JP5425370B2 - Radar apparatus signal processing method and radar apparatus - Google Patents

Description

  The present invention relates to a radar apparatus, and particularly to a radar apparatus that performs target detection processing using CFAR (Constant False Alarm Ratio) processing or the like.

  As a radar apparatus according to the prior art, there is a document disclosing a target detection processing technique called a side lobe blanker (for example, Non-Patent Document 1).

  This technique called a sidelobe blanker is divided into a main antenna (hereinafter referred to as “Main antenna” or simply “Main”) and a guard antenna (hereinafter referred to as “Guard antenna”) having a smaller gain and a wider beam width than the Main antenna. Or simply referred to as “Guard” and received by the Guard antenna with the amplitude value of the signal received by the Main antenna (hereinafter referred to as “Main amplitude”) and the magnitude of noise (hereinafter referred to as “Main noise”). An index value obtained by combining a signal amplitude value (hereinafter referred to as “Guard amplitude”) and a noise value (hereinafter referred to as “Guard noise”) is determined based on a predetermined plurality of thresholds, and the detected target is Determine if it is a true target, clutter or jamming Is a target detection process technology characterized and.

  Note that this sidelobe blanker has been attracting attention as a target detection processing technique that can reduce the probability that clutter and jamming waves are detected as targets, that is, the occurrence probability of erroneous targets.

Guy V. Morris "AIRBORNE PULSE DOPPLER RADER" Georgia Tech Research Institute. Arttech House.

  However, in the related art shown in Non-Patent Document 1 and the like, when the target is located at a long distance, or when the target is a low RCS, that is, when the target is a small amplitude target, the amplitude output by the Guard antenna is not generated. There is a problem that the threshold determination by a plurality of thresholds does not sufficiently function because of being buried in noise, and a false target is detected as a target that is not a true target.

  The present invention has been made in view of the above, and provides a signal processing method for a radar apparatus and a radar apparatus that can suppress the occurrence probability of an erroneous target that erroneously detects a target that is not a true target. For the purpose.

In order to solve the above-described problems and achieve the object, a signal processing method of a radar apparatus according to the present invention is a narrow processing for irradiating a detection target with a transmission pulse and processing a signal reflected from the detection target. A main antenna that forms a beam antenna pattern; and a guard antenna that forms an antenna pattern having a beam width wider than the narrow beam antenna pattern, and each amplitude value due to a reflected signal and noise received via the main antenna; In a signal processing method of a radar apparatus for detecting a true target based on a reflected signal received via the guard antenna and each amplitude value due to noise, the amplitude value (main amplitude of the reflected signal received via the main antenna) ) And the amplitude value of noise received through the main antenna (main noise) A first comparison and determination step for comparing the value to be determined with a predetermined first threshold, and a second ratio determined as a ratio between the main amplitude and the amplitude value (guard amplitude) of the reflected signal received via the guard antenna. A second comparison determination step for comparing the determination target value with a predetermined second threshold, and a third target value determined as a ratio between the guard amplitude and the amplitude value of the noise received via the guard antenna (guard noise). And a third comparison determination step for comparing the determination value with a predetermined third threshold value, and when it is determined that the comparison determination result by the first comparison determination step exceeds the predetermined first threshold value , the comparison determination result by the second comparison determination step without exceeding the predetermined second threshold value, and compares the determination result by the third comparison determination step does not exceed a predetermined third threshold value The case, characterized in that it suspends to determine the sense target as a true target.

According to the signal processing method of the radar apparatus according to the present invention, when the comparison determination result in the first comparison determination step exceeds the predetermined first threshold, the comparison determination result in the second comparison determination step is the predetermined first. When the comparison determination result by the third comparison determination step does not exceed the predetermined third threshold without exceeding the threshold of 2, the determination of the detection target as a true target is suspended. Therefore, there is an effect that it is possible to suppress the occurrence probability of an erroneous target that is erroneously detected as a target that is not a true target.

  Hereinafter, a radar apparatus and a signal processing method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by embodiment shown below.

[Embodiment]
(Configuration of radar device)
First, the configuration of the radar apparatus according to the embodiment of the present invention will be described. FIG. 1 is a block diagram showing a configuration of a radar apparatus according to an embodiment of the present invention. The radar apparatus shown in the figure shows a standard search and tracking radar configuration, and includes a transmitter 101, an antenna 102, a transmission / reception switch 103, a receiver 104, and a signal processing device 109. In addition, the signal processing device 109 is configured to include each component of an A / D converter 105, a frequency analyzer 106, an amplitude detector 107, and a target detector 108 therein.

(Operation of radar equipment)
Next, the operation of the radar apparatus shown in FIG. 1 will be described. In the figure, the transmission pulse generated by the transmitter 101 is radiated from the antenna 102 to the detection target as a radio wave via the transmission / reception switch 103. The radio wave reflected by the detection target is received again by the antenna 102 as a signal of two patterns of Main / Guard (described later) (see FIG. 4), and is input to the receiver 104 via the transmission / reception switch 103. The input signal input to the receiver 104 is amplified and phase detected by the receiver 104, converted to a digital video signal by the A / D converter 105, and input to the frequency analyzer 106. The converted signal input to the frequency analyzer 106 is subjected to FFT processing in the frequency analyzer 106 and converted into a signal on the frequency axis, and then the predetermined amplitude data (by Main / Guard) is output from the amplitude detector 107. Two patterns of amplitude output (Main amplitude, Guard amplitude) are generated and input to the target detector 108. In the target detector 108, target detection processing called CFAR processing is performed by using each amplitude output based on the input main amplitude and guard amplitude, and the detection result is output as target information.

(Configuration and operation of target detector)
Next, the configuration and operation of the target detector 108 in the radar apparatus shown in FIG. 1 will be described with reference to FIGS. Here, FIG. 2 is a diagram showing a detailed configuration of the target detector 108 shown in FIG. 1. Here, the CFAR processing (more specifically, GOCFAR (Greatest Of CFAR) processing) performed by the target detector 108 is shown. The flow is shown as an example. FIG. 3 is a flowchart showing a processing flow in the target detector 108. In FIG. 2, each of the main amplitude signal and the guard amplitude signal to be input is an amplitude detector after each received signal of Main / Guard is converted into a signal on the frequency axis by FFT processing of the frequency analyzer 106. 107 is converted into amplitude values of Main and Guard.

  First, the configuration of the target detector 108 will be described. In FIG. 2, the target detector 108 includes two processing systems: a processing system for processing the Main amplitude signal and a processing system for processing the Guard amplitude signal. The processing system for processing the main amplitude signal includes a main amplitude output attention cell 201, reference cells 202 and 203 provided as moving windows for the main amplitude output attention cell 201, and N reference cells 202 and 203 (N is a natural number). ) Are input to the average amplitude output calculation units 204 and 205, and the Main side average amplitude output comparison operation unit 206 to which the outputs of the average amplitude output calculation units 204 and 205 are input. Similarly, the processing system for processing the Guard amplitude signal includes N guard cells 207 and 209 provided as a moving window for the Guard amplitude output attention cell 207, and the Guard amplitude output attention cell 207, and N reference cells 208 and 209 ( The average amplitude output calculation units 210 and 211 to which outputs of N are natural numbers are input, and the Guard side average amplitude output comparison calculation unit 212 to which the outputs of the average amplitude output calculation units 210 and 211 are input are configured. In addition, a target determination unit 213 and a target determination threshold value 214 that holds a predetermined threshold value are configured subsequent to the target detector 108. Note that the target determination unit 213 sets the target based on the inputted outputs of the main-side average amplitude output comparison calculation unit 206 and the guard-side average amplitude output comparison calculation unit 212 and a predetermined threshold held by the target determination threshold 214. Is output as a target signal.

  Next, the operation of the target detector 108 will be described. In FIG. 2, the amplitude value written in the main amplitude output target cell 201 is output to the target determination unit 213 as the main amplitude. On the other hand, each processing unit of the average amplitude output calculation units 204 and 205 outputs N amplitude values written in the reference cells 202 and 203 corresponding to the main amplitude output target cell 201 with respect to the input main amplitude signal. Calculate the average value. The calculation result is output to the Main side average amplitude output comparison calculation unit 206. The main-side average amplitude output comparison calculation unit 206 selects the larger one of the calculation results of the average amplitude output calculation units 204 and 205, and outputs the selected value as the main noise to the target determination unit 213.

  Similar processing is performed on the Guard amplitude signal. That is, the amplitude value written in the guard amplitude output attention cell 207 is output to the target determination unit 213 as the guard amplitude. On the other hand, each of the processing units of the average amplitude output calculation units 210 and 211 outputs N amplitude values written in the reference cells 208 and 209 corresponding to the Guard amplitude output target cell 207 with respect to the input Guard amplitude signal. Calculate the average value. The calculation result is output to the Guard side average amplitude output comparison calculation unit 212. The Guard-side average amplitude output comparison calculation unit 212 selects the larger value among the calculation results of the average amplitude output calculation units 210 and 211, and outputs the selected value to the target determination unit 213 as Guard noise.

The target determination unit 213 determines whether or not a target exists according to the processing flow (see FIG. 3) to be described later (hereinafter, based on the following four threshold values held by the input signal and the target determination threshold value 214 (hereinafter referred to as “target determination”). (Referred to as “target determination process”), and a signal determined as a target is output as a target signal.
Threshold value 1: Ms / Mn threshold value Threshold value 2: Ms / Gs threshold value Threshold value 3: Gs / Gn threshold value Threshold value 4: Gn / Ms threshold value Here, the meanings of the symbols in the above equation are as follows.
Ms: Main amplitude Mn: Main noise Gs: Guard amplitude Gn: Guard noise

(Details of the target judgment process)
Next, details of the above-described target determination process will be described with reference to FIG. In the processing flow shown in FIG. 3, the target determination unit 213 performs threshold determination processing based on a combination of four amplitude values of Main amplitude and Guard amplitude and Main noise and Guard noise in the target cell.

  First, it is determined whether the Main amplitude / Main noise (ratio of Main noise to Main amplitude, hereinafter the same) in the target cell exceeds a threshold value 1 that is a preset first threshold value (step S301). ). If the main amplitude / main noise does not exceed the threshold value 1 (No in step S301), it is determined that there is no target because nothing is hit. On the other hand, when the main amplitude / main noise exceeds the threshold value 1 (step S301, Yes), it is determined that a target, clutter, interference wave, or the like has hit.

  Next, in a state where the main amplitude / main noise exceeds the threshold value 1, it is determined whether the main amplitude / guard amplitude exceeds the threshold value 2 that is the second threshold value set in advance (step S302). . If the Main amplitude / Guard amplitude exceeds the threshold 2 (Yes in step S302), it is determined that the hit is the target. On the other hand, if the main amplitude / guard amplitude does not exceed the threshold 2 (No in step S302), whether the guard amplitude / guard noise does not exceed the threshold 3 that is the third threshold set in advance. A determination is made (step S303).

  Here, if the Guard amplitude / Guard noise exceeds the threshold 3 (No at Step S303), it is determined that the clutter or the interference wave has hit. On the other hand, when the Guard amplitude / Guard noise does not exceed the threshold value 3 (Yes in step S303), it is further determined whether the Guard noise / Main noise exceeds a threshold value 4 that is a preset fourth threshold value. Is performed (step S304).

Here, when the Guard noise / Main noise is equal to or exceeds the threshold value 4 (No in step S304), it is determined that the clutter or the interference wave has hit. On the other hand, when the Guard noise / Main noise is smaller than the threshold value 4 (step S304, Yes), it is determined that the hit is the target.

  The above processing flow can be summarized as follows. That is, when the value of the main amplitude / main noise exceeds the threshold value 1 in the target cell, it is determined that a target, clutter, interference wave, or the like is hit. On the other hand, if the threshold value 1 is not exceeded, it is determined that nothing is hit. On the other hand, if the value of Main amplitude / Main noise exceeds the threshold value 1 and the Main amplitude / Guard amplitude does not exceed the threshold value 2, the target hits when the following two conditions are satisfied at the same time: Judge. One is that the guard amplitude / guard noise does not exceed the preset threshold value 3, and the other is that the guard noise / main noise exceeds the preset threshold value 4. If these two conditions are not satisfied at the same time, it is determined that the hit is a clutter or an interference wave, and it is determined that the target has not been hit. These processing flows can be expressed by mathematical expressions.

なお、上式における、記号の意味は、以下のとおりである。
Ｓ_M：Ｍａｉｎ振幅
Ｎ_M：Ｍａｉｎノイズ
Ｓ_G：Ｇｕａｒｄ振幅
Ｎ_G：Ｇｕａｒｄノイズ
Ｋ₁：閾値１
Ｋ₂：閾値２
Ｋ₃：閾値３
Ｋ₄：閾値４

The meanings of symbols in the above formula are as follows.
S _M : Main amplitude N _M : Main noise S _G : Guard amplitude N _G : Guard noise K ₁ : Threshold 1
K ₂ : threshold 2
K ₃ : threshold 3
K ₄ : threshold 4

  By the way, as described above, when the target is located at a long distance or when the target detects a small-amplitude target such as a low RCS, a false target is detected as a target that is not a true target. He raised the problem that it might end up. Therefore, as an example for explaining this problem, an operation when the antenna pattern as shown in FIG. 4 is present and a target as shown in FIG. 4 exists will be explained.

  In FIG. 4, the antenna 401 includes a main antenna and a guard antenna, and an antenna pattern generated by the antenna 401 includes an antenna pattern (main pattern) 402 by a main antenna and an antenna pattern (guard pattern) by a guard antenna. The antenna pattern shown in FIG.

  Here, a case where the target 404 shown in FIG. 4 is not a small amplitude target, that is, a target such as a long distance / low RCS (hereinafter referred to as “non-small amplitude target”) will be considered.

  FIG. 5 is a diagram showing the amplitude and noise characteristics of Main and Guard with respect to a non-small amplitude target. The left side shows the Main side signal characteristics, and the right side shows the Guard side signal characteristics. ing.

  In the graph on the left side of FIG. 5, the value of the main amplitude 502 in the target cell 501 sandwiched between two wavy lines is sufficiently larger than the value of the main noise 503. Further, the value of the Main amplitude 502 in the attention cell 501 is sufficiently larger than the value of the Guard amplitude 504 in the attention cell 501 in the graph on the right side of FIG. The target existing on the target cell can be hit.

  Next, consider a case where the target 404 is a small amplitude target such as a long distance / low RCS.

  FIG. 6 is a diagram showing the amplitude and noise characteristics of Main and Guard with respect to a small amplitude target. The left side shows the Main side signal characteristics, and the right side shows the Guard side signal characteristics. Yes.

  In each graph of FIG. 6, the value of the main amplitude 602 in the target cell 601 sandwiched between two wavy lines is sufficiently larger than the value of the main noise 603, and it is determined that something has hit. However, since the target 404 is a small amplitude target, the ratio of the Main amplitude 602 and the Guard amplitude 604 in the target cell of the target cell 601 is not sufficiently large, and the value of the Guard amplitude 604 in the target cell is the value of the Guard noise 605. The threshold condition for detection (corresponding to the thresholds 2 and 3 in the flow of FIG. 3) cannot be satisfied. In this case, in the cell of interest 601, the hit with the main amplitude does not hit with the guard because the target is a small amplitude target, or due to the spread of clutter or, for example, side lobe direction ECM (Electric Counter Measurements) signal. It cannot be judged whether the target is falsely detected. In the conventional method shown in Non-Patent Document 1 and the like, if the Guard amplitude / Guard noise falls below a predetermined threshold value (threshold value 3 in the case of the flow in FIG. 3), it is determined that the target is hit. The detection rate is not lowered.

  As described above, in the target detection method in the conventional method, the hit in the target cell may be erroneously detected as the target even though the clutter or the sidelobe direction ECM signal spreads. That is, the conventional method has a problem in that when a small amplitude target is detected, a target that is not a true target is erroneously detected as a target.

  The above event is caused by the fact that the Guard amplitude output is buried in noise when the target is a small amplitude target because the Guard amplitude output is lower than the Main amplitude output.

  Next, in order to explain the effect when the above-described target detection method according to the present invention is used, the antenna pattern as shown in FIG. 7 is provided and the target and the interference signal source as shown in FIG. The operation will be described as an example.

FIG. 7 shows an unnecessary signal 705 such as a clutter or ECM signal coming from the side lobe direction in addition to the Main / Guard antenna patterns and targets shown in FIG. In the following description, it is assumed that the target 704 is a small amplitude target such as a long distance / low RCS.

  FIG. 8 is a diagram showing the amplitude and noise characteristics of Main and Guard when an unnecessary signal is incident. The signal characteristics of the Main side are shown on the left side of the figure, and the signal characteristics of the Guard side are shown on the right side. Each is shown.

In each graph of FIG. 8, the value of the main amplitude 802 in the target cell 801 is sufficiently larger than the value of the main noise 803 and it is determined that something hits, but the main amplitude 802 in the target cell of the target cell 801 is determined. And the Guard amplitude 804 is not sufficiently large, and the Guard amplitude 804 in the target cell is not sufficiently higher than the value of the Guard noise 805, so whether the target is Hit at the time of the process of step S303 in FIG. The determination of whether or not is pending. In the conventional method, both the target 704 and the unnecessary signal 705 have been detected as targets at this point.

On the other hand, in the radar apparatus according to the present embodiment, the ratio of the Guard noise 805 and the Main noise 803 exceeds a predetermined threshold value (corresponding to the threshold value 4 in the flow of FIG. 3) as shown in the process of step S304 in FIG. By determining whether or not, the small amplitude target 704 and the unnecessary signal 705 can be separated. In other words, the small amplitude target 704 can be hit as the target, and the clutter, the side lobe direction ECM signal, etc. can be distinguished as not the target.

  As is clear from the comparison between the graphs of FIGS. 6 and 8, the above-described processing is not much different in the difference between the levels of the guard noise and the main noise in the small amplitude target, whereas the unnecessary signal This is due to the finding that the level of Guard noise increases in the presence.

  As described above, according to the present embodiment, the means for determining the cause of the decrease in the Guard signal level is incorporated in the target Hit condition in the sidelobe blanker when performing the CFAR process on the amplitude output. Therefore, compared with the conventional method, it is possible to more accurately distinguish between a target and an unnecessary signal, and it is possible to reduce target misdetection.

Further, according to the present embodiment, when a first determination value determined as a ratio between the main amplitude and the main noise is compared with the threshold value 1 and it is determined that the comparison result exceeds the threshold value 1, the main value is determined. If second determined value determined as the ratio between the amplitude and the Guard amplitude without exceeding the threshold value 2, and the third determination target value determined as the ratio of the Guard amplitude and Guard noise does not exceed the threshold value 3, Since the determination of the detection target as a true target is suspended, it is possible to suppress the probability of erroneous detection of a target that is not a true target.

Further, according to the present embodiment, for the detection target for which the target determination is suspended, the determination value determined as the ratio of the Guard noise and the Main noise is compared with the threshold value 4, and the determination value is the threshold value 4. If it is smaller than the threshold, the suspended detection object is determined as a true target, so that accurate target detection information can be provided.

  In the above embodiment, the antenna system has been described as having two antennas, a Main antenna and a Guard antenna, but two physically different antennas are not necessarily present. For example, an array antenna may be configured, and a narrow beam antenna pattern serving as a main pattern and a wide beam antenna pattern serving as a guard pattern may be formed by the array antenna.

  As described above, the radar apparatus according to the present invention is useful for a radar apparatus that performs target detection processing using CFAR processing or the like.

It is a block diagram which shows the structure of the radar apparatus concerning embodiment of this invention. It is a figure which shows the detailed structure of the target detector shown in FIG. It is a flowchart which shows the processing flow in a target detector. It is a figure which shows an example of each antenna pattern of Main / Guard, and the target of a detection target. It is a figure shown about the amplitude and noise characteristic of Main and Guard with respect to a non-small amplitude target. It is a figure shown about the amplitude and noise characteristic of Main and Guard with respect to a small amplitude target. FIG. 5 is a diagram in which unnecessary signals such as clutter or ECM signals coming from the side lobe direction are added to FIG. 4. It is a figure shown about the amplitude and the noise characteristic of Main and Guard when an unnecessary signal injects.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Transmitter 102 Antenna 103 Transmission / reception switch 104 Receiver 105 A / D converter 106 Frequency analyzer 107 Amplitude detector 108 Target detector 109 Signal processing device 201,207 Amplitude output attention cell 202,203,208,209 Reference cell 204, 205, 210, 211 Average amplitude output calculation unit 206 Main side average amplitude output comparison calculation unit 212 Guard side average amplitude output comparison calculation unit 213 Target determination unit 214 Target determination threshold

Claims (4)

A main antenna that forms a narrow beam antenna pattern for irradiating a detection target with a transmission pulse and processes a signal reflected from the detection target, and an antenna pattern having a wider beam width than the narrow beam antenna pattern And detecting a true target based on each amplitude value due to the reflected signal and noise received via the main antenna and each amplitude value due to the reflected signal and noise received via the guard antenna. In the signal processing method of the radar device,
A first determined value defined as a ratio between the amplitude value (main amplitude) of the reflected signal received via the main antenna and the amplitude value (main noise) of noise received via the main antenna is a predetermined first value. A first comparison determination step for comparing with a threshold value of
A second comparison and determination step of comparing a second determination value defined as a ratio between the main amplitude and the amplitude value of the reflected signal received via the guard antenna (guard amplitude) with a predetermined second threshold;
A third comparison and determination step of comparing a third determination value determined as a ratio between the guard amplitude and the amplitude value of the noise received via the guard antenna (guard noise) with a predetermined third threshold;
Including
When it is determined that the comparison determination result in the first comparison determination step exceeds the predetermined first threshold, the comparison determination result in the second comparison determination step exceeds the predetermined second threshold. And a radar apparatus that suspends the determination of the detection target as a true target when the comparison determination result of the third comparison determination step does not exceed the predetermined third threshold value. Signal processing method. A fourth determination value, which is determined as a ratio between the guard noise and the main noise, is compared with a predetermined fourth threshold value for a detection target whose target determination is suspended in the third comparison determination step. The comparison judgment step of
The signal of the radar apparatus according to claim 1, wherein the detection target is determined as a true target when a comparison determination result in the fourth comparison determination step is smaller than the predetermined fourth threshold value. Processing method. A main pulse for forming a narrow beam antenna pattern for irradiating a detection pulse with a transmission pulse and processing a signal reflected from the detection target, and an antenna pattern having a beam width wider than the narrow beam antenna pattern An antenna unit having a guard antenna;
A transmitter for supplying the transmission pulse to the antenna unit;
A receiving unit that converts an analog signal received by the antenna unit into a digital signal and outputs the digital signal;
A signal processing unit that performs predetermined processing on the digital signal output from the receiving unit to determine whether the detection target is a true target; and
In a radar apparatus equipped with
The signal processing unit
A first determined value defined as a ratio of an amplitude value (main amplitude) of a reflected signal received via the main antenna and an amplitude value (main noise) of noise received via the main antenna is a predetermined first value. When it is determined that the first determination value exceeds the predetermined first threshold value compared with a threshold value, the main amplitude and the amplitude value of the reflected signal received via the guard antenna (guard amplitude) A second determined value determined as a ratio to the second threshold value and a third threshold value determined as a ratio between the guard amplitude and the amplitude value of the noise received via the guard antenna (guard noise). A target determiner for comparing the determination value with a predetermined third threshold;
The target determiner is
When the second determination value does not exceed the predetermined second threshold and the third determination value does not exceed the predetermined third threshold, the detection target is determined as a true target. A radar apparatus characterized by holding. The target determiner is
For a detection target for which the target determination is suspended, a fourth determination value determined as a ratio of the guard noise and the main noise is compared with a predetermined fourth threshold value, and the fourth determination value is determined to be the predetermined predetermined value. 4. The radar apparatus according to claim 3, wherein when the threshold value is smaller than 4, the detection target for which the target determination is suspended is determined as a true target.

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