JPH0559387B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radar signal processing device that automatically detects a target of a pulse radar device.

(Prior Art) Radar received signals include unnecessary received signals (hereinafter referred to as clutter) in addition to the target signal. The intensity and amplitude distribution characteristics vary depending on the topography and weather conditions of the radar search space, so if automatic target detection is performed with a fixed threshold across the entire search space, these unnecessary received signals will cause the target signal to be distorted. Detection may become impossible or a received signal other than the target signal may be mistakenly detected as the target.

For this reason, in radar equipment that performs automatic target detection, the entire search area is divided into small areas (also called unit areas) determined by a predetermined distance range and coverage area.
In addition, it has a means for independently determining a threshold value and changing the threshold value according to the amplitude of the received signal to suppress erroneous target detection due to clutter and detect the target.

A typical example of this means is shown in FIG. In FIG. 2, a radar reception signal is detected and then input as a reception video 201 to a video selection circuit 202, a clutter suppression circuit 203, and an automatic clutter detection circuit 204.

In the clutter suppression circuit 203, MTI, LOG/
After suppressing clutter using CFAR or the like, the signal is sent to the video selection circuit 202. Automatic clutter detection circuit 2
04, the continuity of received signals exceeding a predetermined amplitude in the distance direction, azimuth direction, or both, or the frequency (number of times) of exceeding a predetermined amplitude for each predetermined small area is determined by a preset reference value. The video selection circuit 20 detects whether the input received signal is in the clutter area by comparing the clutter area signal with the clutter area signal.
Output to 2.

The video selection circuit 202 receives the clutter area signal, selects the processed video 205 that has undergone clutter suppression processing in the clutter area, and selects the normal video in other areas and outputs it as the selected video 206.

One of the selected videos 206 is sent to a threshold code update circuit 207. The threshold update circuit 207 determines the average level of the maximum value of the selected video 206 for each small region of the distance range ΔR and the azimuth range Δθ as shown in FIG. ) This is updated every predetermined radar scan.

As shown in FIG. 3b, the amplitude discrimination uses the maximum amplitude value of the selected video in the small area and the previous amplitude discrimination results sent from the memory 208 described below to determine the selected video 206 of each small area. N levels from T ₀ to T N-1 (hereinafter referred to as threshold code) whose maximum amplitude level is statistically set within the receiver dynamic range.
Determine which one corresponds to.

That is, in FIG. 3, if the amplitude discrimination result so far is at the level _T1 , the maximum amplitude of the selected video will be T at a certain frequency (for example, m scan among M scans, M>m, and M and m are both integers). When it exceeds ₁ , the amplitude discrimination result for the small region of interest is
It becomes T ₂ and is updated one step up.

Also, if the scan does not exceed T ₁ consecutively, it becomes T ₀ and is updated one step lower.

The threshold code thus updated for each small area is sent to the memory 208 again.

The memory 208 stores the latest threshold code for each small area for all search areas, and outputs the threshold code for a predetermined small area to the threshold code update circuit 207 in accordance with the timing of the selected video 206. do.

The threshold code output from the threshold code updating circuit 207 is also sent to the target detection level generation circuit 209, where it is converted into an actual threshold level (target detection level) corresponding to the threshold code. The signal is sent to the target detection circuit 210. This threshold level remains constant until the threshold code is updated. The target detection level is a value obtained by applying a predetermined bias to the level corresponding to the threshold code, and when the threshold code is T (dB), the target detection level is T (dB) + α (dB) ( α: constant value).

The target detection circuit 210 inputs the selected video 206 and the target detection level of the area corresponding thereto, and when the selected video 206 exceeds the target detection level, it detects this as a target detection signal 211 and outputs it.

In a normal radar system, position data corresponding to this target signal is extracted as target data, and this target data is used as input to perform track tracking processing by a computer.

(Problems to be Solved by the Invention) The conventional signal processing device described above divides the search space into small areas with a range width ΔR and an azimuth width Δθ, determines a threshold independently for each small area, and detects a target. However, since the threshold is determined only by controlling each small area, if the amplitude characteristics of clutter fluctuate, the number of clutter falls per scan over the entire search space (the number of detected targets) ) cannot be kept within a predetermined range.

In other words, in the conventional device, when the clutter is in a steady state under good weather, the parameters for updating the threshold and the target detection level are set so that the average value of the number of clutter falls per scan is equal to or less than a predetermined value. A bias value for determination is determined to prevent overflow of the computer input for track tracking processing connected to the signal processing device, but if the amplitude characteristics of clutter vary greatly from the steady state, the clutter per scan will be reduced. The toughalls number may significantly exceed the predetermined value mentioned above. In this case, since conventional signal processing devices do not have a function to control target detection based on the number of Clutter falses per scan, the number of Clutter false errors continues to be large and the computer input overflows. The problem is that it brings about

An object of the present invention is to calculate the average value of the number of target detections per scan from the number of target detections for each scan of a predetermined number of scans, and to If the preset upper limit value is exceeded by a preset number of scans, the threshold level for target detection is raised, and the preset lower limit value is not reached by a preset number of scans. In this case, by lowering the threshold level for target detection, even if the amplitude characteristics of clutter fluctuate, the number of targets detected over the entire search space (clutter false number) can be kept within a predetermined range, and the wake It is an object of the present invention to provide a radar signal processing device in which input to a tracking processing computer does not cause overflow.

(Means for Solving the Problems) The present invention has the following means configuration to achieve the above object. That is, the radar signal processing device of the present invention receives a normal video that is a video obtained by amplitude-detecting the received signal of a pulse radar device that emits a high-frequency pulse signal into space and receives its reflected signal, and calculates the amplitude value and its value. automatic clutter detection means for automatically detecting clutter from a received pattern and outputting a clutter gate signal indicating a clutter area; video selection means for selecting and outputting a normal video for a clutter area and selecting and outputting a video subjected to clutter suppression processing for a clutter area; By statistically processing the output of the video selection means for each unit area over the entire search area, a signal (called a threshold code) representing the maximum amplitude level of the output of the video selection means for each unit area is obtained.
an amplitude discrimination threshold code updating means for outputting the threshold code and updating the same in accordance with fluctuations in the output of the video selection means; receiving the threshold code and the target detection level control signal; target detection level generating means for outputting a threshold signal for target detection;
A target that receives an output signal of the video selection means and a threshold signal for target detection and outputs a target detection signal indicating that the target has been detected when the output signal of the video selection signal exceeds the threshold. detection means; clutter area detection target coefficient meter means for counting and outputting the number of target detection data in the clutter area for each scan of the radar in response to the output of the automatic clutter detection means and the output of the target detection means; Average target detection number calculation means for calculating and outputting the average value of the number of target detection data over a predetermined N scans (N is a positive integer); 1
If the average number of detected targets exceeds the first reference value by a predetermined number of n ₁ scans (n ₁ is an integer), a target detection level control signal is generated to raise the threshold for target detection. is output to the target detection level generating means, and if the average number of target detections does not exceed a predetermined second reference value by more than a predetermined _n2 scan ( _n2 is an integer), the target detection level is output to the target detection level generating means. target detection level control signal generation means for outputting a target detection level control signal for lowering the threshold value to the target detection level generation means;
A radar signal processing device characterized by having the following features.

(Function) Hereinafter, the function of the radar signal processing device of the present invention having the above-described configuration will be explained.

A pulse radar device emits a high-frequency pulse signal into space and receives reflected signals that are reflected back from various radio wave reflectors. A signal called a normal video signal is obtained by amplitude detection of this received signal. The automatic clutter detection means receives this normal video signal, automatically detects clutter from its vibration value and its reception pattern, and outputs a clutter gate signal indicating that the signal is in a clutter area.

In the present invention, this clutter gate signal is used for two purposes. Part 1 is used as a signal for video signal selection by the video selection means described below, and Part 2 is used as a signal for limiting the counting of the number of detected targets within the clutter region by means for counting the number of detected targets in the crack area, described later. used.

The video selection circuit receives a normal video signal and MTI (Moving Target Indication) as its input.
and LOG/CFAR (Logarithmic/Constant False
A clutter gate signal from an automatic clutter detection means selects and outputs a clutter suppressed video in a clutter area, and outputs a normal video when it is not in a clutter area. Select and output.

The output signal of the video selection means is sent to the amplitude discrimination threshold code updating means and the target detection means.

The amplitude discrimination threshold code updating means statistically processes the video signal from the video selection means for each unit area of a predetermined azimuth range and distance range in the entire search area of the radar, and updates the video signal for each unit area. A signal representing the maximum amplitude level of the output of the selection means (this is called a threshold code) is output while being updated in accordance with fluctuations in the output of the video selection means. This threshold code is sent to the target detection level generating means.

The target detection level generation means receives the threshold code and a target detection level control signal from the target detection level control signal generation means described later, and generates a threshold signal for target detection in accordance with the threshold code. occurs. This threshold signal is sent to target detection means.

A video signal is inputted to the target detection means from the video selection means, and when this video signal exceeds a threshold value, it is determined that a target has been detected and a target detection signal is output. This target detection signal is outputted as an output of the radar signal processing device to a computer for tracking processing, and is also added to means for counting the number of targets detected within the clutter area.

The clutter area detection target number counting means counts the number of target detection data within the clutter area in one radar scan from the target detection signal using the clutter gate signal from the automatic clutter detection means.

This count signal is sent to the average target detection number calculation means. The average target detection number calculation means calculates the average value of the number of target detection data per scan over a predetermined number of scans (for example, N scans), and sends this calculation result to the target detection level control signal generation means. Send. In addition to this average value signal, an upper limit value signal and a lower limit value signal predetermined for the average value are added to the target detection level control signal generating means.

The target detection level control signal generating means receives each of these signals and determines whether the average value per scan (average number of target detections) exceeds the upper limit value or more than a predetermined number of scans (for example, n ₁ times). In this case, a target detection level control signal is sent to the target detection level generating means to raise the threshold for target detection, and the number of scans in which the average number of target detections does not exceed the lower limit is determined in advance (for example,
n _times ) or more, a target detection level control signal that lowers the threshold for target detection is sent to the target detection level generating means, and the average number of target detections exceeds the lower limit value and is within the upper limit value. At this time, a target detection level control signal is sent to the target detection level generating means to leave the threshold value for target detection as it is.

As described above, in the signal processing device of the present invention, the means for counting the number of detected targets in the clutter region, the means for calculating the average number of detected targets, the means for generating the target detection level control signal, and the means for generating the target detection level form a negative feedback loop system. A threshold value is applied to the target detection means so that the average number of target detections within the clutter region in the target detection signal output from the target detection means is within a predetermined range determined by the upper and lower limits. Since the signal is controlled, even if the amplitude characteristics of the clutter change, the number of targets detected within the clutter region, that is, the number of clutter falls, remains within a predetermined range, and the computer input for track tracking processing in the conventional technology is Problems such as overflow are eliminated.

〔Example〕

Embodiments of the radar signal processing device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the radar signal processing device of the present invention.

The automatic clutter detection circuit 1 includes a comparator 2, a shift register 3, a counter 4, a comparator 5, a clutter area determination circuit 6, a memory 7, and a video selection signal generation circuit 8.

The normal video 9 is input to the comparator 2, and is compared with a predetermined level threshold 10 which is input separately, and when the threshold is equal to or higher than the threshold 10, the logic is "1", and when it is less than the threshold, the logic is "0", and so on. The signal is quantized and output to the shift register 3. The shift register 3 is an M-stage shift register that stores quantized data of a predetermined number M unit distances of the output of the comparator 2.

The data in each of the M stages of the shift register 3 is sent to the counter 4.

The counter 4 receives the data from the shift register 3, counts the number of "1"s or "0"s in the data in each stage of the shift register 3, and sends the counted value to the comparator 5.

The comparator 5 compares this counted value with a predetermined threshold 11 that is input separately, and when it is large, it sends a logic "1", and when it is small, it sends a logic "0" to the clutter area determination circuit 6. do.

The clutter area determination circuit 6 divides the entire search space into small areas (unit areas) with a unit distance ΔR and a unit azimuth width Δθ, and even once in the portion of the normal video corresponding to the small area, the output of the comparator 5 is determined to be a logic "1", that small area is designated as a clutter area, and a logic "1" signal is output to the memory 7 for that small area. The memory 7 records the output data of the clutter area determination circuit 6 for all unit areas of the unit distance ΔR and unit azimuth width Δθ, and sends the recorded data to the video selection signal generation circuit 8.

The video selection signal generation circuit 8 receives the data from the memory 7 and generates a video selection signal 13 which is a clutter gate signal for selecting an MTI-CFAR video for a small area determined to be a clutter area.
Output. This video selection signal 13 is sent to a video selection circuit 15 and a clutter area detection target number counting circuit 14.

The normal video 9 and the MTI-CFAR video 12, which is a clutter suppression processed video, are input to the video selection circuit 15. According to the video selection signal 13, the MTI-CFAR video 12 is selected and output in the clutter area, and the clutter is suppressed. If it is not the area, normal video 9 is selected and output.
The selected video 23, which is the output signal of the video selection circuit 15, is sent to the amplitude discrimination threshold code update circuit 16 and the target detection circuit 17.

Amplitude discrimination threshold hold code update circuit 1
6 includes a maximum amplitude detection circuit 18, an amplitude discrimination threshold generation circuit 19, a comparator 20, a threshold code update circuit 21, and a memory 2.
It is composed of 2.

The selected video 23 is the maximum amplitude detection circuit 1 in the amplitude discrimination threshold code update circuit 16.
Added to 8. The maximum amplitude detection circuit 18 detects the maximum amplitude value for each unit area from the selected video 23 and sends it to the comparator 20.

The memory 22 stores a threshold code for each unit area over the entire search area, and transmits the threshold code of the corresponding unit area to the amplitude discrimination threshold generation circuit 19 in accordance with the timing of the selected video 23. The threshold code is sent to the threshold code update circuit 21.

The amplitude discrimination threshold generation circuit 19 converts the received threshold code into a threshold for amplitude discrimination and sends it to the comparator 20.

Comparator 20 compares the maximum amplitude value from maximum amplitude detection circuit 18 with the threshold from amplitude discrimination threshold generation circuit 19 and sends the result to threshold code update circuit 21 .

The threshold code change circuit 21 accumulates the comparison results from the comparator 20 over a predetermined number of scans, and stores the results and the memory 2
2, the threshold code is updated and output at predetermined time intervals according to predetermined logic.

The updated threshold code is sent to the memory 22 to rewrite the threshold code in the memory 22, and is also sent to the target detection level generation circuit 24.

The target detection level generation circuit 24 receives a target detection level control signal from a target detection level control signal generation circuit 26 (described later) in addition to the threshold code, and generates a plurality of predetermined thresholds for each threshold hold code. One of the target detection threshold levels is selected by the target detection level control signal and output to the target detection circuit 17 as the target detection threshold level for the selected video 23 of each unit area.

The target detection circuit 17 determines that the target has been detected and outputs a target detection signal when the selected video 23 from the video selection circuit 15 exceeds the target detection threshold level. This target detection signal is output as an output of the radar signal processing device to a computer for tracking processing, and is also applied to a circuit 14 for counting the number of targets detected in the clutter area.

In the cluster area detection target number counting circuit 14,
The target detection signal and the video selection signal 13 are logically summed, the target detection signal outside the clutter area is removed, and then the number of target detection signals is counted, and this count signal is sent to the average target detection number calculation circuit 25.

The counting interval is one scan of the radar, and this is done by resetting the counting operation every time a north pulse 27, which indicates the timing when the radar antenna direction becomes magnetic north or true north, arrives.

The average target detection number calculation circuit 25 calculates an average value (average target detection number) from this count signal for each predetermined number of scans.

Now, assuming that the output of the i-th scanned clutter area detection target number counting circuit 14 is Ni, the average target detection number calculation circuit 25 calculates the average number of detections N using the following equation (1).

Here, l is the number of scans for calculating the average value, and p is an arbitrary integer.

The average target detection number thus calculated is sent to the target detection level control signal generation circuit 26.

The target detection level control signal generation circuit 26 generates a target detection threshold when the number of scans in which the average number of target detections exceeds the average detection number upper limit value 28 inputted separately exceeds a predetermined number _n1 times. A target detection level control signal (logic level "0") to increase the hold level is sent to the target detection level generation circuit 24, and a scan is performed in advance so that the average target detection number does not exceed the average detection number lower limit value 29 input separately. When the predetermined number of times _n2 or more is reached, a target detection level control signal (logic level "2") that lowers the target detection threshold level is sent to the target detection level generation circuit 24,
When the average target detection number exceeds the average detection number lower limit value 29 and is within the average detection number upper limit value, the target detection level control signal (logic level "1") is set to keep the target detection threshold level as it is. It is sent to the detection level generation circuit 24.

The target detection level generation circuit 24 has a predetermined value n for one threshold code.
It has a function of generating different types of target detection threshold levels, and one of them is selected by the target detection level control signal.

That is, if the level corresponding to a certain threshold code is T (dB) in S/N conversion, the target detection threshold level is T + α
(dB), T+2α(dB),...n of T+n・α(dB)
Streets are possible.

When the signal processing device shown in this embodiment is reset, it is first set to T+nα/2 (when n is an even number) or T+
(n±1)α/2 (when n is an odd number) is output as the target detection threshold level.

After that, when the target detection level control signal is at logic level "0", a threshold level that is one step higher than the previous threshold level is selected, and when the target detection level control signal is at logic level "1", the threshold level is selected. Select the threshold level as before, and when the target detection level control signal is at logic level "2", select the threshold level one step lower than before, and output from the target detection level generation circuit 24. shall be.

In this way, the number of target detections within the clutter area, ie, the number of clutter falls, falls within a predetermined range.

In addition, the values mentioned as "predetermined values" in the above explanation are determined under the environment in which the radar is installed, and differ depending on the environment, so they are meaningless. It is not something that is determined.

Furthermore, although this embodiment has been described for the case of a two-dimensional radar, the small area in the automatic clutter detection circuit 1 and the small area in the amplitude discrimination threshold code updating circuit 16 are three-dimensional (unit distance, unit azimuth, unit elevation angle). By doing so, it can also be applied as a signal processing device for three-dimensional radar.

(Effects of the Invention) The radar signal processing device of the present invention has the configuration and operation described above, and detects targets such that the number of detected targets in the clutter region (i.e., the number of clutter falls) falls within a predetermined value range. Since the threshold level for target detection is controlled and set, even if the amplitude characteristics of the clutter fluctuate, the bias value for generating the threshold level for target detection will follow up and down. This has the advantage that it is possible to prevent overflow of computer inputs that are concatenated in increasing numbers.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the configuration of a conventional radar signal processing device, and FIG. 3 is an explanatory diagram of the operation of the conventional radar signal processing device. . 1... automatic clutter detection circuit, 2... comparator,
3...Shift register, 4...Counter, 5...Comparator, 6...Clutter area determination circuit, 7...Memory, 8...Video selection signal generation circuit, 9...Normal video, 10, 11... ...Threshold, 12...MTI-CFAR video, 13...Video selection signal, 14...Clutter area detection target number counting circuit, 15...Video selection circuit, 16...
Amplification discrimination threshold code update circuit, 1
7...Target detection circuit, 18...Maximum amplitude detection circuit, 19...Threshold generation circuit for amplitude discrimination, 20...Comparator, 21...Threshold code update circuit, 22...Memory, 23... …
Selection video, 24...Target detection level generation circuit,
25...Average target detection number calculation circuit, 26...Target detection level control signal generation circuit, 27...North pulse, 28...Average detection number upper limit value, 29...Average detection number lower limit value.

Claims (1)

[Claims] 1. Receiving a normal video which is a video obtained by amplitude detection of a received signal of a pulse radar device that radiates a high frequency pulse signal into space and receives the reflected signal, clutter is detected from the amplitude value and the reception pattern. automatic clutter detection means for automatically detecting a clutter gate signal indicating a clutter area; A video selection means for selecting and outputting a normal video and selecting and outputting a video subjected to clutter suppression processing for a clutter area; A signal representing the maximum amplitude level of the video selection means output for each unit area (referred to as a threshold code) is output by statistical processing of the output of the video selection means for each unit area over the area, and the video selection means an amplitude discrimination threshold code updating means for updating the amplitude discrimination threshold code in accordance with fluctuations in the output; a threshold signal for target detection for the threshold code in response to the threshold code and a target detection level control signal; target detection level generating means for outputting; upon receiving the output signal of the video selection means and a threshold signal for target detection, the target is detected when the output signal of the video selection means exceeds the threshold; target detection means for outputting a target detection signal indicating that;
clutter region detection target number counting means for receiving the output of the automatic clutter detection means and the output of the target detection means, and counting and outputting the number of target detection data in the clutter region for each scan of the radar; an average target detection number calculation means for calculating and outputting an average value of the number of target detection data over scans (N is a positive integer); and a first reference value predetermined as the output of the average target detection number calculation means. The average number of target detections is predetermined compared to n ₁
When the scan ( _n1 is an integer) or more exceeds the first reference value, a target detection level control signal for raising the threshold for target detection is output to the target detection level generating means, and the average target detection A second reference value whose number is predetermined is predetermined.
target detection level control signal generating means for outputting a target detection level control signal for lowering a threshold for target detection to the target detection level generating means if the target detection level does not exceed _n2 scans ( _n2 is an integer); A radar signal processing device comprising: