JPS62148873A - Radar equipment - Google Patents

Abstract

PURPOSE:To manage with only one automatic target detection processing system and to reduce the scale of hardware greatly by putting signals of plural systems after MDF processing and CFAR processing into a signal of one system while selecting one of the systems for every range bin by a selector, and then detecting a target. CONSTITUTION:A received video signal is inputted to an A/D converter 200 from an input terminal 100 and applied to Doppler filters 301-30N which have mutually different passing frequency bands and cover the entire Doppler frequency band by N channels in parallel, so that clutter signals are separated to individual Doppler filters respectively. Various clutter signals are divided by a mean value level through LOG/CFARs 311-31N and compressed and automatic gain control is performed AGLs 321-32N according to a clutter removal level; and maximum values are selected by the video selector 400 and put together into a signal of one system. The composite signal is supplied to an automatic target detection processor 500 for one channel to perform target detection processing, and the resulting signal is outputted from an output terminal 80.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a multi-doppler filter (Multi Doppler filter).
The present invention relates to a radar device including an unnecessary signal suppressing means including a p-ler filter (referred to as MDF) and an automatic target detecting means.

(Prior art) Target signals from aircraft, ships, vehicles, etc. are detected, and ground clutter (power reflected from the ground surface or ground structures such as mountains, forests, fields, buildings, etc.), sea surface clutter, and weather clutter ( In recent years, radars have been using MDF% and LOG/CFAR (Cons
An unnecessary signal suppressing means is employed that combines the following processes: tant Fa, Ise Alarm R-ate) processing.

This is based on the following principle.

That is, each target and each unwanted signal reflector has a unique relative velocity with respect to the radar, and as a result, each rake received signal from these reflectors has a unique Doppler frequency component.

Therefore, by constructing an MDF consisting of a plurality of top filters having mutually different passing frequency bands, it becomes possible to separate these reflected signals by utilizing the difference in Doppler frequency.

The target signal and clutter signal separated into separate Doppler filters are average-divided by LOG/CFAR processing prepared for each Doppler filter.

In general, clutter signals have a spatially uniform spread because individual reflection points that contribute to reflection exist in a sufficiently wide area compared to the radar resolution unit area determined by the radar beam width and pulse width. On the other hand, the target signal has the property that the physical size of the target object is usually equal to or smaller than the laser resolution unit area.
It has the characteristics of a so-called point target.

As a result, the clutter signal is sufficiently suppressed by the LOG/CFAR processing, whereas the target signal, which exists only in pulses in the distance direction, is basically not affected by the LOG/CFAR processing.

In particular, if the statistical properties of the amplitude of the clutter signal follow a Rayle distribution (it is known that most weather clutter and some sea surface clutter follow a Rayle distribution), then L
It has been theoretically shown that OG/CFAR processing can suppress the signal to the same level as the receiver noise.

In this way, LOG/C for each MDF and each Doppler filter
It is possible to separate the target signal and the clutter signal by FAR processing and suppress only the clutter signal.

The mission of the radar is to automatically detect only the target signal and notify the operator (radar monitor) by displaying a symbol.At the same time, it also shows the operator the radar radio environment status, such as the presence or absence of jamming waves or the presence of weather cracks. Accordingly, the radar video is displayed so that the operator can judge whether there is a target or not.

In order to automatically detect targets in a radar that performs MDF processing, it has conventionally been necessary to perform target detection processing for each Doppler filter.

This is due to the following reasons. That is, as described above, each type of clutter signal has its own Doppler frequency, and the statistical properties of the amplitude of the clutter signal differ depending on the object contributing to the reflection.

In cases where the object is originally a collection of homogeneous reflection points, such as a rain cloud, it is often described by the Lehree distribution, and conversely, in cases where it is an collection of reflection points that are not homogeneous, such as a ground clutter, it is described by the Lehrey distribution. is the Weibull distribution
distribution) and lognormal distribution (Log-
Normal distribution). In this way, the S-flux distribution characteristics of the clutter signal vary depending on the type of clutter, the physical properties of the reflecting object, etc., so the amplitude distribution characteristics after MDF processing and LOG/CFAR processing also vary widely. .

In particular, in areas where ground clutter exists, the Doppler frequency will remain in the Doppler filter around O, and there will be many residuals, and in areas where moving clutter such as weather cracks exists, the corresponding There will be residual noise in the Doppler filter around the Doppler frequency, and the amplitude distribution characteristics of the signal after LOG/CFAR processing will be clearly different from a Doppler filter in which only receiver noise exists.

On the other hand, in order to automatically detect a target, it is necessary to adapt to the amplitude distribution characteristics of various clutter remaining signals after clutter suppression processing, and to suppress the probability of erroneously detecting a clutter remaining signal as a target signal to a predetermined value or less. From 9 onwards, it is essential to automatically control the threshold level of
Conventionally, the signal amplitude distribution characteristics differed for each Doppler filter channel depending on the presence or absence of clutter and the type of clutter, and since the presence or absence and type of clutter changed depending on the area, automatic targets were set independently for each Doppler filter channel. It is equipped with a detection processing means.

(Problems to be Solved by the Invention) However, the conventional system in which an automatic target detection processing means is provided for each Doppler filter channel has the following drawbacks. The first drawback is that each Doppler filter channel is quantized by setting a threshold adapted to the clutter remaining level, and after target detection processing is performed using a binary signal of l or 0, correlation between each Doppler filter channel is required. Since it is a method that processes and ultimately determines the target, it is optimally processed by sufficiently applying clutter suppression processing, including target signal fluctuations and lucky information, and interpolating missing radar images peculiar to MDF processing. In the case where there is no processed video and automatic detection becomes inappropriate due to a defect in the automatic target detection processing system or the occurrence of obstruction/interference, it is not possible to provide the operator with images suitable for visual judgment. be.

The second drawback is that it is necessary to provide target detection processing systems equal to the number of Doppler filter channels, which increases the hardware scale.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a radar device with excellent operability and economy that can provide not only the symbol display as a result of automatic target detection but also the above-mentioned optimally processed video. There is a particular thing.

(Means for Solving the Problems) The present invention has the following means configuration to achieve the above object. That is, the radar device of the present invention is a radar device equipped with a multi-Doppler filter as a moving target identification means, and generally includes N (an integer greater than 1) Doppler filters; each connected to the output end of each Doppler filter. N CFAR processing means for converting and suppressing signals having the same amplitude distribution characteristics as receiver noise by automatically adapting to the amplitude distribution characteristics of the signal such as clutter and receiver noise; a selector connected to the output end of the processing means and composing N signals into one signal by selecting the output signal of any one CFAR processing means for each distance direction processing unit of the radar; an automatic target detection means connected to the output terminal; connected to the output terminal of the selector to interpolate the Doppler filter output signal once every M (≧N) transmitted pulses to obtain a signal for each transmitted pulse; A video playback means for playing back; and a D/A converter connected to the video playback means for generating analog processed video.

(Function) Hereinafter, the present invention having the above means will be explained in detail.
In the present invention, as in the prior art, CFAR processing means corresponding to the number of MDFs and their number of systems (for example, N) are connected to each system of the MDF. However, the CFA4 processing means in the present invention is a CFAR processing means that automatically adapts to the amplitude distribution characteristics of signals such as clutter and receiver noise, converts them into signals having the same amplitude distribution characteristics as the receiver noise, and suppresses them. is used, so the remaining state of clutter is the same between each system.

Therefore, even if one of the N systems is selected for each distance direction processing unit (range bin) and one system of signals is generated, the same remaining signal will be obtained. A target can be detected by a target detection device.

Therefore, the outputs of each of the N systems of CFAR processing means are sent to a selector, and by selecting and extracting one of the outputs of the N systems of CFAR processing means for each range bin, the N systems of signals are combined into one system and one switch is executed. One page's worth of information has been collected.

Since the automatic target detection means detects the target after combining them into one system in this way, only one automatic target detection means is required.
When using the same number of systems as in the prior art, the scale of the comparison hardware can be reduced. The other output of the selector is coupled to video playback means.

The output of the selector appears only once every several bits of N or more due to MDF processing, so it is insufficient as a visual video signal for the operator, so the missing portion of the video signal is modified to be suitable for visual video signals. It is necessary to supplement the video signal.

The video reproduction means generates and interpolates a pseudo video signal for the missing portion based on the input target signal.

This video reproducing means can also be provided after being combined into one system by a selector, and like the automatic target detection means, only one system is required, and it can be easily provided without increasing the hardware.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a functional block diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, a radar apparatus according to the present invention includes a receiving video input terminal 10.
05. A/D converter 200, Doppler filter 301~
30N, LOG/CFAR311~31N, AGC
321 to 32N, a video selector 400, an automatic target detection processor 500, a smoothing video integrator 600, a D/A converter 700, an automatic target detection processing output terminal 800, and a reproduction processing video output terminal 900.

In FIG. 1, the received video is input from an input terminal 100 to an A/D
The signal is input to the converter 200 and applied in parallel to N-channel Doppler filters 301 to 3ON. Here, the Doppler filters 301 to 3ON each have a different pass frequency band and are designed to cover the entire Doppler frequency band with N channels. As a result, various eye source signals and clutter signals having different Doppler frequencies are separated into separate Doppler filters.

Further, the target signal and the clutter signal, which happen to have the same Doppler frequency, pass through the same Doppler filter. In any case, the signal separated for each Doppler frequency is LOG/CF
Average value division processing is performed in AR311 to AR31N.7 Here, clutter signals that spread in the range direction are suppressed to a level equivalent to receiver noise, but target signals that exist only in the form of pulses in the range direction suffer some processing loss. Just cover it and it will pass. In this way, the clutter suppression process is temporarily completed, and the automatic target detection process is started.

In LOG/CFAR processing, various clutter signals are divided by the average level and suppressed. However, since the amplitude distribution characteristics after the suppression processing are not uniform depending on the amplitude distribution characteristics of the clutter signal, the AGL 321
The gain is automatically adjusted at ˜32N, so that the probability of mistaking the remaining effacement for the target is equal, like an N-th channel Doppler filter channel.

Also, this AGC321 to AGC32N is LOG/CFAR
It may be a circuit that detects the maximum value of the residual signal strength in a predetermined range after processing and automatically adjusts the gain so as to provide an attenuation amount proportional to the detected maximum amplitude strength. The N-channel signals whose levels have been adjusted in this way are selected to a maximum value by the video selector 400 and combined into one signal system.

Maximum value selection is performed for each range bin. f & large (directly selected and combined signals are sent to a one-channel automatic target detection processor 500 for target detection processing in the same way as in a conventional radar device that does not use an MDF, and output to an output terminal 80.
Output from 0.

It goes without saying that by using the Weibull CFAR processing means as the CFAR processing means, effective rutter suppression can be obtained for signals that follow a Weibull distribution such as ground clutter.

Further, the maximum value selected and combined signal is subjected to video reproduction processing in a smoothing video integrator 600 in order to reproduce video for visual judgment by a radar monitor (operator).

That is, in this embodiment, since the MDF processing is performed once every N hits, the signal synthesized by the video selector 400 becomes a signal once every N hits.

That is, N-1 hits are missing.

In order to reproduce this missing part, a signal is input once every N hits, and a signal for every N hits is output by interpolating the signals for every N hits through feedback integrator processing.

FIG. 2 is an explanatory diagram showing changes in point target signals due to MDF processing and video playback processing. The same figure (a
) is a diagram showing the amplitude variation of a received video signal from an ideal point target.

FIG. 5B is a diagram showing the amplitude change of the point target after MDF processing is performed on the signal in FIG. 2D for an example of N=5. In other words, there is one signal in every 5 hits, and 4 hits are missing.The 6th time figure (c) is a signal waveform in which the missing part is reproduced with a pseudo signal with the same amplitude as the first arriving signal. . By smoothing the signal obtained in this manner by a feedback integrator, a signal waveform as shown in FIG. 3(d) is obtained which can provide a display suitable for visual judgment by an operator, which is equivalent to the horizontal diagram (a). The processed video signal thus reproduced is D/
The A converter 700 converts the signal into an analog video signal and sends it to the radar display.

(Effects of the Invention) As explained above, the radar device of the present invention synthesizes signals from multiple systems subjected to MDF processing and CFAR processing into one system by selecting one of the systems for each range bin using a selector, and then synthesizes the signals into one system. Since the automatic target detection processing system is designed to detect the target, only one automatic target detection processing system is required and the hardware scale can be significantly reduced compared to the conventional system.

In addition, from the signals combined into one system, the video playback means interpolates the signal of the period missed for MDF processing, thereby providing an optimally processed processed video. The advantage is that radar video can be displayed to leave the decision to the operator.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a conceptual diagram showing changes in point target signals due to MDF processing and video playback processing. 100... Reception video input end, 200...
...A/D converter, 301-3ON...Doppler filter, 311
~31N...LOG/CFAR1321~32
N...AGC1 400...Video selector, 500...
...Automatic target detection processor, 600...
Smoothing video integrator, 700...
- D/A converter, 800... automatic target detection processing output terminal, 900... reproduction processing video output terminal. Agent: Yoshihiro Yahata, Patent Attorney, 1-Invention precedents, side-by-side / Diagram

Claims (4)

[Claims] (1) In a radar device equipped with a multi-Doppler filter as a moving target identification means, there are generally N (an integer greater than 1) Doppler filters; N CFAR processing means for automatically adapting to the amplitude distribution characteristics of the signal and converting and suppressing the signal into a signal having the same amplitude distribution characteristics as the receiver noise; connected to the output ends of the N CFAR processing means; a selector that combines N signals into one signal system by selecting the output signal of one of the CFAR processing means for each distance direction processing unit of the radar; an automatic target detection device connected to the output end of the selector; means; connected to the output end of the selector; M (≧N);
video reproducing means for reproducing the signal for each transmitted pulse by interpolating the Doppler filter output signal once per transmitted pulse; a D/A converter connected to the video reproducing means for generating analog processed video; A radar device comprising: (2) The radar apparatus according to claim (1), wherein the CFAR processing means is a Weibull CFAR processing means capable of converting a signal having a Weibull distribution characteristic as an amplitude characteristic into a CFAR. (3) LO in which the CFAR processing means can convert a signal having Rayleigh distribution characteristics as an amplitude characteristic into CFAR
It is connected to the output ends of the G/CFAR processing means and the LOG/CFAR processing means, and is adapted to the residual signal resulting from the LOG/CFAR processing of a signal whose amplitude characteristic is not a Rayleigh distribution, and is adapted to the amplitude characteristic of the receiver noise signal. The radar device according to claim 1, further comprising automatic gain adjustment means for converting the signal into a signal having an equivalent amplitude distribution characteristic. (4) The automatic gain adjustment means detects the maximum value of the residual signal amplitude strength within a predetermined range after LOG/CFAR processing, and provides an attenuation amount proportional to the detected maximum amplitude strength. The radar device according to claim 3, further comprising automatic gain control means that performs automatic gain adjustment.