JPH10170634A - Multiband radar device and method and circuit suitable for this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily eliminate a controversial point at which an actualization degree is different according to a pitch of a frequency by joining a CFAR (constant fails alarm rate) and a frequency diversity. SOLUTION: Analog control circuits 21X and 21S of a signal processing circuit to generate multiband joining radar video y(t) by joining Xx(t) and Xs(t), that is, a frequency diversity circuit having a CA-CFAR function among an indicating part internal circuit, respectively amplify Xx(t) and Xs(t), and perform processing such as the suppression of clutter, and convert them into digital radar video Xx(i) and Xs(i) (i: a discrete value to show time). A CA-CFAR circuit 23 respectively supplies a cell average Xxav obtained by performing a CA-CFAR on the Xx(i) to a correlation circuit 24 and also a deviation (ΔX= Xx(i)-Xxav) being a result of the CA-CFAR to an addition circuit 26. The adddition circuit 26 finds the multiband joining radar video y(t), and outpus/ stores it to/in a buffer memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus mounted on a moving body such as a ship and instructing an image of a target existing around the moving body, and in particular, uses a plurality of radio frequencies simultaneously in parallel. The present invention relates to a multi-band radar device and a method and circuit suitable for implementing the device.

[0002]

2. Description of the Related Art One of the information necessary for the operation and operation of a moving object is an image of a target (for example, another ship, a coastline, a harbor, a buoy, etc.) existing around the moving object. 2. Description of the Related Art A radar device is known as a device capable of detecting the presence or absence of a target and its position and instructing the image of the target along with the position on a screen. In general, when a radar device is used, safer and more normal operation and operation of a mobile body can be performed than when no radar device is used.

However, when rainfall or snowfall is severe (see FIG. 3) or when waves are generated on the sea surface (see FIG. 4), reflected waves (weather clutter) from raindrops and snowflakes and reflections from the sea surface Since the ratio of clutter components such as waves (sea clutter) relatively increases, the reflected wave from the target, that is, the target signal is easily buried. In particular, it tends to be difficult to detect a small target such as a channel buoy at a relatively high radio frequency (for example, X band). Conversely, when the weather is good and the sea surface is calm (calm), the sea surface is likely to cause specular reflection, and the received signal strength may be reduced by the reflected wave traveling down the sea surface (see FIG. 5: so-called). Multipath failure). Further, depending on the shape of the target, the received signal strength is also reduced due to the phase synthesis of the reflected waves from the target (see FIG. 6). In particular, the problems of multipath and phase synthesis hinder the detection of relatively small targets at intermediate distances or more at relatively low radio frequencies (eg, S band).

[0004] In the field of radar devices, various studies have been made on how to prevent clutter. One of widely used countermeasures against clutter is a circuit or process called CFAR (Constant False Alarm Rate). CFAR is, roughly speaking,
This is a process of extracting low-frequency components from a polar coordinate type video signal obtained by a radar device, that is, radar video, and subtracting the extracted low-frequency components from the radar video. In general, components (for example, clutter) that appear at a relatively low level and appear at any reception time (position) in radar video
And a component (for example, a target signal) appearing at a relatively high level for a very short time, the probability of false alarm, that is, a target that is not a target is set as a target by executing CFAR. Can be suppressed to a certain level or less. One of the CFARs is called CA-CFAR. CA (Cel)
l Averaging) is a method of extracting the low-frequency component from radar video. "Averaging), while sequentially changing the target reception time (position) along the time axis,
To find the average or weighted average of the radar video at several reception times (positions) centered on the... Several reception times (positions) centered on the reception time (position) of interest. Is called a cell, and the average or weighted average obtained for each cell is called a cell average.Because there are various prior art documents regarding CFAR and CA, in interpreting the present invention described later, See also those.

[0005] The problems exemplified in FIGS. 3 to 6 cannot be sufficiently mitigated or eliminated even by simply applying such CFAR. That is, the problems shown in FIGS. 3 and 4 are significant when the radio frequency is high, and the problems shown in FIGS. 5 and 6 are significant when the radio frequency is low. CFAR is no longer effective enough.

[0006]

SUMMARY OF THE INVENTION One of the objects of the present invention is to realize a radar apparatus which can solve the problems exemplified in FIGS. In a preferred embodiment of the invention, this object is achieved by a combination of CFAR and frequency diversity.

[0007] The radar apparatus according to the present invention is a multi-band radar apparatus, that is, a radar apparatus capable of detecting surrounding targets using a plurality of radio frequencies. A multi-band radar device according to the present invention includes a first radar unit, a second radar unit, and an instruction unit. Each of the first and second radar units generally generates a radar video including an image of the target and a clutter component by transmitting a radio signal to the surroundings and receiving a reflected wave from the target. However, the frequency of the radio signal used by the first radar unit is a first radio frequency, and the frequency of the radio signal used by the second radar unit is a second radio frequency different from the first radio frequency. Therefore, in the present invention, the output of the first radar unit, ie, the first radar video, and the output of the second radar unit, ie, the second
Two types of radar video, radar video, are obtained.
One of the features of the multiband radar device according to the present invention is as follows.
A signal processing circuit for a multi-band radar incorporated in (or attached to) the indicating unit or a radar video combining method executed by the circuit, and more specifically, a multi-band radar in these circuits or methods. There is a combined radar video generation procedure, ie, an improved frequency diversity procedure. More specifically, the output of CFAR or CA-CFAR can be used in this frequency diversity procedure.

In the present invention, the low-frequency component is extracted from the first radar video, and at least one of the first and second coefficients is variably set according to the amount of the extracted low-frequency component. Further, the correlation value between the second radar video and the first radar video is weighted by the first coefficient, and the first radar video is weighted by the second coefficient. On the other hand, low frequency components are removed from the first radar video before weighting. Then, a multi-band combined radar video is generated by combining the correlation value after the weighting, the first radar video after the weighting, and the first radar video after the low-frequency component removal. The generated multi-band combined radar video is used for indicating a target image.

By executing such a procedure,
In the present invention, it is possible to easily solve the problem that the easiness of occurrence differs depending on the level of the radio frequency. For example, it is assumed that the first radio frequency is designed to belong to the X band and the second radio frequency is designed to belong to the S band. Under such a radio frequency design, the problems shown in FIGS. 3 and 4 are likely to appear in the first radar video, and FIG.
And the problems shown in FIG. 6 tend to appear in the second radar video. On the other hand, when the problems shown in FIGS. 3 and 4 become apparent, the low-frequency component in the first radar video becomes relatively high. Therefore, when the low frequency component extracted from the first radar video is at a relatively high level, the first coefficient is increased or the second coefficient is decreased, and when the low frequency component is relatively low, the first coefficient is decreased or the second coefficient is decreased. By increasing the coefficient, according to the present invention, any of the problems in FIGS. 3 to 6 can be alleviated or eliminated as compared with the related art. Although specific frequency bands such as the X band and the S band are shown here, it should be noted that this is merely an example and can be applied to other bands. further,
It should also be noted that the objects of the present invention should not be limited to solving the problems exemplified in FIGS. 3 to 6, since different radio frequency bands have different problems unique to the frequency bands.

[0010] The multiband combined radar video generation procedure according to the present invention can be suitably realized by using a CA-CFAR circuit. For example, the cell average generated by the CA-CFAR circuit is supplied to a correlation circuit and a coefficient circuit, and each of the correlation circuit and the coefficient circuit determines the first or second coefficient according to the value of the cell average. Alternatively, the first and second coefficients are further determined in the CA-CFAR circuit. The correlation circuit weights the correlation value between the first radar video and the second radar video with the first coefficient, and the coefficient circuit weights the first radar video with the second coefficient. Finally, the first radar video after cell average removal, the correlation value after weighting by the first coefficient, and the first radar video after weighting by the second coefficient are output from the CA-CFAR circuit using an addition circuit. , And add them together. By applying such CA-CFAR technology, a multi-band combined radar video can be suitably generated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS. First, as shown in FIG. 1, in the present embodiment, for example, an X band antenna 10x and an S band antenna 1
0s, which are combined into a single drive (eg, motor) 1
2 rotate it all at once. Of course, a separate drive unit may be provided for each antenna, and each drive unit may be synchronized. Although it is preferable that the beams of the X band antenna 10x and the S band antenna 10s are directed in the same direction, the difference (offset) in the beam direction is determined in advance.
If is known, the offset can be compensated for in the subsequent signal processing, so that the beam direction may be shifted.

The X-band antenna 10x and the S-band antenna 10s are connected to a transmitter 16x or 16s and a receiver 18x or 18 via a duplexer 14x or 14s, respectively.
connected to s. The transmission / reception switchers 14x and 14s are members for sharing the corresponding antenna with the corresponding transmitter and receiver, supplying the transmission signal supplied from the corresponding transmitter to the corresponding antenna, and using the corresponding antenna. The received reflected wave is supplied to a corresponding receiver. When the antennas are provided separately for transmission and reception or when only reception is performed, the transmission / reception switches 14x and 14s can be omitted (for example, an application in which only one of the fleets transmits and each of the vessels receives). Also, the transmitters 16x and 16s
Generates the transmission signal by modulating a carrier having a predetermined frequency with a pulse having a predetermined width and a predetermined repetition period (in the case of a pulse radar). Receivers 18x and 18
s performs amplification, frequency conversion, and the like on the reflected wave obtained from the corresponding antenna via the corresponding duplexer, and converts the resulting analog radar video Xx (t) or Xs (t) into
The signal is supplied to the instruction unit 20 (t is the reception time of the reflected wave). The instruction unit 20 combines Xx (t) and Xs (t), and displays an image of the target on a CRT screen or the like, for example, in a PPI format based on the result.

FIG. 2 shows an internal circuit of the instructing section 20 which includes X
1 shows the configuration of a signal processing circuit for generating a multiband combined radar video y (t) by combining x (t) and Xs (t), that is, a frequency diversity circuit having a CA-CFAR function. In the figure, an analog control circuit 21x performs processing such as amplification and clutter suppression on Xx (t), and an A / D converter 22x converts Xx (t) passed through the analog control circuit 21x into a digital radar video signal Xx (t).
Convert to x (i) (i: discrete value representing time). Similarly, the analog control circuit 21s performs processing such as clutter suppression on Xs (t), and the A / D converter 22s performs processing on the analog control circuit 2s.
Xs (t) converted from 1s is converted to digital radar video Xs (i).

The CA-CFAR circuit 23 includes a well-known CA-CF in Xx (i).
AR is performed, and the cell average Xxav obtained in the process is supplied to the correlation circuit 24 and the coefficient circuit 25, and the deviation ΔX = Xx (i) −Xxav, which is the result of CA-CFAR, is supplied to the addition circuit 26. Instead of Xxav, the coefficient A determined based on Xxav may be supplied to the correlation circuit 24, and the coefficient B determined based on Xxav may be supplied to the coefficient circuit 25. The correlation circuit 24 calculates a correlation Xx (i) * between Xx (i) and Xs (i).
The value A * Xx (i) * Xs (i) obtained by multiplying Xs (i) by the coefficient A is supplied to the adding circuit 26. The coefficient circuit 25 calculates the coefficient B in Xx (i).
Is supplied to the adding circuit 26. The addition circuit 26 calculates A * Xx (i) * Xs (i), B * Xx (i) and Δ
The sum of X, that is, the multiband combined radar video y (t) is obtained, and this is output and stored in a buffer memory (not shown). An image based on the radar video y (t) on the buffer memory is displayed on the screen of the instruction unit 20. For example,
The radar video (sweep data) in the buffer memory is subjected to coordinate conversion by a scan converter and displayed on a screen of a raster scan type indicator.

Here, if the gain in the analog control circuit and the A / D converter is ignored, the above processing becomes

Y = A * Xx * Xs + B * Xx + .DELTA.X For simplification of description, Xx
(t) is abbreviated, for example, as Xx. As can be understood from this equation, if A is relatively large, the correlation component Xx * Xs appears strongly in y, and if B is large, the X-band radar video Xx appears strongly in y. On the other hand, Xxav
Since the relative ratio of clutter included in the X-band radar video is shown, it becomes large when rainfall and snowfall are severe (FIG. 3) and when the sea surface is rough (FIG. 4). In the present embodiment, by determining A and B based on Xxav, for example, when the vicinity of the target is being hit by severe rainfall or snowfall or strong waves, the S band radar video is relatively utilized, and conversely, when the target is calm. Y (t) is generated by relatively utilizing the X-band radar video.

As a specific example, an example in which A and B are determined by the following logic will be described. X0 is a constant determined experimentally or empirically.

[0017]

A = 1 (always) B = 0 (when Xxav ≧ 0) = 1−Xxav / X0 (when Xxav <0) If A and B are determined by such a logic, the target is Xxav ≧ 0 is satisfied when the neighborhood is under heavy rainfall or snowfall

## EQU3 ## y = Xx * Xs + .DELTA.X. Xx can be regarded as the sum of the reflected wave from the target, that is, the target signal Sx and the clutter component Cx, and Xs can also be regarded as the sum of the target signal Ss and the clutter component Cs.

Xx * Xs = (Sx + Cx) * (Ss + Cs) = Sx * Ss + Cx * Ss + Sx * Cs + Cx * Cs = {S / C | _X * S / C | _S + S / C | _S + S / C | _X + 1 @ * Cx * Cs, where S / C | _X = Sx / Cx: S in X band alone
/ C ratio S / C | _S = Ss / Cs: S / C ratio Sx, Cx, Ss, and Cs in the S band alone. From the right side of this equation, the target signal-to-clutter suppression ratio, or S / C ratio, at y in this case is

It can be seen that S / C | _X · S / C | _S + S / C | _S + S / C | _X In general, when Xxav is large, S / C | _S > S / C | _X > 1 holds, so that S of y
It can be seen that the / C ratio is greater than that of the S band alone and that of the X band alone. That is, when A and B are determined according to the above logic, a better S / C than the S / C of each band alone can be provided at the time of rain, snow, and waves.

Conversely, when Xxav is small, from the above logic,

Y = Xx * Xs + (1-Xxav / X0) * Xx + [Delta] X This equation is obtained by adding the term of Xx to the equation when Xxav is large. In general, Xxav becomes small when, for example, calm, that is, when multipath due to specular reflection shown in FIG.
By introducing the term x, the advantage of the X-band radar over the S-band radar, that is, the advantage that such multipath failure is unlikely to occur, can be secured. Also, since the coefficient of the term Xx increases as Xxav decreases, the general tendency is that the smaller the wind and rain waves, the more the advantages of the X-band radar can be emphasized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a signal processing circuit included in the embodiment.

FIG. 3 is a diagram for explaining a conventional problem.

FIG. 4 is a diagram for explaining a conventional problem.

FIG. 5 is a diagram for explaining a conventional problem.

FIG. 6 is a diagram for explaining a conventional problem.

[Explanation of symbols]

10x, 10s antenna, 12 drivers, 18x, 1
8s receiver, 20 indicator, 23 CA-CFAR circuit, 24
Correlation circuit, 25 coefficient circuit, 26 addition circuit, Xx,
Xs, y radar video, Xxav cell average, Δ
X deviation, A, B coefficient.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masanori Sudo 5-1-1 Shimorenjaku, Mitaka City, Tokyo Japan Radio Co., Ltd. (72) Inventor Shuichi Hashimoto 5-1-1 Shimorenjaku, Mitaka City, Tokyo Japan Radio Inside the corporation

Claims (5)

[Claims] 1. A first step of extracting a low frequency component from a first radar video obtained using a first radio frequency, and at least one of a first and a second coefficient is reduced to an amount of the low frequency component. Variably setting the correlation value between the second radar video obtained using the second radio frequency different from the first radio frequency and the first radar video using the first coefficient. A third step, a fourth step of weighting the first radar video with the second coefficient, a fifth step of removing the low frequency component from the first radar video before weighting, a correlation value after weighting, The first radar video after weighting,
And a sixth step of generating a multi-band combined radar video by combining the first radar video after removing the low-frequency component, and a sixth step. 2. The first radio frequency belongs to the X band, and the second radio frequency belongs to the S band. In the second step, when the low frequency component is at a relatively high level, the first coefficient is increased. 2. The method according to claim 1, wherein the first coefficient is reduced or the second coefficient is increased when the second coefficient is relatively low. 3. A CA for executing the first and fifth steps.
A CFAR circuit, a procedure for determining the first coefficient in the second step and a correlation circuit for executing the third step, a procedure for determining the second coefficient in the second step, and the fourth step And a coefficient circuit for executing
An addition circuit for executing the steps, wherein the CA-CFAR
3. A signal processing circuit for a multi-band radar, wherein the radar video combining method according to claim 1 or 2 is performed by cell averaging of the first radar video in a circuit and utilizing the result. 4. A CA-CFAR circuit for executing the first, second and fifth steps, a correlation circuit for executing the third step, a coefficient circuit for executing the fourth step, and a sixth step. And an addition circuit for performing the above-mentioned CA−
A signal processing circuit for a multi-band radar, wherein the radar video combining method according to claim 1 or 2 is performed by cell averaging of the first radar video in a CFAR circuit and utilizing the result. 5. A first method for transmitting a radio signal having a first radio frequency to the surroundings and receiving a reflected wave from a target to generate a first radar video generally including an image of the target and clutter components. A radar unit that transmits a radio signal having a second radio frequency different from the first radio frequency to the surroundings and receives a reflected wave from the target, thereby generally including a video and a clutter component of the target. A second radar unit for generating a video, and an instruction unit having the signal processing circuit for a multi-band radar according to claim 3 or 4, and instructing an image of a target based on the multi-band combined radar video. Characteristic multi-band radar device.