JP2014174068A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which, upon detecting and tracking by an M-PRF(Medium-Pulse Repetition Frequency) in a pulsed Doppler radar, target tracking may be unstable due to an influence of a cloud in the vicinity of the target.SOLUTION: In a selection of a noise area upon performing a CFAR (Constant False Alarm Rate) process, when respective frequencies of highest signal intensity in top two noise areas having high average signal intensity coincide with each other, the top two noise areas are configured to be excluded from a selection object. Thereby, an influence of a cloud can be removed, and it becomes possible to continue to always perform correct and stable tracking.

Description

The present invention relates to a radar apparatus. More specifically, the present invention relates to a radar apparatus that performs M-PRF (Medium-Pulse Repetition Frequency) tracking signal processing.

Conventionally, an aircraft-mounted pulse Doppler radar has performed CFAR (Constant False Alarm Rate) processing in M-PRF tracking signal processing (see, for example, Non-Patent Document 1 and Patent Document 1). .

JP 2012-159343 A

Guy Morris Linda Harkness, "Airborne Pulsed Doppler Radar Second Edition", ARTECH HOUSE, Inc, Chapter 6

CFAR processing calculates the S / N ratio based on the difference in signal strength between the detection target position in the received signal and the noise region set around it, and determines whether the target signal exists at the detection target position. It is processing to do.

However, when there is a reflected signal from the cloud in the vicinity of the target, the S / N ratio of the target signal deteriorates due to the reflected signal from the cloud entering the noise area in the CFAR processing, and detection and tracking become unstable. There is a problem of becoming.
As disclosed in Patent Document 1, it is considered to determine weather clutter based on the magnitude of a reflected signal, or to remove weather clutter by simply adjusting a threshold value, but M-PRF in a pulse Doppler radar mounted on an aircraft. In processing, further improvement measures have been demanded in target detection accuracy.

The CFAR processing in M-PRF detection and tracking is performed on an FR map (Frequency-Range) depicted on a two-dimensional axis represented by time (distance) and Doppler frequency (velocity). In general CFAR processing, the ratio of the intensity of a signal present in a detection target cell and the intensity of a signal present in a surrounding noise region is defined as an S / N ratio, and the signal to be tracked in the detection target cell is detected. The presence or absence was judged.

X-band electromagnetic waves widely used in aircraft-mounted pulse Doppler radars have the property of being reflected by clouds as well as artificial objects such as aircraft. For this reason, when a cloud exists around the target aircraft and is captured in the beam of the own radar, a reflected signal from the cloud may be reflected in the FR map.

When a cloud exists in the vicinity of the target aircraft, a cloud signal is generated in the vicinity of the target signal on the time axis in the FR map.
Although the moving speed is significantly different between the target aircraft and the cloud, the cloud signal may also appear on the frequency axis on the FR map depending on the direction of travel and the frequency axis folding processing in the FR map. It may occur near the target signal.

In this way, when a cloud signal appears in the vicinity of the target signal and further enters the noise region in the CFAR process, the signal strength in the noise region increases, so the S / N of the target signal that is the target of tracking relatively. The ratio will decrease.
As a result, there have been problems such as failure in target detection, tracking failure, tracking transfer to a cloud signal, and the like.

The present invention has been made to solve the problem, and by using the difference in characteristics between the target signal and the cloud signal, the two are separated, and the influence of the reflected signal from the cloud is removed. The purpose is to realize stable detection and tracking even in a situation where clouds exist in the vicinity of the target aircraft.

A radar apparatus according to the present invention includes a receiver connected to an antenna, and a signal processing unit that detects a target signal from radar reception signals received by the receiver, wherein the signal processing unit includes: An FR signal generation unit that creates an FR map in which the signal strength of the radar reception signal is plotted on two-dimensional coordinates represented by distance data and frequency data, and an area to be subjected to CFAR processing on the FR map The S / N ratio is calculated using the average signal strength in the selected region and the signal strength of the selected target candidate signal, and the target candidate signal is calculated when the S / N ratio is equal to or greater than a predetermined threshold value. Includes a target determination unit that determines that the signal is a target signal, and the target determination unit includes signals having a predetermined intensity or higher at the same frequency in two regions of the target regions of the CFAR processing. The case was the two regions to be excluded from the target area of the CFAR processing.

According to the radar apparatus of the present invention, the target signal is accurately detected even in a situation where the S / N ratio of the target signal to be tracked relatively decreases due to the cloud signal or the like being reflected in the vicinity of the target signal. It is possible to detect well and perform stable detection and stable tracking of the target.

It is the figure which showed the structure of the radar apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows operation | movement of the signal processing part in Embodiment 1 of this invention. It is explanatory drawing for demonstrating the target detection by a general signal processing method. It is explanatory drawing for demonstrating generation | occurrence | production of a cloud signal. It is explanatory drawing for demonstrating the target detection by the signal processing part (FIG. 2) in Embodiment 1 of this invention. It is a flowchart for demonstrating the target detection by the signal processing part (FIG. 2) in Embodiment 1 of this invention.

Embodiment 1 FIG.
A radar apparatus and a signal flow according to the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention, and shows a configuration of a device that performs a range calculation process from reception of a radar wave in the radar apparatus. In FIG. 1, the radar apparatus includes an antenna 1, an excitation receiver 2, and a signal processor 3. The signal processor 3 further includes a signal processing unit 4 and a data processing unit 5.
In FIG. 1, the antenna 1 receives a received signal, and the received signal processed by the excitation receiver 2 is sent to the signal processor 3. The signal processing unit 4 performs fast Fourier transform, CFAR processing, and peak detection, and acquires Doppler frequency data.
The obtained Doppler frequency data is sent to the data processing unit 5.

The CFAR process performed by the signal processing unit 4 will be described. FIG. 2 is a block diagram showing the operation of the signal processing unit 4.
The signal processing unit 4 has a function of detecting a target signal from the reception signals received from the excitation receiver 2 and outputting the target signal to the data processing unit 5.
The signal processing unit 4 includes an FR signal generation unit 101, a detection signal intensity calculation unit 102, a detection signal data storage unit 103, a detection target instruction unit 104, a noise level calculation unit 105, a noise data storage unit 106, a noise region selection unit 107, a target The determination unit 108 is configured.

The FR signal generation unit 101 generates data constituting an FR map for the radar reception signal input from the excitation receiver 2. The distance data is obtained from the signal reception time, and the frequency data is calculated by performing fast Fourier transform and amplitude detection for each distance.
The FR signal generation unit 101 creates an FR map by plotting the signal intensity on two-dimensional coordinates represented by distance data (time axis) and frequency data (frequency axis), and uses the created FR map as a detection signal intensity. It outputs to the calculation part 102 and the noise level calculation part 105.

The detection signal strength calculation unit 102 obtains signal strengths for all cells in the target detection processing target range on the created FR map, assigns cell addresses, and stores them in the detection signal data storage unit 103. .
Note that the target detection processing target range is given by an external operation or operation mode, and varies depending on the difference between search and tracking, but this difference does not affect the effect of the invention.

The detection signal data storage unit 103 stores cell signal strength data input from the detection signal strength calculation unit 102. Further, the signal strength data is output to the target determination unit 108 in accordance with the instruction of the detection target instruction unit 104.

The detection target instruction unit 104 stores in advance a range to be subjected to CFAR processing on the FR map.
The detection target instruction unit 104 sets a detection target cell within this range, and sends the address of the cell to the detection signal data storage unit 103. Further, the address of the detection target cell is sent to the noise region selection unit 107, and noise data corresponding to the detection target cell is selected. These processes are sequentially performed on all cells in the target range.
The target range of the CFAR process is given by an external operation or an operation mode, and varies depending on the difference between search and tracking, but this difference does not affect the effect of the invention.

The noise level calculation unit 105 sets a noise region based on each cell for all cells existing in the processing target range on the obtained FR map, and calculates an average signal intensity in the noise region.
Furthermore, in the present invention, not only the average signal strength but also the frequency of the cell having the highest signal strength in the noise area (noise region) is calculated.
A combination of the average signal strength and the frequency of the cell having the highest signal strength is set as one noise data, and a cell address is assigned and stored in the noise data storage unit 106.
Note that the noise region is a region having a certain size on the FR map, and its shape is stored in the noise level calculation unit 105 in advance. The shape of the noise region needs to have a certain length in the frequency axis direction, but other features do not affect the effect of the invention.

The noise data storage unit 106 stores the noise data input from the noise level calculation unit 105. Further, noise data is output to the noise region selection unit 107 in accordance with an instruction from the noise region selection unit 107.

The noise region selection unit 107 acquires noise data corresponding to the address instructed from the detection target instruction unit 104 from the noise data storage unit 106 and outputs the noise data to the target determination unit 108.

In general, in the CFAR processing, in order to recognize a portion having a higher intensity than the surrounding as a signal, a plurality of regions existing around the detection target cell are set as a noise region on the basis of the detection target cell. The relative position between the detection target cell and the noise region to be selected is stored in the noise region selection unit 107 in advance.
FIG. 3 is an explanatory diagram for explaining target detection by a general signal processing method. For example, as shown in FIG. 3A, the noise region selection unit 107 has a frequency direction and a range direction of the detection target cell 109. In both cases, the noise data of the four noise regions 110 to 113 that are symmetrical is acquired from the noise data storage unit 106. Here, the number of noise regions does not affect the effect of the present invention, and a plurality of noise regions having different time axes may be set for one frequency.

FIG. 3B shows an outline of normal signal processing. In general, the noise data 115 in the noise region having the highest average signal strength is selected from the noise data 114 to 117 at these four locations, and the average signal strength is used as the noise in calculating the S / N ratio of the signal detection cell. Use as a value.
In the example of FIG. 3B, since the average signal strength of the noise data 115 is sufficiently smaller than the signal strength of the target signal 118, the target signal 118 is exceeded when the calculated S / N ratio exceeds the determination threshold value. Successful detection.

According to this method, when a cloud signal having a larger signal strength than the standard noise enters the noise region, and the average signal strength of the noise region is increased, the S / N ratio of the signal detection cell is relative. And the normal CFAR processing result cannot be obtained.
Therefore, in the present embodiment, cloud signal determination is added as a noise region selection method in the present invention.

Usually, clouds that affect target tracking are much larger than aircraft.
FIG. 4 is an explanatory diagram for explaining the generation of cloud signals. As shown in FIG. 4, the radar beam emitted from the own aircraft is continuously transmitted from one end of the cloud to the other end of the cloud. Causes reflection. Since the distance information in the real space appears on the time axis on the FR map, the cloud signal 119 is reflected as a signal extending long in the time axis direction on the FR map. Further, the entire cloud has a substantially constant velocity, and takes a constant value on the frequency axis on the FR map.

An outline of cloud signal determination is shown in FIG. FIG. 5 is a diagram for explaining target detection by the signal processing unit 4 and shows that a cloud signal 119 exists in the vicinity of the target signal 118.
As described above, the cloud signal 119 has a shape extending long in the time axis direction at the same frequency.
Here, of the noise regions 110 to 113 that are evenly arranged around the signal detection target cell, the noise region 112 and the noise region 113 are affected by the cloud signal.
For this reason, the signal processing unit 4 in the present embodiment uses the noise region 110 and the noise region 111 existing on the opposite side of the cloud signal on the frequency axis to calculate the S / N ratio for signal detection, thereby Remove the effects of.

In order to remove the noise region affected by the cloud signal from the process, it is necessary to determine whether the cloud signal exists. In order to determine that the cloud signal is reflected in the noise region, the present embodiment uses a shape that extends long in the time axis direction at the same frequency peculiar to the cloud signal. The noise data stored in the noise data storage unit 106 includes the frequency of the cell having the highest signal strength in addition to the average signal strength in the noise region. Since the cloud signal extending long in the time axis direction at the same frequency is reflected in both the noise region 112 and the noise region 113, the noise data 116 of the noise region 112 and the noise data 117 of the noise region 113 have the highest signal intensity. High cell frequencies will match.

When the target determination unit 108 selects a noise region to be used for S / N ratio calculation from the four noise regions, a condition using this feature is added. In general noise region selection, a noise region having the highest average signal strength is selected. In the present invention, the top two noise regions (noise region 112 and noise region 113) having the highest average signal strength are selected first. Regarding the noise data (noise data 117 and noise data 118) included in these noise regions, if the frequencies of the cells having the highest signal intensity match, it is determined that the cloud signal is reflected in both noise regions. Are excluded from the noise region selection target.

The target determination unit 108 selects the larger one of the remaining two noise regions (the noise region 110 and the noise region 111), and uses the average signal strength as a noise value in calculating the S / N ratio of the detection target signal. Used as If the calculated S / N ratio satisfies a preset threshold value and the peak detection is successful, the signal of the detection target cell is output as a target signal to the data processing unit 5.

As described above, it is possible to perform signal detection processing in a state where the influence of the signal shape is removed by using the feature of the signal shape of the cloud signal extending in the time axis direction.

Next, the operation of the signal processing unit 4 will be described.
FIG. 6 is a flowchart showing the operation of the signal processing unit 4 of FIG. In FIG. 2, the signal processing unit 4 generates an FR map using the radar reception signal input from the excitation receiver 2, and detects the detected signal intensity and noise data for all cells in the target range on the FR map. Each is calculated and stored as a data series (step S101).

The signal processing unit 4 selects one of the cells existing within the CFAR target range in the FR map as a detection target cell (step S102). Further, the signal intensity of the detection target cell is stored as a signal value at the time of calculating the S / N ratio (step S103).

On the FR map, the signal processing unit 4 selects the top two noise regions having the highest average signal strength from the noise regions existing at positions defined in advance with reference to the detection target cell (step S104). For the noise data of these noise regions, the frequency of the cell having the highest signal strength is compared (step S105). If the two match as a result of the comparison, these two noise regions are excluded from selection targets, and the determination based on the average signal intensity is performed on the remaining two noise regions (step S106).

If the frequency of the cell with the highest signal strength does not match for the top two noise regions with the highest average signal strength from the noise data, the noise region with the highest average signal strength is used for CFAR processing as before. Used (step S107).

The signal processing unit 4 calculates the S / N ratio using the signal intensity of the detection target cell as a signal value and the average signal intensity of the selected noise region as a noise value. If the value of the S / N ratio exceeds a preset CFAR threshold value and the peak detection is successful, it is determined as a target signal and the target signal data is output to the data processing unit 5 (steps S108 and S109). If it is not determined to be the target signal, nothing is output to the data processing unit 5 (step S110). Thereafter, the same operation is repeated for all cells existing in the CFAR target range in the FR map.

As described above, according to this embodiment, in the M-PRF detection and tracking by the airborne radar, it is possible to exclude the influence of clouds and always perform stable detection and tracking.

Note that the above embodiment is merely an example, and if it is a pulse Doppler radar that detects and tracks a target using frequency information and range (time) information, it is not only an aircraft but also a ground-mounted type. Needless to say, the present invention can be similarly applied to a radar or the like.

DESCRIPTION OF SYMBOLS 1 Antenna, 2 Excitation receiver, 3 Signal processor, 4 Signal processing part, 5 Data processing part, 101 FR signal generation part, 102 Detection signal strength calculation part, 103 Detection signal data storage part, 104 Detection object instruction | indication part, 105 Noise level calculation unit 106 Noise data storage unit 107 Noise region selection unit 108 Target determination unit 109 Detection target cell 110-113 Noise region 114-117 Noise data 118 Target signal 119 Cloud signal

Claims (4)

A radar device comprising a receiver connected to an antenna, and a signal processing unit for detecting a target signal from radar received signals received by the receiver,
The signal processing unit generates an FR map in which the signal intensity of the radar reception signal is plotted on two-dimensional coordinates represented by distance data and frequency data, and a CFAR (Constant False) on the FR map. (Alarm Rate: constant false alarm probability) A region to be processed is selected, an S / N ratio is calculated using the average signal strength in the selected region and the signal strength of the selected target candidate signal, and the S / N A target determination unit that determines that the target candidate signal is a target signal when the ratio is equal to or greater than a predetermined threshold;
The target determining unit excludes the two areas from the target area for the CFAR process when signals having a predetermined intensity or higher exist at the same frequency in the two areas among the target areas for the CFAR process. A characteristic radar device. A radar device comprising a receiver connected to an antenna, and a signal processing unit for detecting a target signal from radar received signals received by the receiver,
The signal processing unit
Create an FR map in which the signal strength of the radar reception signal is plotted on two-dimensional coordinates represented by distance data and frequency data, and output the FR map to a detection signal strength calculation unit and a noise level calculation unit And
In the FR map, a detection signal strength calculation unit that obtains signal strengths in a plurality of cells to which addresses are assigned in a target detection target range;
A detection signal data storage unit that stores data of signal strength for each cell and outputs data of signal strength in a cell indicated by a detection target instruction unit to a target determination unit;
In the FR map, a noise region based on the cell is preset for each cell in the target range, and an average signal strength in the noise region and a frequency of a cell having the highest signal strength in the noise region are calculated. A noise level calculator,
For each noise region, a noise data storage unit that stores, as noise data, a combination of the average signal strength in the noise region and the frequency of the cell having the highest signal strength;
A noise region selection unit that obtains noise data for each noise region from the noise data storage unit and outputs the noise data to the target determination unit;
An S / N ratio is calculated using the signal strength input from the detection signal data storage unit and the highest average signal strength among the average signal strengths for each of the noise regions input from the noise region selection unit, A target determination unit that determines that a signal in the cell is a target signal when the S / N ratio is equal to or greater than a predetermined threshold;
The target determination unit selects the top two noise regions having the highest average signal strength among the average signal strengths for each of the noise regions input from the noise region selection unit, and has the highest signal strength in the selected noise region. When the frequencies of the high cells match, the S / N ratio is calculated using the highest average signal strength among the average signal strengths of other noise regions excluding the upper two noise regions. Radar device. The radar apparatus according to claim 2, wherein the noise region has a certain length in the frequency axis direction in two-dimensional coordinates represented by a distance and a frequency. 4. The radar apparatus according to claim 3, wherein the noise region is set in advance at four or more locations around the position of the target signal in two-dimensional coordinates represented by distance and frequency.

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