JP3781218B2 - Multiband radar apparatus and method and circuit suitable for the same - Google Patents

Description

このような論理にてＡ及びＢを決定したとすると、物標近傍が激しい降雨降雪や激しい波浪に見舞われているときにはＸxav ≧０が成立するため
【数３】
ｙ＝Ｘx ＊Ｘs ＋ΔＸ
となる。Ｘx は物標からの反射波即ち物標信号Ｓx とクラッタ成分Ｃx の和と見なすことができ、またＸs も物標信号Ｓs とクラッタ成分Ｃs の和と見なすことができるから、
【数４】
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
但し、Ｓ／Ｃ｜_X ＝Ｓx ／Ｃx ：Ｘバンド単独でのＳ／Ｃ比
Ｓ／Ｃ｜_S ＝Ｓs ／Ｃs ：Ｓバンド単独でのＳ／Ｃ比
Ｓx 、Ｃx 、Ｓs 及びＣs ：ｔの関数
と表せる。この式の右辺から、この場合のｙにおける物標信号対クラッタ抑圧比即ちＳ／Ｃ比を、
【数５】
Ｓ／Ｃ｜_X ・Ｓ／Ｃ｜_S ＋Ｓ／Ｃ｜_S ＋Ｓ／Ｃ｜_X
と表せることがわかる。一般に、Ｘxav が大きいときにはＳ／Ｃ｜_S ＞Ｓ／Ｃ｜_X ＞１が成り立つから、ｙのＳ／Ｃ比はＳバンド単独でのそれよりも、またＸバンド単独でのそれよりも、大きくなることが分かる。即ち、上のような論理に従いＡ及びＢを決定したときには、各バンド単独でのＳ／Ｃよりも良好なＳ／Ｃを、降雨降雪時及び波浪時に、提供することができる。
【００１８】
逆に、Ｘxav が小さいときには、上の論理から、
【数６】
ｙ＝Ｘx ＊Ｘs ＋（１−Ｘxav ／Ｘ０）＊Ｘx ＋ΔＸ
となる。この式は、Ｘxav が大きいときの式にＸx の項を付加した式である。一般に、Ｘxav が小さくなるのは例えば凪のとき、即ち図５に示した鏡面反射によるマルチパスがＳバンドで顕在化しやすいときであるから、Ｘx の項の導入によって、Ｓバンドレーダに対するＸバンドレーダの利点即ちこのようなマルチパス障害がおきにくいという利点を、確保できる。また、Ｘx の項の係数はＸxav が小さくなると大きくなるから、一般的な傾向として、風雨波浪が小さければ小さいほど、Ｘバンドレーダの利点を強調できる。
【図面の簡単な説明】
【図１】 本発明の一実施形態に係る装置の全体構成を示すブロック図である。
【図２】 この実施形態に含まれる信号処理回路の構成を示すブロック図である。
【図３】 従来の問題点を説明するための図である。
【図４】 従来の問題点を説明するための図である。
【図５】 従来の問題点を説明するための図である。
【図６】 従来の問題点を説明するための図である。
【符号の説明】
１０x ，１０s アンテナ、１２ 駆動部、１８x ，１８s 受信機、２０ 指示部、２３ CA−CFAR回路、２４ 相関回路、２５ 係数回路、２６ 加算回路、Ｘx ，Ｘs ，ｙ レーダビデオ、Ｘxav セルアベレージ、ΔＸ 偏差、Ａ，Ｂ 係数。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radar apparatus that is mounted on a moving body such as a ship and instructs an image of a target existing around the moving body, and in particular, a multiband radar apparatus that uses a plurality of radio frequencies simultaneously, It relates to a method and circuit suitable for the implementation of this device.
[0002]
[Prior art and its problems]
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 information. A radar device is well known as a device that can detect the presence or absence of a target and its position, and indicate an image of the target together with the position on the screen. When a radar device is used, it is generally possible to operate and operate the mobile body more safely and normally than when the radar device is not used.
[0003]
However, when rainfall and snowfall are severe (see FIG. 3) or when waves are generated on the sea surface (see FIG. 4), reflected waves from raindrops or snowflakes (weather clutter) or reflected waves from the sea surface (sea clutter) ) And the like have a relatively high ratio, so that the reflected wave from the target, that is, the target signal is easily buried. In particular, it is likely to be difficult to detect a small target such as a channel buoy at a relatively high radio frequency (for example, X band). On the contrary, when the weather is good and the sea surface is calm (凪), the sea surface is likely to cause specular reflection, so the reflected signal intensity to the sea surface may reduce the received signal strength (see FIG. 5: so-called Multipath failure). Further, depending on the shape of the target, the received signal strength is also lowered by the phase synthesis of the reflected waves from the target (see FIG. 6). In particular, the problem of multipath and phase synthesis is an obstacle to detecting a relatively small target that is at a medium distance or longer at a relatively low radio frequency (for example, S band).
[0004]
In the field of radar devices, various studies have been made on how to deal with clutter. One of the widely used countermeasures against clutter is a circuit or process called CFAR (Constant False Alarm Rate). Roughly speaking, the CFAR is a process of extracting a low frequency component from a polar coordinate type video signal obtained by a radar apparatus, that is, a radar video, and subtracting the extracted low frequency component from the radar video. In general, in a radar video, a component (eg, clutter) that appears at a relatively low level and at any reception time (position) and a component (eg, a target signal) that appears at a relatively high level for a very short time. Therefore, by executing CFAR, it is possible to suppress the false alarm probability, that is, the error probability that a non-target is a target or a target is not a target to a certain level or less. . One CFAR is called CA-CFAR. CA (Cell Averaging) here is a method for extracting low frequency components from radar video as follows: “Mainly focusing on the reception time (position) while changing the reception time (position) of interest along the time axis. The process of “determining the average or weighted average of radar video at a plurality of received times (positions)” is employed. Several reception times (positions) around the reception time (position) of interest are called cells, and the average or weighted average obtained for each cell is called cell average. Regarding CFAR and CA, various prior art documents exist, so please refer to them in the interpretation of the present invention described later.
[0005]
The problems illustrated in FIGS. 3 to 6 cannot be sufficiently mitigated or eliminated even if such a CFAR is simply applied. That is, the problems shown in FIG. 3 and FIG. 4 become prominent when the radio frequency is high, and the problems shown in FIG. 5 and FIG. 6 become prominent 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 that can solve the problems illustrated in FIGS. In the preferred embodiment of the present invention, this objective is achieved through a combination of CFAR and frequency diversity.
[0007]
The radar apparatus according to the present invention is a multiband radar apparatus, that is, a radar apparatus capable of detecting surrounding targets at a plurality of radio frequencies. The multiband radar apparatus according to the present invention includes a first radar unit, a second radar unit, and an instruction unit. Both the first and second radar units generally generate 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 the first radio frequency, and the frequency of the radio signal used by the second radar unit is a different second radio frequency. Accordingly, in the present invention, two types of radar video are obtained, namely, the output of the first radar unit, that is, the first radar video, and the output of the second radar unit, that is, the second radar video. One of the features of the multiband radar apparatus according to the present invention is a multiband radar signal processing circuit incorporated in (or provided with) the instruction unit, or a radar video combining method executed by this circuit. Yes, and more particularly in the generation procedure of the multiband combined radar video in these circuits or methods, i.e. the improved frequency diversity procedure. More particularly, the output of CFAR or CA-CFAR can be used in this frequency diversity procedure.
[0008]
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 multiband combined radar video is generated by combining the weighted correlation value, the weighted first radar video, and the first radar video after the removal of the low frequency component. The generated multiband combined radar video is used to indicate a target image.
[0009]
By executing such a procedure, in the present invention, it is possible to easily solve the problems that are easily manifested according to the level of the radio frequency. For example, it is assumed that the first radio frequency belongs to the X band and the second radio frequency belongs to the S band. Under such a radio frequency design, the problems shown in FIGS. 3 and 4 tend to appear in the first radar video, and the problems shown in FIGS. 5 and 6 tend to appear in the second radar video. On the other hand, when the problems shown in FIGS. 3 and 4 are obvious, the low-frequency component in the first radar video is at a relatively high level. Accordingly, 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 conversely, when the low frequency component is at a relatively low level, the first coefficient is decreased or the second coefficient is decreased. By increasing the coefficient, according to the present invention, any of the problems shown in FIGS. 3 to 6 can be alleviated or eliminated as compared with the prior art. Although specific frequency bands such as the X band and the S band are shown here, it should be noted that this is only an example and can be applied to other bands. In addition, it should be noted that the object of the present invention should not be limited to solving the problems illustrated in FIGS. 3 to 6 because different radio frequency bands have different problems peculiar 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 the correlation circuit and the coefficient circuit, and the correlation circuit and the coefficient circuit each determine the first or second coefficient according to the value of the cell average. Alternatively, the first and second coefficients are further determined by the CA-CFAR circuit. The correlation circuit weights the correlation value between the first radar video and the second radar video with a first coefficient, and the coefficient circuit weights the first radar video with a second coefficient. Finally, using the adder circuit, the first radar video after cell average removal output from the CA-CFAR circuit, the correlation value after weighting with the first coefficient, and the first radar video after weighting with the second coefficient are obtained. , Add and combine. By applying such CA-CFAR technology, a multiband coupled radar video can be suitably generated.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2. First, as shown in FIG. 1, in the present embodiment, for example, an X-band antenna 10x and an S-band antenna 10s are provided at a place with a good view of a ship, and these are collectively rotated by a single drive unit (for example, a motor) 12. ing. Of course, a separate drive unit may be provided for each antenna, and the drive units may be synchronized. The X-band antenna 10x and the S-band antenna 10s are preferably directed in the same direction. However, if the beam direction difference (offset) is known in advance, the offset can be compensated for in the subsequent signal processing. The beam direction may be shifted.
[0012]
The X-band antenna 10x and the S-band antenna 10s are connected to a transmitter 16x or 16s and a receiver 18x or 18s via a transmission / reception switch 14x or 14s, respectively. The duplexers 14x and 14s are members for sharing the corresponding antennas with the corresponding transmitters and receivers. The transmission / reception switches 14x and 14s supply the transmission signals supplied from the corresponding transmitters to the corresponding antennas. The received reflected wave is supplied to the corresponding receiver. When antennas are provided separately for transmission and reception or when only reception is performed, the transmission / reception switchers 14x and 14s can be omitted (for example, only one ship in the fleet transmits and each ship receives). Further, the transmitters 16x and 16s generate the transmission signal by, for example, modulating a carrier wave having a predetermined frequency with a pulse having a predetermined width and a predetermined repetition period (in the case of pulse radar). The receivers 18x and 18s perform amplification, frequency conversion and the like on the reflected wave obtained from the corresponding antenna via the corresponding transmission / reception switch, and the resulting analog radar video Xx (t) or Xs (t) 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 the target image on the CRT screen or the like in the PPI format based on the result.
[0013]
FIG. 2 shows a signal processing circuit for generating a multiband combined radar video y (t) by combining Xx (t) and Xs (t) among the internal circuits of the instruction unit 20, that is, a frequency having a CA-CFAR function. The structure of a diversity circuit is shown. 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) through the analog control circuit 21x into a digital radar video Xx (i). Convert (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 converts Xs (t) through the analog control circuit 21s into digital radar video Xs (i). .
[0014]
The CA-CFAR circuit 23 applies a well-known CA-CFAR to Xx (i), and the cell average Xxav obtained in the course is given to the correlation circuit 24 and the coefficient circuit 25, and the deviation ΔX = Xx (i resulting from the CA-CFAR ) -Xxav is supplied to the adder circuit 26, respectively. 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, respectively. The correlation circuit 24 supplies a value A * Xx (i) * Xs (i) obtained by multiplying the correlation Xx (i) * Xs (i) between Xx (i) and Xs (i) by the coefficient A to the addition circuit 26. To do. The coefficient circuit 25 supplies the addition circuit 26 with a value B * Xx (i) obtained by multiplying Xx (i) by the coefficient B. The adder circuit 26 calculates the sum of A * Xx (i) * Xs (i), B * Xx (i) and ΔX, that is, the multiband coupled radar video y (t), and outputs this to a buffer memory (not shown). Store. 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) on the buffer memory is coordinate-converted by a scan converter and displayed on the screen of a raster scan type indicator.
[0015]
Here, if the gain in the analog control circuit or the A / D converter is ignored, the above processing is
[Expression 1]
y = A * Xx * Xs + B * Xx + ΔX
It can be expressed as. For simplification of description, Xx (t) is omitted 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 represents the relative ratio of clutter contained in the X-band radar video, and therefore becomes large when the rainfall is heavy (FIG. 3), when the sea surface is rough (FIG. 4), etc. . In the present embodiment, by determining A and B based on Xxav, for example, when the vicinity of the target is hit by heavy rain, snow, or heavy waves, the S band radar video is used relatively, and conversely, when it is dredging The y (t) is generated relatively utilizing the X-band radar video.
[0016]
As a specific example, A and B are determined by the following logic. X0 is a constant determined experimentally or empirically.
[0017]
[Expression 2]

Assuming that A and B are determined by such logic, Xxav ≧ 0 holds when the vicinity of the target is hit by heavy rain, snow, or heavy waves.
y = Xx * Xs + ΔX
It becomes. 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.
[Expression 4]
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
However, S / C | _X = Sx / Cx: S / C ratio in X band alone S / C | _S = Ss / Cs: S / C ratio in S band alone Sx, Cx, Ss and Cs: t It can be expressed as a function. From the right side of this equation, the target signal to clutter suppression ratio, that is, the S / C ratio at y in this case,
[Equation 5]
S / C | _X・ S / C | _S + S / C | _S + S / C | _X
It can be expressed that. In general, when Xxav is large, S / C | _S > S / C | _X > 1 holds, so that the S / C ratio of y is larger than that of the S band alone and larger than that of the X band alone. I understand that That is, when A and B are determined according to the above logic, S / C better than S / C of each band alone can be provided at the time of raining and snowing.
[0018]
Conversely, when Xxav is small,
[Formula 6]
y = Xx * Xs + (1-Xxav / X0) * Xx + ΔX
It becomes. This expression is an expression obtained by adding a term of Xx to an expression when Xxav is large. In general, Xxav becomes small, for example, in the case of wrinkles, that is, when the multipath due to specular reflection shown in FIG. 5 is easily manifested in the S band. By introducing the term Xx, the X band radar for the S band radar is introduced. , That is, the advantage that such a multipath failure hardly occurs. Further, since the coefficient of the Xx term increases as Xxav decreases, the general tendency is that the smaller the wind and rain waves, the more the advantage of the X-band radar can be emphasized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a signal processing circuit included in this 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 drive unit, 18x, 18s receiver, 20 indicating unit, 23 CA-CFAR circuit, 24 correlation circuit, 25 coefficient circuit, 26 adder circuit, Xx, Xs, y radar video, Xxav cell average, ΔX Deviation, A, B coefficient.

Claims (5)

By receiving the reflected wave from the transmitted target object radio signals around having a first radio frequency, a first radar unit for generating a first radar video including video and clutter components of the target object,
A second radar signal is generated by transmitting a radio signal having a second radio frequency different from the first radio frequency to the surroundings and receiving a reflected wave from the target, thereby generating a second radar video including an image of the target and a clutter component. A radar unit;
An instruction unit for instructing the image of the Mono漂,
In a radar video combining method, which is used in a multiband radar apparatus having the above , and combines the obtained images of two targets and a radar video including clutter components into one,
A low-frequency extraction step of extracting a low-frequency component serving as a clutter component from the first radar video obtained using the first radio frequency;
A coefficient setting step for variably setting at least one of the first and second coefficients according to the amount of the low frequency component;
A radar video correlation value calculating step of weighting a correlation value between the second radar video and the first radar video obtained by using a second radio frequency different from the first radio frequency by a first coefficient;
A first radar video calculating step of weighting the first radar video by a second coefficient;
A first radar video low frequency removal step of removing low frequency components from the first radar video before weighting;
A radar video addition step of generating a multiband combined radar video by adding the weighted correlation value, the weighted first radar video, and the first radar video after removal of the low frequency component;
A radar video combining method comprising: The first radio frequency belongs to the X band, the second radio frequency belongs to the S band,
In the coefficient setting step, when the low frequency component is higher than a predetermined value, the first coefficient is increased or the second coefficient is decreased. Conversely, when the low frequency component is lower than the predetermined value, the first coefficient is decreased. The radar video combining method according to claim 1, wherein the second coefficient is increased. A CA-CFAR circuit for performing a low frequency extraction step and a first radar video low frequency removal step;
A correlation circuit for executing a procedure for determining the first coefficient and a radar video correlation value calculating step among the coefficient setting steps;
A coefficient circuit for executing a procedure relating to determination of the second coefficient and a first radar video calculating step in the coefficient setting step;
An addition circuit for performing a radar video addition step;
With
3. A signal processing circuit for multiband radar, wherein the radar video combining method according to claim 1 or 2 is executed by cell averaging of the first radar video in the CA-CFAR circuit and use of the result. A CA-CFAR circuit that executes a low-frequency extraction step, a coefficient setting step, and a first radar video low-frequency removal step;
A correlation circuit for performing a radar video correlation value calculating step;
A coefficient circuit for executing a first radar video calculation step;
An addition circuit for performing a radar video addition step;
With
3. A signal processing circuit for multiband radar, wherein the radar video combining method according to claim 1 or 2 is executed by cell averaging of the first radar video in the CA-CFAR circuit and use of the result. A first radar unit that generally generates a first radar video including an image of the target and a clutter component by transmitting a radio signal having a first radio frequency to the surroundings and receiving a reflected wave from the target;
By transmitting a radio signal having a second radio frequency different from the first radio frequency to the surroundings and receiving a reflected wave from the target, a second radar video that generally includes an image of the target and a clutter component is generated. Two radar units;
An instruction unit that has the signal processing circuit for multiband radar according to claim 3 or 4 and indicates an image of a target based on a multiband combined radar video;
A multiband radar device comprising:

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