JP3476737B2 - Inverse synthetic aperture radar and method of generating inverse synthetic aperture radar image - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverse synthetic aperture radar (ISAR) and a method of generating an inverse synthetic aperture radar image (ISAR image), and more particularly to an electronic inverse search function (ECC).
The present invention relates to an inverse synthetic aperture radar utilizing the M function) and a method for generating an inverse synthetic aperture radar image.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional inverse synthetic aperture radar (IS
The conceptual diagram for demonstrating operation | movement of (AR) is shown. In FIG. 5, the target 1 is an object for ISAR processing, and the radar 2 is a conventional ISAR. The radar 2 emits a transmission pulse to the target 1 at a constant repetition frequency and a constant transmission frequency, as indicated by an arrow Y1. Also,
The radar 2 receives the returning radio wave as shown by an arrow Y2 after being reflected by the target 1, for a certain period of time, and subjects the received signal to ISAR processing to obtain an ISAR image of the target 1.

FIG. 6 is a block diagram of an ISAR processing section of the radar 2. As shown in FIG. 6, the conventional ISA
The R (radar 2) includes a velocity component compensator 3 and an acceleration component compensator 4. The signal received by the radar 2 is input to the velocity component compensator 3. Velocity component compensator 3
And the acceleration component compensator 4 subjects the input signal to the processing to be described later and outputs it. The radar 2 generates an ISAR image based on the signal output from the acceleration component compensator 4.

FIG. 7A shows an example of the locus of the distance between the target 1 and the radar 2 directly detected from the received signal of the radar 2 when the target 1 has a velocity component. Figure 7
As shown in (A), when the target object 1 has a velocity component, the distance between the target object 1 and the radar 2 changes with the passage of time. That is, when the target 1 has a velocity component, the radar 2 receives a signal in which the velocity component is reflected.

In order to obtain an ISAR image, it is necessary that the influence of the velocity component of the target 1 is eliminated from the signal that is the basis of the ISAR image. The velocity component compensating unit 3 described above performs a compensation process for eliminating the influence of the velocity component of the target 1 from the signal received by the radar 2 in order to meet the above request. That is, the velocity component compensator 3 performs compensation processing on the input signal so that the relative distance between the target 1 and the radar 2 becomes constant as shown in FIG. 7 (B).

When the target 1 has an acceleration component, the signal after elimination of the velocity component (hereinafter referred to as "velocity compensation signal"), that is, the signal corresponding to FIG.
By performing the FT processing, it is possible to obtain the change component of the Doppler frequency that occurs with the change in the relative distance between the target 1 and the radar 2. FIG. 8A is an example of changes in the Doppler frequency obtained as a result of the above FFT processing. Thus, when the target object 1 has an acceleration component, the acceleration component is reflected in the velocity compensation signal.

In order to obtain the ISAR image, it is necessary that the influence of the acceleration component of the target object 1 is excluded from the signal that is the basis of the ISAR image. The acceleration component compensating unit 4 described above performs a compensation process for eliminating the influence of the acceleration component of the target object 1 from the velocity compensation signal output from the velocity component compensating unit 3 in order to meet the above requirement. That is, the acceleration component compensator 4
The velocity compensation signal is subjected to compensation processing so that the Doppler frequency superimposed on the signal output from the acceleration component compensating unit 4 becomes constant as shown in FIG. 8B. Hereinafter, the signal output from the acceleration component complement unit 4 is referred to as a “speed / acceleration compensation signal”.

From the velocity / acceleration compensation signal obtained by the above processing, the influence of the velocity component of the target 1 and the influence of the acceleration component are excluded. That is, the velocity / acceleration compensation signal is similar to the signal obtained when the target 1 is stationary with respect to the radar 2, that is, the signal including only the fluctuation component of the target 1. The radar 2 performs FFT processing on the velocity / acceleration compensation signal to obtain an ISAR image representing the target fluctuation component.

[0009]

As described above, the radar 2
In order to generate an ISAR image, it is necessary to transmit radio waves to the target 1 for a certain period of time. The target 1 has a function of analyzing a radio wave transmitted from the radar 2 to generate an interfering radio wave, that is, an electronic counter-search function (ECM function).
Some are equipped with. In the conventional ISAR, when the target 1 has an ECM function and the target 1 emits an interference radio wave, an ISAR image may not be properly generated.

FIG. 9A shows an example of the Doppler frequency detected by the radar 2 when the target 1 generates an interference radio wave. As shown in FIG. 9A, when the target object 1 generates an interfering radio wave, the radar 2 detects the frequency of the interfering radio wave as a Doppler frequency in addition to the Doppler frequency indicating the state of the target object 1. In this case, the acceleration component compensator 4 may perform compensation processing such that the interference frequency becomes constant, as shown in FIG. 9B. With such compensation processing, the Doppler frequency representing the state of the target 1 cannot be made constant. Therefore, the radar 2
Then, a situation occurs in which an ISAR image of the target object 1 cannot be obtained.

The present invention has been made to solve the above problems, and provides an ISAR capable of properly obtaining an ISAR image of a target even in an environment where an interfering radio wave is emitted. This is the first purpose. Also,
The present invention has been made in order to solve the above problems, and it is a first object of the present invention to provide an ISAR image generation method for appropriately obtaining an ISAR image of a target object in an environment where interference waves are emitted. The purpose of.

[0012]

The invention according to claim 1 is
An inverse synthetic aperture radar that generates an image of a target object based on a series of received pulses, and an ECCM function unit that changes the characteristics of a transmission pulse according to a predetermined rule, and a compensation process in consideration of the predetermined rule. Accordingly, a compensation processing unit that converts a series of received pulses into pulses having the constant characteristic is provided.

The invention according to claim 2 is the inverse synthetic aperture radar according to claim 1, wherein the ECCM function section includes a frequency agility function section for changing the frequency of the transmission pulse in accordance with a predetermined rule, and the compensation is performed. The processing unit is characterized by including a frequency compensation processing unit that performs a compensation process for eliminating the influence of the frequency change of the transmission pulse from the reception pulse.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the inverse synthetic aperture radar described above, the ECCM function unit includes a PRF stagger function unit that changes a pulse repetition frequency of a transmission pulse according to a predetermined rule, and the compensation processing unit changes the pulse repetition frequency of a reception pulse from the pulse repetition frequency. It is characterized by comprising a PRF compensation processing unit for performing compensation processing for eliminating the influence of changes.

The invention according to claim 4 is the inverse synthetic aperture radar according to any one of claims 1 to 3, wherein the velocity component and the acceleration component of the target are calculated from the output signal of the compensation processing section. ISAR processing unit for eliminating influence, and the IS
An image generation unit that performs an FFT process on an output signal of the AR processing unit to generate an image of the target object is further provided.

According to a fifth aspect of the present invention, there is provided an inverse synthetic aperture radar image generation method for generating an image of a target object based on a series of received pulses. The ECCM changes the characteristics of the transmission pulse according to a predetermined rule. And a compensation processing step of converting a series of received pulses into pulses having the constant characteristic by performing compensation processing in consideration of the predetermined rule.

According to a sixth aspect of the present invention, there is provided a method of generating an inverse synthetic aperture radar image according to the fifth aspect, wherein the ECCM is used.
The step includes a frequency agility step of changing the frequency of the transmission pulse according to a predetermined rule, and the compensation processing step includes a frequency compensation processing step of performing a compensation processing for eliminating the influence of the frequency change of the transmission pulse from the reception pulse. It is characterized by that.

The invention according to claim 7 is the invention according to claim 5 or 6.
The method for generating an inverse synthetic aperture radar image according to claim 1, wherein the ECCM step includes a PRF stagger step for changing a pulse repetition frequency of a transmission pulse according to a predetermined rule, and the compensation processing step includes the pulse repetition from the reception pulse. It is characterized by including a PRF compensation processing step for performing a compensation processing for eliminating the influence of the frequency change.

The invention according to claim 8 is the method for generating an inverse synthetic aperture radar image according to any one of claims 5 to 7, wherein the target object is obtained from the output signal obtained by the compensation processing step. Further including an ISAR processing step of eliminating the influence of the velocity component and the acceleration component of the above, and an image generation step of performing FFT processing on the output signal obtained in the ISAR processing step to generate the image of the target object. It is a feature.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that elements common to each drawing are denoted by the same reference numerals, and redundant description will be omitted.

Embodiment 1. FIG. 1 shows the principle of ISAR of the present invention. The ISAR shown in FIG. 1 includes an antenna 10 that emits a transmission pulse to a target object and receives a reflected signal generated by the target object. A circulator 12 is connected to the antenna 10. The circulator 12 supplies the transmission pulse generated in the ISAR transmission system to the antenna 10 and supplies the signal received by the antenna 10 to the ISAR reception system.

The circulator 12 is supplied with a transmission pulse from the ECCM function unit 14. The ECCM functional unit is
It has a function of changing the characteristics of the transmission pulse transmitted from the antenna 10 according to a predetermined rule. If the characteristics of the transmission pulse change in this way, the target cannot easily analyze the characteristics of the transmission pulse emitted from the ISAR even if it has the ECM function. Therefore, according to the ISAR of the present embodiment, even when the target object has the ECM function, it is possible to receive the reception pulse caused by the transmission pulse generated by itself without being confused with the interfering radio wave.

The signal received by the antenna 10 is supplied to the ECCM compensation processing section 16 via the circulator 12. In the present embodiment, the ECCM function unit 14 is used for the reception pulse caused by the transmission pulse emitted from ISAR.
The change in characteristics due to the function of is superposed. ECCM
The compensation processing unit 16 is a unit for compensating for the above-mentioned characteristic change superimposed on the received pulse. Therefore, the blocks after the compensation processing unit 16 can perform the predetermined processing based on the pulse having the constant characteristic.

The signal processed by the ECCM compensation processing unit 16 is supplied to the ISAR processing unit 18. The ISAR processing unit 18 includes a velocity component compensating unit 3 and an acceleration component compensating unit 4, which are also mounted on the conventional ISAR (see FIG. 6). The velocity component compensating unit 3 and the acceleration component compensating unit 4 perform the same compensation processing as in the case of the conventional ISAR, that is, compensation for eliminating the influence caused by the velocity component or the acceleration component of the target from the received pulse. Processing (see FIGS. 7 and 8) is performed.

According to the compensation processing of the ISAR processing section 18,
Even when the target has a velocity component and an acceleration component, it is possible to generate a signal obtained when the target is stationary, that is, a signal that reflects only the swaying state of the target. The ISAR of the present embodiment generates an ISAR image by performing FFT processing on the signal thus obtained.

As described above, the ISAR according to the present embodiment properly recognizes the received pulse caused by the transmitted pulse generated by itself even under the environment where the jamming radio wave exists, and properly performs the ISAR.
Images can be generated. Therefore, I of the present embodiment
According to SAR, even when the target has the ECM function, it is possible to properly generate the ISAR image of the target.

Embodiment 2. Next, the ISAR of this embodiment will be described with reference to FIG. FIG. 2 shows a block diagram of the ISAR of this embodiment. IS of this embodiment
The AR is a more specific version of the ISAR of the first embodiment, and uses the frequency agility function as the ECCM function.

That is, the ISAR of this embodiment is shown in FIG.
A frequency agility function unit 20 is provided in place of the ECCM function unit 14 shown in FIG. 1 and a frequency compensation processing unit 22 is provided in place of the compensation processing unit 16 shown in FIG. The frequency agility function unit 20 has a function of changing the frequency of the transmission pulse emitted toward the target according to a predetermined rule. On the other hand, the frequency compensation processing unit 22 performs the compensation processing in consideration of the frequency change of each pulse received by the antenna 10, more specifically, the phase generated between the reception pulses due to the frequency change of the transmission pulses. Perform processing to compensate for changes.

Below, the frequency agility function unit 20
A case where the following two types of frequencies are alternately used for each pulse will be described. In the following equation, C is the speed of light. Frequency 1 = F ₁ (wavelength = λ ₁ = C / F ₁ ) (1) Frequency 2 = F ₂ (wavelength = λ ₂ = C / F ₂ ) (2)

When the distance between the target and ISAR is R, the phase of the received pulse at the position of the antenna 10 is
Each of the frequency 1 (F1) and the frequency 2 (F2) can be expressed by the following equation. Phase φ ₁ = 4πR / λ ₁ (3) Phase φ ₂ = 4πR / λ ₂ (4)

Phase φ ₁ corresponding to frequency 1 (F1),
From the expressions (3) and (4), the relationship of the following expression is established between the phase φ ₂ corresponding to the frequency 2 (F2). λ ₁ · φ ₁ = φ ₂ · λ ₂ (5)

The phase φ ₁ can be expressed by the following equation using I ₁ which is the real number component of the reception pulse corresponding to the transmission pulse of frequency ₁ and Q ₁ which is the imaginary number component thereof. φ ₁ = tan ⁻¹ (Q ₁ / I ₁ ) (6)

Similarly, the phase φ ₂ can be expressed by the following equation using I ₂ which is the real number component of the received pulse corresponding to the transmitted pulse of frequency ₂ and Q ₂ which is the imaginary number component thereof. . φ ₂ = tan ⁻¹ (Q ₂ / I ₂ ) ... (7)

From the expressions (5), (6) and (7), the following relationships are established. Q ₁ / I ₁ = tan (λ ₂ / λ ₁ tan ⁻¹ (Q ₂ / I ₂ )) (8)

Here, if I ₁ = I ₂ is set for convenience of explanation, then Q ₁ = I ₂ · tan (λ ₂ / λ ₁ · tan ⁻¹ (Q ₂ / I ₂ )) (9) , The received signals I ₂ and Q ₂ at frequency ₂ can be converted into the received signals I ₁ and Q _{1 at} frequency 1. In the case where I ₁ = I ₂ is not satisfied, the expression (9) of I ₂ I ₂ 'replaced with = I _1, and the Q ₂ Q _2' replaced by _{= I 1 / I 2 × Q} 2 Therefore, I ₂ and Q
The same conversion can be achieved while preserving the phase of ₂ .

As described above, the ISAR of this embodiment can emit a transmission pulse using a plurality of frequencies.
Therefore, according to the ISAR of this embodiment, the target object is E
Even in the case of having the CM function, it is possible to receive the reception pulse caused by the transmission pulse generated by itself without being confused with the interference radio wave. In addition, the ISA of the present embodiment
In the frequency compensation processing unit 22, R can convert received pulses corresponding to a plurality of frequencies into a signal corresponding to a single frequency. Therefore, the ISA of the present embodiment
According to R, even when the target has the ECM function, it is possible to properly generate the ISAR image of the target.

Embodiment 3. Next, the ISAR of this embodiment will be described with reference to FIGS. 3 and 4. Figure 3
FIG. 3 shows a block diagram of ISAR of the present embodiment. The ISAR of this embodiment is a more specific version of the ISAR of the first embodiment, and uses a pulse recurrence frequency (PRF) stagger function as an ECCM function.

That is, the ISAR of this embodiment is shown in FIG.
1 is provided with a PRF stagger function unit 24 in place of the ECCM function unit 14 shown in FIG. 1, and a peripheral PRF compensation processing unit 26 is provided in place of the compensation processing unit 16 shown in FIG. The PRF stagger function unit 24 has a function of changing the repetition frequency of a pulse emitted toward a target object according to a predetermined rule. On the other hand, the PRF compensation processing unit 26 uses the antenna 10
A process of compensating for the PRF change of the received pulse received in step 1 and converting the received pulse into a signal obtained when the PRF is constant is executed.

A case where the PRF stagger function section 24 alternately uses two types of PRF for each pulse will be described below with reference to FIG. FIG. 4A shows the timing at which a transmission pulse is emitted from ISAR. Here, as shown in FIG. 4A, it is assumed that the pulse interval a and the pulse interval b are used in correspondence with two types of PRF. Further, FIG. 4B shows sampling points before and after the PRF compensation process.

In the process of generating the ISAR image, the FFT process is applied to the video data in the pulse direction. Therefore, the signal that is the basis of the processing has a fixed PRF.
It is necessary to include the pulses generated in 1), that is, the pulses generated at regular intervals. For example, consider a constant sampling cycle in which the maximum and minimum values of the amplitude are taken for the waveform shown in FIG. The black circles and black triangles shown in FIG. 4B indicate sampling points corresponding to this sampling period. In order to generate an ISAR image, the pulse included in the signal that is the basis of the ISAR image needs to correspond to the sampling points indicated by ● or ▲.

As shown in FIG. 4A, when the intervals a and b are alternately used as the intervals of the transmission pulse,
Corresponding to these pulses, the black circles and the white circles shown in FIG. 4B are sampling points. In this case, in order to obtain an ISAR image, it is necessary to convert the sampling point ◯ into the sampling point ▲. In the present embodiment, the PRF compensation processing unit 26 measures the amplitude change of the signal received at the plurality of sampling points, and calculates the signal amplitude at the sampling point ▲ based on the measured value. Therefore, IS
The blocks after the AR processing unit 18 can appropriately generate the ISAR image based on the signal obtained at a constant sampling period.

As described above, the ISAR of this embodiment can emit a transmission pulse using a plurality of PRFs.
Therefore, according to the ISAR of this embodiment, the target object is E
Even in the case of having the CM function, it is possible to receive the reception pulse caused by the transmission pulse generated by itself without being confused with the interference radio wave. In addition, the ISA of the present embodiment
In the R, the PRF compensation processing unit 26 can convert the reception pulse having the changing PRF into a signal having a constant sampling cycle. Therefore, according to the ISAR of this embodiment, an ISAR image of the target can be properly generated even when the target has the ECM function.

[0043]

Since the present invention is constructed as described above, it has the following effects. Claim 1
Further, according to the invention described in 5, it is possible to change the characteristic of the transmission pulse by using the ECCM function and eliminate the change in the characteristic from the received signal.
Therefore, according to the present invention, even in an environment where there is an interfering radio wave, a reception pulse caused by a transmission pulse generated by the device is accurately captured, and an inverse synthetic aperture radar image is appropriately obtained based on the reception pulse. Can be generated.

According to the invention of claim 2 or 6, E
A frequency agility function can be used as the CCM function. Therefore, according to the present invention, even in an environment where there is an interfering radio wave, a reception pulse caused by a transmission pulse generated by the device is accurately captured, and an inverse synthetic aperture radar image is appropriately obtained based on the reception pulse. Can be generated.

According to the invention of claim 3 or 7, E
The PRF stagger function can be used as the CCM function. Therefore, according to the present invention, even in an environment where there is an interfering radio wave, a reception pulse caused by a transmission pulse generated by the device is accurately captured, and an inverse synthetic aperture radar image is appropriately obtained based on the reception pulse. Can be generated.

According to the fourth or eighth aspect of the present invention, the inverse synthetic aperture radar image of the target can be properly generated based on the signal processed by the compensation processing section.

[Brief description of drawings]

FIG. 1 is a block diagram of ISAR according to a first embodiment of the present invention.

FIG. 2 is a block diagram of ISAR according to a second embodiment of the present invention.

FIG. 3 is a block diagram of ISAR according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a state in which two types of PRFs are alternately used and sampling points at that time.

FIG. 5 is a diagram showing a positional relationship between a target object and ISAR.

FIG. 6 is a block diagram of an ISAR processing unit included in a conventional ISAR.

FIG. 7 is a diagram for explaining a function of a velocity component compensator included in a conventional ISAR.

FIG. 8 is a diagram for explaining a function of an acceleration component compensator included in a conventional ISAR.

FIG. 9 is a diagram for explaining a problem of the conventional ISAR.

[Explanation of symbols]

3 velocity component compensation unit, 4 acceleration component compensation unit,
10 antenna, 12 circulator, 14
ECCM function unit, 16 compensation processing unit, 18 IS
AR processing unit, 20 frequency agility function unit,
22 frequency compensation processing unit, 24 PRF stagger function unit, 26 PRF compensation processing unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95

Claims (8)

(57) [Claims] 1. An inverse synthetic aperture radar for generating an image of a target object based on a series of received pulses, the EC changing a characteristic of a transmission pulse according to a predetermined rule.
By performing a compensation process in consideration of the CM function unit and the predetermined rule,
An inverse synthetic aperture radar, comprising: a compensation processing unit that converts a series of received pulses into a pulse having the constant characteristic. 2. The ECCM function unit includes a frequency agility function unit that changes the frequency of the transmission pulse according to a predetermined rule, and the compensation processing unit compensates the influence of the frequency change of the transmission pulse from the reception pulse. The inverse synthetic aperture radar according to claim 1, further comprising a frequency compensation processing unit that performs processing. 3. The ECCM function unit changes the pulse repetition frequency of a transmission pulse according to a predetermined rule.
The RF stagger function unit is provided, and the compensation processing unit is provided with a PRF compensation processing unit that performs compensation processing for eliminating the influence of the change in the pulse repetition frequency from the received pulse. Synthetic aperture radar. 4. An IS for eliminating the influence of the velocity component and the acceleration component of the target from the output signal of the compensation processing unit.
4. An AR processing unit, and an image generation unit that performs FFT processing on the output signal of the ISAR processing unit to generate an image of the target object. Reverse synthetic aperture radar. 5. A method for producing an inverse synthetic aperture radar image, which produces an image of a target object based on a series of received pulses, wherein the characteristics of the transmitted pulse are changed according to a predetermined rule.
By performing a CM step and a compensation process in consideration of the predetermined rule,
A method of generating an inverse synthetic aperture radar image, comprising: a compensation processing step of converting a series of received pulses into pulses having the constant characteristic. 6. The ECCM step includes a frequency agility step of changing a frequency of a transmission pulse according to a predetermined rule, and the compensation processing step includes a compensation processing of eliminating an influence of a frequency change of the transmission pulse from a reception pulse. The method for generating an inverse synthetic aperture radar image according to claim 5, further comprising a frequency compensation processing step to be performed. 7. The ECCM step includes a PRF stagger step of changing a pulse repetition frequency of a transmission pulse according to a predetermined rule, and the compensation processing step includes compensation for eliminating an influence of a change of the pulse repetition frequency from a reception pulse. P to process
6. An RF compensation processing step is included.
Alternatively, the method of generating the inverse synthetic aperture radar image according to the item 6. 8. An ISAR processing step for eliminating the influence of the velocity component and acceleration component of the target from the output signal obtained by the compensation processing step, and an FFT for the output signal obtained in the ISAR processing step.
An image generating step of performing processing to generate an image of the target, further comprising: a method for generating an inverse synthetic aperture radar image according to any one of claims 5 to 7.