JP2007057369A - Target detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a target detection device capable of detecting efficiently a target by using wavelet transformation even if an unnecessary wave component is included in an input signal, and reducing a circuit constitution or the scale of signal processing. <P>SOLUTION: This device is equipped with: a wavelet transformation circuit 11 for generating a plurality of wavelet development coefficients by performing discrete wavelet transformation of a signal from an antenna 10 transmitting/receiving a beam; a development coefficient selection circuit 12 for selecting a wavelet development coefficient used for detection of a target signal from among the plurality of generated wavelet development coefficients; a detector 14 for outputting a detection signal showing that the target signal is detected when the selected wavelet development coefficient is larger than a prescribed threshold level; and a detection control circuit 15 for setting PRI of a transmitted/received beam so that the target signal is included in the wavelet development coefficient having few unnecessary signals, and controlling the development coefficient selection circuit so that the wavelet development coefficient having few unnecessary signals and including the target signal is selected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a target detection apparatus that detects a target by being applied to a radar apparatus that searches or tracks a target or a reception apparatus that observes a signal waveform, and more particularly to a technique for detecting a target using wavelet transform.

  In recent years, wavelet transform is often used in the field of signal processing instead of Fourier transform and discrete cosine transform (DCT). Since the wavelet transform can efficiently process a signal whose intensity is locally distributed, it is applied in various fields such as image processing, audio signal processing, and video signal processing in a radar apparatus. The details of the wavelet transform are described in Non-Patent Document 1, for example.

  By the way, in a target detection apparatus applied to a conventional radar apparatus, a large SN ratio (signal power to noise power ratio) is required to detect a target signal representing a target that appears only instantaneously. However, when the target signal is small or the antenna gain of the radar apparatus is small, there is a problem that the target signal cannot be detected because the SN ratio is small. In addition, there is a problem that it is difficult to detect the target signal when an unnecessary wave component such as clutter is included in the received signal transmitted from the antenna.

  In order to solve such a problem, a radar apparatus is known that detects a target using wavelet transformation, focusing on the fact that wavelet transformation is highly sensitive to signal change points. FIG. 12 is a diagram showing a configuration of a conventional radar apparatus using such a wavelet transform. The radar apparatus includes a wavelet transform circuit 11, a development coefficient selection circuit 12, an inverse wavelet transform circuit 60, a CFAR (Constant False Alarm Rate) circuit 13, and a detector 14.

In this radar apparatus, wavelet expansion coefficients W1 to Wj generated by wavelet transforming input data in the wavelet conversion circuit 11 are sent to the expansion coefficient selection circuit 12. The expansion coefficient selection circuit 12 sends the expansion coefficient from which the expansion coefficient component that is expected to contain noise is removed to the inverse wavelet transform circuit 60. The inverse wavelet transform circuit 60 returns the given expansion coefficient component to the frequency component again and sends it to the CFAR circuit 13. The CFAR circuit 13 performs CFAR processing using the reconverted data sent from the inverse wavelet transform circuit 60 and sends it to the detector 14. The detector 14 performs target detection processing based on the signal from the CFAR circuit 13 and outputs a signal representing the detected target. Details of the CFAR processing performed in the CFAR circuit 13 are described in Non-Patent Document 2, for example.
Nakano et al., “Signal processing and image processing using wavelets”, Kyoritsu Publishing Co., pp. 49-70, pp. 101-110 (1999) Sekine, "Radar signal processing technology", IEICE, pp. 96-106 (1991)

  However, in the conventional radar device using the wavelet transform described above, the received signal is wavelet transformed, unnecessary components are removed on the wavelet axis, and then recombined to return to a signal on the time axis. Is compared with a predetermined threshold level to determine the presence or absence of a target. Therefore, re-synthesis processing after wavelet transform is essential, and there is a problem that the circuit configuration and the scale of signal processing increase. Further, in the conventional radar apparatus using the wavelet transform described above, the problem that it is difficult to detect the target signal when the input signal includes unnecessary wave components such as clutter has not been solved.

  The present invention has been made to solve the above-described problems, and even if an input signal includes an unwanted wave component, the target can be detected efficiently using wavelet transform, and the circuit configuration and An object of the present invention is to provide a target detection apparatus capable of reducing the scale of signal processing.

  In order to achieve the above object, a first invention is generated by an antenna that transmits and receives a beam, a wavelet transform circuit that generates a plurality of wavelet expansion coefficients by performing discrete wavelet transform on a signal from the antenna, and a wavelet transform circuit. When the expansion coefficient selection circuit for selecting one wavelet expansion coefficient to be used for detection of the target signal from the plurality of wavelet expansion coefficients and the wavelet expansion coefficient selected by the expansion coefficient selection circuit are larger than a predetermined threshold level A detector that outputs a detection signal indicating that the target signal has been detected, and a pulse repetition period or sampling period of the beam transmitted and received by the antenna so that the target signal is included in the wavelet expansion coefficient with few unnecessary signals, And there are few unnecessary signals, including target signals. Characterized by comprising a detection control circuit for controlling the expansion coefficient selection circuit as wavelet expansion coefficients are selected.

  In a second aspect based on the first aspect, the detection control circuit calculates an average value of each of a plurality of wavelet expansion coefficients from the wavelet transform circuit, and the target signal is included in the wavelet expansion coefficient having a small calculated average value. The expansion coefficient selection circuit is controlled such that the pulse repetition period or sampling period of the beam transmitted and received by the antenna is set, and the wavelet expansion coefficient including the target signal is selected with a small average value. .

  In a third aspect based on the first aspect, the detection control circuit calculates an average value of each of the plurality of wavelet expansion coefficients from the wavelet transform circuit, and the calculated average value is n (n is 2 or more). The pulse repetition period or sampling period of the beam transmitted / received at the antenna is sequentially set so that the target signal is included in the (integer) wavelet expansion coefficient, and n wavelet expansion coefficients including the target signal having a small average value are sequentially selected. The expansion coefficient selection circuit is controlled so that the detector has at least m (m is an integer of 2 or more and m ≦ n) or more among n wavelet expansion coefficients sequentially selected in the expansion coefficient selection circuit. A detection signal indicating that the target signal has been detected is output when the threshold level is greater than the threshold level.

  According to the first invention, when an unnecessary signal such as clutter is included in the received signal, the pulse repetition period of the beam transmitted and received by the antenna so that the target signal is included in the wavelet expansion coefficient with less unnecessary signal. Alternatively, since the sampling period is controlled, the influence of unnecessary signals can be reduced and the target detection capability can be improved.

  According to the second invention, when the received signal includes an unnecessary signal such as clutter and the wavelet expansion coefficient with a small number of unnecessary signals is unknown, it is not necessary that the average value of the wavelet expansion coefficient is small. Configured to control the pulse repetition period or sampling period of the beam transmitted and received at the antenna so that the target signal becomes the wavelet expansion coefficient, judging that the signal is small and the target signal is easy to detect Therefore, it is possible to reduce the influence of unnecessary signals and improve the target detection capability.

  According to the third invention, when the received signal includes an unnecessary signal such as clutter and the wavelet expansion coefficient with few unnecessary signals is unknown, a signal with a small average value of the wavelet expansion coefficient is unnecessary. It is determined that the target signal is a wavelet expansion coefficient with a small signal and easy to detect the target signal, and the pulse repetition period or sampling period of the beam transmitted and received at the antenna is controlled so that the target signal becomes the wavelet expansion coefficient When a discrete wavelet transform is performed with n pulse repetition periods or sampling periods, and when m or more are greater than a predetermined threshold level, a detection signal indicating that the target signal has been detected is output, so the width of the target signal varies Even in this case, the target detection performance can be ensured.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, a case where the target detection device according to the present invention is applied to a radar device for searching will be described. In the following embodiments, the same or corresponding components will be described with the same reference numerals.

  FIG. 1 is a block diagram illustrating the configuration of the target detection apparatus according to the first embodiment of the present invention. This target detection apparatus includes an antenna 10, a wavelet transform circuit 11, a development coefficient selection circuit 12, a CFAR circuit 13, a detector 14, and a detection control circuit 15.

  The antenna 10 transmits and receives beams at an interval instructed by a PRI control signal for controlling a pulse repetition period (hereinafter referred to as “PRI: Pulse Repetition Interval”) from the detection control circuit 15. A signal generated based on the beam (input data) received by the antenna 10 is sent to the wavelet transform circuit 11.

The wavelet transform circuit 11 performs a discrete wavelet transform on the signal transmitted from the antenna 10. Here, when a signal input to the wavelet transform circuit 11 is represented by a complex signal f0 (I + jQ), the signal f to be subjected to discrete wavelet transform is four types shown in the following equations (1) to (4). Can be considered.

here,
I: Real part Q: Imaginary part j: Imaginary unit The wavelet transform circuit 11 performs discrete wavelet transform on such a signal f to obtain a plurality of wavelet expansion coefficients wk. The discrete wavelet transform approximates an input signal (original waveform) as shown in FIG. 3A with a scaling coefficient and a wavelet expansion coefficient. The scaling coefficient has a plurality of levels 1 to J, and the degree of approximation differs depending on each level. The wavelet expansion coefficient corresponds to the difference between the levels of the scaling coefficient.

Such a discrete wavelet transform can be represented by a time-frequency filter. FIG. 2 is a diagram illustrating filter characteristics of the discrete wavelet transform. In order of level, the frequency domain transitions from wide to low. That is, it has a filter characteristic for a short time in the high band, and has a filter characteristic for a long time as it goes to the low band. This filter characteristic can be expressed by the following equations (5) to (10) as described in Non-Patent Document 1, for example.

here,
fj: j-level approximation function (j = 1 to J)
gj: j level expansion function sk: scaling expansion coefficient (k = 1 to K)
wk: Wavelet expansion coefficient φ: Scaling function ψ: Mother wavelet function pk: Sequence determined by the mother wavelet function *: Complex conjugate Here, w shown in Equation (9) is an approximate function and an actual waveform at level j And a wavelet expansion coefficient. FIG. 3 shows how the wavelet expansion coefficient is calculated. When this discrete wavelet transform is used, there is an advantage that a target signal representing a target can be detected with a small number of hits. The wavelet expansion coefficient obtained in the wavelet transform circuit 11 is sent to the expansion coefficient selection circuit 12.

  The expansion coefficient selection circuit 12 selects one wavelet expansion coefficient from a plurality of wavelet expansion coefficients W1 to WJ sent from the wavelet transform circuit 11 according to a selection control signal sent from the detection control circuit 15, The data is sent to the CFAR circuit 13.

  The CFAR circuit 13 generates a signal in which the false alarm probability is suppressed to a certain low level for the wavelet expansion coefficient sent from the expansion coefficient selection circuit 12 and sends the signal to the detector 14. Details of the CFAR processing performed in the CFAR circuit 13 are described in Non-Patent Document 2, for example.

  FIG. 4 is a block diagram showing a configuration of a linear CFAR circuit that performs normalization by arithmetic mean as an example of the CFAR circuit 13. The CFAR circuit 13 includes a delay circuit 51, an adder circuit 52, an averaging processing circuit 53, and a divider circuit 54.

  The delay circuit 51 delays the input signal xi and then sends it to the adder circuit 52 and the divider circuit 54. The adder circuit 52 adds the N pieces of data sent from the delay circuit 51 during a certain period, and sends it to the averaging processing circuit 53. The averaging processing circuit 53 calculates the average value of the N pieces of data sent from the adding circuit 52 and sends it to the dividing circuit 54. The division circuit 54 divides the data sent from the delay circuit 51 by the average value and outputs the result. The CFAR circuit 13 can also be realized by a logarithmic CFAR circuit that performs normalization with a geometric mean.

  The detector 14 compares the signal sent from the CFAR circuit 13 with a predetermined threshold level. If the signal sent from the CFAR circuit 13 is larger than the predetermined threshold level as a result of the comparison, the detector 14 detects that the target has been detected. A detection signal representing is output.

  The detection control circuit 15 determines the PRI so that the wavelet expansion coefficient Wc used for target detection is different from the wavelet expansion coefficient Wp including unnecessary signals such as clutter. Note that a sampling period in the range direction can be used instead of PRI, and the same applies to other embodiments described later. The PRI determined by the detection control circuit 15 is sent to the antenna 10 by the PRI control signal. Further, the detection control circuit 15 sends a selection control signal for selecting the wavelet expansion coefficient Wc used for target detection from the plurality of wavelet expansion coefficients to the expansion coefficient selection circuit 12.

  Next, the operation of the target detection apparatus according to Embodiment 1 of the present invention configured as described above will be described. First, the general operation will be described.

  In the discrete wavelet transform in the wavelet transform circuit 11 described above, if the input signal (original waveform) includes a non-stationary signal such as noise, the non-stationary signal is included in the wavelet expansion coefficient. Therefore, in order to remove noise from the input signal, the conventional radar apparatus shown in FIG. 12 is expected to decompose the input signal by the equations (5) to (10) and include noise among the wavelet expansion coefficients. The output signal from which noise and the like have been removed is obtained by recombining with the equations (5) to (10).

  On the other hand, in the target detection apparatus according to the present invention, focusing on the fact that the target signal to be detected is included in the wavelet expansion coefficient after decomposing the input signal, a predetermined signal is generated on the axis of the wavelet expansion coefficient. The target signal is detected by comparing with the threshold level. For this purpose, CFAR processing is performed on the axis of the wavelet expansion coefficient, and a signal exceeding a predetermined threshold level is set as a detection signal representing a target.

  In this case, as shown in FIG. 5, when the wavelet expansion coefficient including an unnecessary signal such as clutter is known, the wavelet expansion coefficient including the target signal is not matched with the wavelet expansion coefficient including the unnecessary signal. PRI is selected.

  Next, the detailed operation of the target detection apparatus according to the first embodiment of the present invention will be described with reference to the flowchart shown in FIG.

  When the search is started, the beam position is first set (step S11). The beam position is set to a predetermined position in the search area for the first time, and is set so that the beam direction sequentially moves in the search area after the second time.

Next, PRI setting and wavelet expansion coefficient setting are performed (step S12). The wavelet expansion coefficient Wc including the target signal can be determined from ^c that satisfies ns = ^2c , where ns is the width of the target signal included in the input signal. Similarly, the wavelet expansion coefficient Wp including the unnecessary signal can be determined from ^p satisfying ns = 2p, for example, where ns is the width of the unnecessary signal included in the input signal.

  Therefore, the detection control circuit 15 determines the PRI so that the wavelet expansion coefficient Wc is different from the wavelet expansion coefficient Wp including the unnecessary signal, and sets the PRI to the antenna 10 by the PRI control signal. The detection control circuit 15 sends a selection control signal for selecting the wavelet expansion coefficient Wc to the expansion coefficient selection circuit 12.

  Next, discrete wavelet (DWT) transformation is performed (step S13). That is, the wavelet transform circuit 11 performs discrete wavelet transform on the input signal to generate a wavelet expansion coefficient, and sends it to the expansion coefficient selection circuit 12. The expansion coefficient selection circuit 12 selects a wavelet expansion coefficient corresponding to the signal width of the target signal in accordance with the selection control signal from the detection control circuit 17 and sends it to the CFAR circuit 13.

  Next, CFAR processing is performed (step S14). That is, the CFAR circuit 13 performs CFAR processing on the wavelet expansion coefficient sent from the expansion coefficient selection circuit 12 and sends it to the detector 14. The detector 14 compares the signal sent from the CFAR circuit 13 with a predetermined threshold level, and outputs a detection signal if the signal sent from the CFAR circuit 13 is larger than the predetermined threshold level.

  Next, it is checked whether or not the search for the entire space has been completed (step S15). If it is determined in step S15 that the search of the entire space has not been completed, the sequence returns to step S11, the beam direction is changed to the next direction, and the above-described processing is repeated. On the other hand, if it is determined in step S15 that the search of the entire space has been completed, the beam direction is returned to the initial position of the search space (step S16). Thereafter, the sequence returns to step S11, and the above-described processing is repeated.

  The target detection apparatus according to the first embodiment described above is configured to detect the target when the wavelet expansion coefficient including the unnecessary signal is known. However, the target detection apparatus according to the second embodiment has few unnecessary signals. The target can be detected even if the wavelet expansion coefficient is unknown.

  FIG. 7 is a block diagram illustrating a configuration of the target detection apparatus according to the second embodiment of the present invention. In this target detection device, the detection control circuit 15 of the target detection device according to the first embodiment is replaced with another detection control circuit 16, and the wavelet expansion coefficient output from the wavelet transform circuit 11 is sent to the detection control circuit 16. It is configured as follows.

  The detection control circuit 16 accumulates the wavelet expansion coefficients sent from the wavelet transformation circuit 11, and calculates the average value of part or all of the accumulated wavelet expansion coefficients for each PRI. Then, as shown in FIG. 8, a wavelet expansion coefficient whose average value is equal to or lower than a predetermined threshold level is determined for target detection. This is because the average value of wavelet expansion coefficients that contain many unnecessary signals is small because unnecessary signals such as clutter have a low frequency, while the average value of wavelet expansion coefficients that contain few unnecessary signals is high because the frequency is high. Is to be used. The detection control circuit 16 sends a selection control signal for selecting the determined target detection wavelet expansion coefficient to the expansion coefficient selection circuit 12.

The wavelet expansion coefficient Wc including the target signal can be determined from ^c satisfying ns = ^2c , where ns is the width of the target signal included in the input signal. The PRI is determined so that the wavelet expansion coefficient Wc is different from the wavelet expansion coefficient Wp to be included, and is set to the antenna 10 by the PRI control signal.

  Next, the operation of the target detection apparatus according to Embodiment 2 of the present invention configured as described above will be described with reference to the flowchart shown in FIG. Note that steps that perform the same processing as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the description is simplified.

  When the search is started, first, a specific beam position is set (step S21). As the specific beam position, a beam position with many unnecessary signals such as clutter is used. Next, PRI is set (step S22). That is, the PRI is determined so as to have the wavelet expansion coefficient Wc determined by the width ns of the target signal, and is set in the antenna 10 by the PRI control signal.

  Next, wavelet transformation is performed (step S23). That is, the wavelet transform circuit 11 performs discrete wavelet transform on the input signal to generate a wavelet expansion coefficient and sends it to the detection control circuit 16. Next, the average value of the wavelet expansion coefficient is calculated (step S24). That is, the detection control circuit 16 calculates an average value of part or all of the time for each of the wavelet expansion coefficients sent from the wavelet transform circuit 11.

  Next, a wavelet expansion coefficient used for target detection is determined (step S25). That is, the detection control circuit 16 determines a wavelet expansion coefficient whose average value is equal to or lower than a predetermined threshold level for target detection. Next, the target detection PRI is determined (step S26). That is, the detection control circuit 16 determines the PRI so that the wavelet expansion coefficient Wc is different from the wavelet expansion coefficient Wp including the unnecessary signal.

  Thereafter, the same processing as that of the first embodiment (steps S11 to S16) shown in the flowchart of FIG. 6 is executed. That is, first, the beam position is set (step S11). Next, the setting of the PRI determined in step S26 and the setting for selecting the wavelet expansion coefficient determined in step S25 are performed (step S12). Next, discrete wavelet (DWT) transformation is performed (step S13). Next, CFAR processing is performed (step S14). Next, it is checked whether or not the search of the entire space has been completed (step S15). If it is determined that the search of the entire space has not been completed, the sequence returns to step S11 and the beam direction is changed to the next direction. Then, the process described above is repeated. On the other hand, if it is determined in step S15 that the search of the entire space has been completed, the beam direction is returned to the initial position of the search space (step S16). Thereafter, the sequence returns to step S11, and the above-described processing is repeated. The details of the processing executed in steps S11 to S16 are the same as those in the first embodiment.

  The target detection apparatus according to the second embodiment described above enables target detection when the width of the target signal is constant. However, the target detection apparatus according to the third embodiment has a variable target signal width. However, it is possible to detect the target.

  FIG. 10 is a block diagram illustrating the configuration of the target detection apparatus according to the third embodiment of the present invention. This target detection device is configured by replacing the detection control circuit 16 of the target detection device according to the second embodiment with another detection control circuit 17. Further, the function of the detector 14 is different from that of the target detection apparatus according to the second embodiment.

  The detection control circuit 17 accumulates the wavelet expansion coefficients sent from the wavelet transform circuit 11, and calculates an average value of part or all of the accumulated wavelet expansion coefficients for each PRI. Then, a wavelet expansion coefficient whose average value is equal to or less than a predetermined threshold level is determined for target detection. Then, the detection control circuit 16 sends a selection control signal for selecting the determined target detection wavelet expansion coefficient to the expansion coefficient selection circuit 12.

Further, since the wavelet expansion coefficient Wc including the target signal can be determined from ^c satisfying ns = ^2c , where ns is the width of the target signal included in the input signal, the detection control circuit 16 is generally known. The PRI is determined based on the width ns of the target signal so that the wavelet expansion coefficient Wc is different from the wavelet expansion coefficient Wp including the unnecessary signal, and n antennas including the preceding and succeeding PRIs are determined as antennas by the PRI control signal. Sequentially set to 10.

  The detector 14 compares signals sequentially sent from the CFAR circuit 13 by a wavelet transform performed by n (n is an integer of 2 or more) PRI with a predetermined threshold level, and accumulates the result of the comparison. . When the number of the comparison results among the n comparison results is greater than or equal to m (m is an integer of 2 or more and m ≦ n) indicating that the signal transmitted from the CFAR circuit 13 is greater than the predetermined threshold level. A detection signal indicating that the target has been detected is output.

  Next, the operation of the target detection apparatus according to the third embodiment of the present invention configured as described above will be described with reference to the flowchart shown in FIG. Note that steps that perform the same processing as in the second embodiment are denoted by the same reference numerals as in the second embodiment, and the description is simplified.

  When the search is started, first, a specific beam position is set (step S21). Next, PRI is set (step S22). Next, wavelet transformation is performed (step S23). Next, the average value of the wavelet expansion coefficient is calculated (step S24). Next, a wavelet expansion coefficient used for target detection is determined (step S25). Next, the target detection PRI is determined (step S26). In this case, the detection control circuit 16 determines n including PRIs before and after the PRI determined to have a wavelet expansion coefficient Wc different from the wavelet expansion coefficient Wp including the unnecessary signal, as the target detection PRI.

  Next, the beam position is set (step S11). Next, the setting of the PRI determined in step S26 and the setting for selecting the wavelet expansion coefficient determined in step S25 are performed (step S12). Next, discrete wavelet (DWT) transformation is performed (step S13). Next, CFAR processing is performed (step S14). That is, the CFAR circuit 13 performs CFAR processing on the wavelet expansion coefficient sent from the expansion coefficient selection circuit 12 and sends it to the detector 14. The detector 14 compares the signal sent from the CFAR circuit 13 with a predetermined threshold level and accumulates the comparison result.

  Next, it is checked whether or not the processing has been completed for n PRIs (step S41). If it is determined in step S41 that the process has not ended, the sequence returns to step S12, and the above-described processing is repeated. On the other hand, if it is determined in step S41 that the processing has been completed for n PRIs, m / n detection is performed (step S42). That is, the detection control circuit 17 has m results (m is an integer equal to or greater than 2) indicating that the signal sent from the CFAR circuit 13 is larger than a predetermined threshold level among the n comparison results stored. When m ≦ n), a detection signal indicating that the target has been detected is output.

  Next, it is checked whether or not the search of the entire space has been completed (step S15). If it is determined that the search of the entire space has not been completed, the sequence returns to step S11 and the beam direction is changed to the next direction. Then, the process described above is repeated. On the other hand, if it is determined in step S15 that the search of the entire space has been completed, the beam direction is returned to the initial position of the search space (step S16). Thereafter, the sequence returns to step S11, and the above-described processing is repeated. Refer to the second embodiment for details of the processes executed in steps S21 to S26, and refer to the first embodiment for details of the processes executed in steps S11 to S16.

  In the target detection apparatus according to the first to third embodiments described above, the target is detected by performing the CFAR processing on the wavelet expansion coefficient obtained by wavelet transforming the input data. For example, a fixed threshold is used. A method of detecting a target using a level, or a method of detecting a target by other methods can also be used.

  In the target detection apparatus according to the first to third embodiments, the target is detected by the CFAR process. However, for example, a method of comparing with a fixed threshold level or other detection methods can be used.

  In addition, in the target detection apparatuses according to the second and third embodiments, when calculating the average value of the wavelet expansion coefficients, if there is a margin for the search time, not only a specific beam position but also a plurality of beam positions are grouped. The beam can be directed to each group, and the average value of the wavelet expansion coefficients can be calculated.

  In the target detection apparatus according to the third embodiment, the wavelet expansion coefficient including the unnecessary signal is obtained by using the average value of the wavelet expansion coefficient. However, if the wavelet expansion coefficient having a low average value is generally known in advance. For example, the process for calculating the average value can be omitted.

  The target detection apparatus according to the present invention can be used for a radar apparatus or a reception apparatus.

It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 1 of this invention. It is a figure which shows the filter characteristic of discrete wavelet transform. It is a figure which shows a mode that a wavelet expansion coefficient is calculated in discrete wavelet transformation. FIG. 2 is a block diagram illustrating a configuration of a CFAR circuit illustrated in FIG. 1. It is a figure for demonstrating the wavelet expansion coefficient with few influences of the unnecessary signal used in the target detection apparatus which concerns on Example 1 of this invention. It is a flowchart for demonstrating the detailed operation | movement of the target detection apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 2 of this invention. It is a figure for demonstrating the wavelet expansion coefficient with little influence of the unnecessary signal used in the target detection apparatus which concerns on Example 2 of this invention. It is a flowchart for demonstrating operation | movement of the target detection apparatus which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the target detection apparatus which concerns on Example 3 of this invention. It is a flowchart for demonstrating operation | movement of the target detection apparatus which concerns on Example 3 of this invention. It is a figure for demonstrating the target detection apparatus using the conventional wavelet transform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna 11 Wavelet transformation circuit 12 Expansion coefficient selection circuit 13 CFAR circuit 14 Detector 15-17 Detection control circuit

Claims (3)

An antenna for transmitting and receiving beams;
A wavelet transform circuit for generating a plurality of wavelet expansion coefficients by performing discrete wavelet transform on the signal from the antenna;
An expansion coefficient selection circuit that selects one wavelet expansion coefficient used for detection of a target signal from among a plurality of wavelet expansion coefficients generated by the wavelet transform circuit;
A detector that outputs a detection signal indicating that a target signal has been detected when the wavelet expansion coefficient selected by the expansion coefficient selection circuit is greater than a predetermined threshold level;
The pulse repetition period or sampling period of the beam transmitted and received by the antenna is set so that the target signal is included in the wavelet expansion coefficient with few unnecessary signals, and the wavelet expansion coefficient including the target signal with few unnecessary signals is selected. A detection control circuit for controlling the expansion coefficient selection circuit,
A target detection apparatus comprising: The detection control circuit includes:
An average value of each of a plurality of wavelet expansion coefficients from the wavelet transform circuit is calculated, and a pulse repetition period or sampling of a beam transmitted and received in the antenna so that the target signal is included in the calculated wavelet expansion coefficient having a small average value 2. The target detection apparatus according to claim 1, wherein the expansion coefficient selection circuit is controlled so that a wavelet expansion coefficient that sets a period and has a small average value and includes a target signal is selected. The detection control circuit includes:
An average value of each of a plurality of wavelet expansion coefficients from the wavelet transform circuit is calculated, and the antenna is set such that the target signal is included in n wavelet expansion coefficients having a small average value (n is an integer of 2 or more). Sequentially setting the pulse repetition period or sampling period of the beam transmitted / received in and controlling the expansion coefficient selection circuit so that n wavelet expansion coefficients having a small average value and a target signal are sequentially selected;
The detector is
This indicates that the target signal is detected when m (m is an integer of 2 or more and m ≦ n) or more among n wavelet expansion coefficients sequentially selected in the expansion coefficient selection circuit is greater than a predetermined threshold level. The target detection apparatus according to claim 1, wherein a detection signal is output.

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