the time-frequency axis conversion unit and outputs the result to the maximum value cell detection unit. The radar apparatus described. In a radar apparatus for detecting a target from a received signal having a target signal having a spread on a time-frequency axis,
A time frequency axis converting means for converting the target signal into a time frequency axis by performing a short time Fourier transform (STFT);
A cell selecting means for detecting an extreme value on the time frequency axis from the target signal subjected to the time frequency axis conversion, and selecting a cell centering on a maximum value to a plurality of extreme values;
Target detection means for increasing target detection when M (N ≧ M) cells exceed the threshold among N cells around the cells selected around the maximum value to a plurality of extreme values. A radar device characterized by:   5. The radar apparatus according to claim 4, further comprising a moving target detection unit that is disposed upstream of the time-frequency axis conversion unit and that performs clutter suppression processing on the target signal. 5. The apparatus according to claim 4, further comprising a CFAR processing unit that performs a CFAR (Constant False Alarm Rate) process on the conversion output of the time-frequency axis conversion unit and outputs the result to the cell selection unit . Radar device. In a radar apparatus for detecting a target from a received signal having a target signal having a spread on a time-frequency axis,
A time-frequency axis conversion means for converting the target signal into a time-frequency axis by wavelet transform;
Maximum value cell detection means for detecting a cell of the maximum value of the time frequency axis from the target signal subjected to the time frequency axis conversion;
A radar apparatus comprising: target detection means for detecting a target when M (N ≧ M) cells out of the N cells around the maximum value cell exceed a threshold.   The radar apparatus according to claim 7, further comprising a moving target detection unit that is disposed upstream of the time-frequency axis conversion unit and that performs a clutter suppression process on the target signal.   8. The apparatus according to claim 7, further comprising: a CFAR processing unit that performs a CFAR (Constant False Alarm Rate) process on the conversion output of the time-frequency axis conversion unit and outputs the result to the maximum value cell detection unit. The radar apparatus described. In a radar apparatus for detecting a target from a received signal having a target signal having a spread on a time-frequency axis,
A time-frequency axis conversion means for converting the target signal into a time-frequency axis by wavelet transform;
A cell selecting means for detecting an extreme value on the time frequency axis from the target signal subjected to the time frequency axis conversion, and selecting a cell centering on a maximum value to a plurality of extreme values;
Target detection means for increasing target detection when M (N ≧ M) cells exceed the threshold among N cells around the cells selected around the maximum value to a plurality of extreme values. A radar device characterized by:   The radar apparatus according to claim 10, further comprising a moving target detection unit that is disposed upstream of the time-frequency axis conversion unit and that performs a clutter suppression process on the target signal. 11. The apparatus according to claim 10, further comprising CFAR processing means for performing a CFAR (Constant False Alarm Rate) process on the conversion output of the time-frequency axis conversion means and outputting the result to the cell selection means . Radar device.

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