JP2001289947A - Inverse synthetic aperture radar and method of forming inverse synthetic aperture radar image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly obtain the ISAR image of a target in a disturbance radio wave transmitting environment in an ISAR using the ECCM function. SOLUTION: The ISAR for forming an image of the target on the basis of a series of received pulses is constituted. An ECCM function part 14 is arranged for changing a characteristic of a transmitting pulse according to a prescribed rule. A compensating processing part 16 is arranged for converting the series of received pulses into pluses having the constant characteristic by performing compensating processing taking the prescribed rule into consideration. The ISAR image is formed on the basis of an output signal of the compensating processing part 16 by a well-known technique.

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 for generating an inverse synthetic aperture radar image (ISAR image).
M function) and a method of generating an inverse synthetic aperture radar image.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional inverse synthetic aperture radar (IS).
FIG. 3 is a conceptual diagram for explaining the operation of AR). In FIG. 5, a target 1 is an object to be subjected to the ISAR processing, and a 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 shown by an arrow Y1. Also,
After being reflected by the target 1, the radar 2 receives a returning radio wave as indicated by an arrow Y2 for a certain period of time, and performs an ISAR process on the received signal to obtain an ISAR image of the target 1.

FIG. 6 is a block diagram of an ISAR processing unit included in the radar 2. As shown in FIG.
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. Speed component compensator 3
The acceleration component compensating unit 4 performs processing described later on the input signal and outputs the processed signal. The radar 2 generates an ISAR image based on the signal output from the acceleration component compensator 4.

FIG. 7A shows an example of a trajectory of the distance between the target 1 and the radar 2 which is directly detected from the reception signal of the radar 2 when the target 1 has a velocity component. FIG.
As shown in (A), when the target 1 has a velocity component, the distance between the target 1 and the radar 2 changes over time. That is, when the target 1 has a velocity component, the radar 2 receives a signal reflecting the velocity component.

[0005] In order to obtain an ISAR image, it is necessary that the influence of the velocity component of the target 1 be eliminated from the signal on which it is based. The above-mentioned velocity component compensator 3 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-mentioned requirement. That is, the velocity component compensator 3 performs compensation processing on the input signal such that the relative distance between the target 1 and the radar 2 is constant as shown in FIG.

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

[0007] In order to obtain an ISAR image, it is necessary that the influence of the acceleration component of the target 1 be eliminated from the signal on which it is based. The above-described acceleration component compensating unit 4 performs a compensation process for eliminating the influence of the acceleration component of the target 1 from the speed compensating signal output from the speed component compensating unit 3 in order to meet the above demand. That is, the acceleration component compensator 4
The compensation processing is performed on the velocity compensation signal so that the Doppler frequency superimposed on the signal output from the acceleration component compensator 4 becomes constant as shown in FIG. Hereinafter, the signal output from the acceleration component supplementary part 4 is referred to as a “speed / acceleration compensation signal”.

From the speed / 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 speed / acceleration compensation signal is the same as a signal obtained when the target 1 is stationary with respect to the radar 2, that is, a signal including only the fluctuation component of the target 1. The radar 2 performs an FFT process on the velocity / acceleration compensation signal to obtain an ISAR image representing a 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 radio waves transmitted from the radar 2 to generate jamming radio waves, that is, an electronic back search function (ECM function).
Some have. In the conventional ISAR, when the target 1 has the ECM function and the target 1 emits jamming radio waves, the ISAR image may not be generated properly.

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

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an ISAR capable of appropriately obtaining an ISAR image of a target object even in an environment where jamming radio waves are emitted. This is the first object. Also,
The present invention has been made in order to solve the above-described problems, and it is a first object of the present invention to provide a method for generating an ISAR image for properly obtaining an ISAR image of a target in an environment where jamming radio waves are emitted. The purpose of.

[0012]

According to the first aspect of the present invention,
An inverse synthetic aperture radar for generating an image of a target object based on a series of pulses received, an ECCM function unit for changing characteristics of a transmission pulse according to a predetermined rule, and performing a compensation process in consideration of the predetermined rule. According to the present invention, there is provided a compensation processing unit for converting a series of received pulses into a pulse having a constant characteristic.

According to a second aspect of the present invention, there is provided the inverse synthetic aperture radar according to the first aspect, wherein the ECCM function unit includes a frequency agility function unit that changes a frequency of a transmission pulse in accordance with a predetermined rule. The processing unit includes 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.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the inverse synthetic aperture radar according to the above, the ECCM function unit includes a PRF stagger function unit that changes a pulse repetition frequency of a transmission pulse in accordance with a predetermined rule, and the compensation processing unit calculates the pulse repetition frequency from a reception pulse. It is characterized by including a PRF compensation processing unit for performing compensation processing for eliminating the influence of the change.

According to a fourth aspect of the present invention, there is provided the inverse synthetic aperture radar according to any one of the first to third aspects, wherein a velocity component and an acceleration component of the target object are obtained from an output signal of the compensation processing unit. An ISAR processing unit for eliminating the influence,
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.

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

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

The invention according to claim 7 is the invention according to claim 5 or 6.
The method of generating an inverse synthetic aperture radar image as described above, wherein 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 the steps of: The present invention is characterized by including a PRF compensation processing step of performing compensation processing for eliminating the influence of a change in frequency.

According to an eighth aspect of the present invention, there is provided the method of generating an inverse synthetic aperture radar image according to any one of the fifth to seventh aspects, wherein the target object is obtained from an output signal obtained in the compensation processing step. Further comprising an ISAR processing step of eliminating the influence of the velocity component and acceleration component, and an image generating step of performing an FFT processing on the output signal obtained in the ISAR processing step to generate an image of the target. It is a feature.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.

Embodiment 1 FIG. 1 shows a principle diagram of the ISAR of the present invention. The ISAR shown in FIG. 1 includes an antenna 10 that emits a transmission pulse to a target and receives a reflected signal generated by the target. A circulator 12 is connected to the antenna 10. The circulator 12 supplies a transmission pulse generated in the ISAR transmission system to the antenna 10 and supplies a 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 function section
It has a function of changing the characteristics of the transmission pulse transmitted from the antenna 10 according to a predetermined rule. When the characteristics of the transmission pulse change in this way, the target object cannot easily analyze the characteristics of the transmission pulse emitted from the ISAR, even if the target has the ECM function. For this reason, according to the ISAR of the present embodiment, even when the target has the ECM function, it is possible to receive the reception pulse resulting from the transmission pulse emitted by itself without being confused with the jamming 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 includes a reception pulse resulting from a transmission pulse emitted from the ISAR.
The change of the characteristic resulting from the function of this is superimposed. ECCM
The compensation processing unit 16 is a unit for compensating for the above-described characteristic change superimposed on the received pulse. Therefore, in the blocks subsequent to the compensation processing unit 16, predetermined processing can be performed on the basis of pulses having constant characteristics.

The signal processed by the ECCM compensation processing unit 16 is supplied to an ISAR processing unit 18. The ISAR processing section 18 includes a velocity component compensating section 3 and an acceleration component compensating section 4 which are also mounted on a conventional ISAR (see FIG. 6). The speed 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 of the speed component and 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 unit 18,
Even when the target has a velocity component or 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 this embodiment generates an ISAR image by performing FFT processing on the signal obtained in this manner.

As described above, the ISAR of the present embodiment can accurately identify a received pulse caused by a transmission pulse generated by itself and properly perform the ISAR even in an environment where jamming radio waves exist.
Images can be generated. Therefore, I of the present embodiment
According to SAR, even when an ECM function is mounted on a target, an ISAR image of the target can be appropriately generated.

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

That is, the ISAR of the present embodiment is the one shown in FIG.
Is provided with a frequency agility function unit 20 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 a transmission pulse emitted toward a target according to a predetermined rule. On the other hand, the frequency compensation processing unit 22 performs compensation processing in consideration of a frequency change of each pulse received by the antenna 10, more specifically, a phase generated between reception pulses due to a frequency change of a transmission pulse. Execute a process for compensating for the change.

Hereinafter, the frequency agility function unit 20
A case where the following two types of frequencies are used alternately 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 the ISAR is R, the phase of the received pulse at the position of the antenna 10 is
For each of the frequency 1 (F1) and the frequency 2 (F2), it can be expressed as the following equation. Phase φ ₁ = 4πR / λ ₁ (3) Phase φ ₂ = 4πR / λ ₂ (4)

A phase φ ₁ corresponding to frequency 1 (F1),
From the above equations (3) and (4), the following equation is established between the phase ₂ and the phase 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 component of the reception pulse corresponding to the transmission pulse of frequency 1, and Q ₁ , which is the imaginary 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 a real component of a reception pulse corresponding to a transmission pulse of frequency 2, and Q ₂ , which is an imaginary component thereof. . φ ₂ = tan ^-1 (Q ₂ / I ₂ ) (7)

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

Here, assuming that I ₁ = I ₂ for convenience of explanation, Q ₁ = I ₂ · tan (λ ₂ / λ ₁ · tan ^-1 (Q ₂ / I ₂ )) (9) , the received signals I ₂ and Q ₂ in the frequency 2 can be converted to a received signal I ₁ and Q ₁ in the 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 Thus, I ₂ and Q
_A similar conversion can be achieved while preserving the phase of ₂ .

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

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

That is, the ISAR of this embodiment is the same as that 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 according to a predetermined rule. On the other hand, the PRF compensation processing unit 26
, A process of compensating for a change in the PRF of the received pulse received and converting the received pulse into a signal obtained when the PRF is constant.

A case where the PRF stagger function unit 24 alternately uses two types of PRFs for each pulse will be described below with reference to FIG. FIG. 4A shows the timing at which a transmission pulse is issued from the ISAR. Here, as shown in FIG. 4A, a pulse interval a and a pulse interval b are used corresponding to two types of PRF. FIG. 4B shows sampling points before and after the PRF compensation processing.

In the process of generating an ISAR image, FFT processing is performed on video data in the pulse direction. For this reason, the signal on which the processing is based includes a certain PRF
, That is, pulses generated at regular intervals must be included. For example, consider a constant sampling period that takes the maximum and minimum amplitudes for the waveform shown in FIG. 4 and 4 indicate sampling points corresponding to this sampling period. In order to generate an ISAR image, it is necessary that a pulse included in a signal on which the ISAR image is based corresponds to a sampling point indicated by ● or ▲.

As shown in FIG. 4A, when intervals a and b are alternately used as intervals between transmission pulses,
Corresponding to those pulses, ● and ○ 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 に into the sampling point ▲. In the present embodiment, the PRF compensation processing unit 26 measures a change in the amplitude of a signal received at a plurality of sampling points, and calculates the amplitude of the signal at the sampling point ▲ based on the measured value. Therefore, IS
In the blocks subsequent to the AR processing unit 18, an ISAR image can be appropriately generated based on a signal obtained at a fixed sampling period.

As described above, the ISAR of this embodiment can emit a transmission pulse using a plurality of PRFs.
For this reason, according to the ISAR of this embodiment, the target is E
Even in the case of having the CM function, it is possible to receive a reception pulse resulting from a transmission pulse emitted by itself without being confused with a jamming radio wave. In addition, the ISA of the present embodiment
R can convert the received pulse whose PRF changes in the PRF compensation processing unit 26 into a signal having a constant sampling cycle. For this reason, according to the ISAR of the present embodiment, even when an ECM function is mounted on a target, an ISAR image of the target can be appropriately generated.

[0043]

Since the present invention is configured as described above, it has the following effects. Claim 1
According to the invention described in the fifth aspect, the characteristics of the transmission pulse can be changed by using the ECCM function, and the change in the characteristics can be excluded from the received signal.
For this reason, according to the present invention, even in an environment where jamming radio waves are present, a reception pulse resulting from a transmission pulse emitted by itself is accurately captured, and an inverse synthetic aperture radar image is appropriately formed based on the reception pulse. Can be generated.

According to the second or sixth aspect of the present invention, E
The frequency agility function can be used as the CCM function. For this reason, according to the present invention, even in an environment where jamming radio waves are present, a reception pulse resulting from a transmission pulse emitted by itself is accurately captured, and an inverse synthetic aperture radar image is appropriately formed based on the reception pulse. Can be generated.

According to the third or seventh aspect of the present invention, E
The PRF stagger function can be used as the CCM function. For this reason, according to the present invention, even in an environment where jamming radio waves are present, a reception pulse resulting from a transmission pulse emitted by itself is accurately captured, and an inverse synthetic aperture radar image is appropriately formed based on the reception pulse. Can be generated.

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

[Brief description of the drawings]

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

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

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

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

FIG. 5 is a diagram illustrating a positional relationship between a target and an 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 speed component compensator provided in a conventional ISAR.

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

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

[Explanation of symbols]

3 speed component compensator, 4 acceleration component substation,
10 antennas, 12 circulators, 14
ECCM function section, 16 compensation processing section, 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.

Claims (8)

[Claims] 1. An inverse synthetic aperture radar for generating an image of a target object based on a series of received pulses, wherein the EC changes 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 a frequency of a transmission pulse according to a predetermined rule, and the compensation processing unit performs compensation for eliminating an influence of a frequency change of the transmission pulse from a reception pulse. The inverse synthetic aperture radar according to claim 1, further comprising a frequency compensation processing unit that performs a process. 3. The ECCM function unit changes a pulse repetition frequency of a transmission pulse according to a predetermined rule.
3. The reverse of claim 1, further comprising an RF stagger function unit, wherein the compensation processing unit includes a PRF compensation processing unit that performs a compensation process for eliminating an influence of a change in the pulse repetition frequency from a received pulse. 4. Synthetic aperture radar. 4. An IS for eliminating the influence of a velocity component and an acceleration component of the target from an output signal of the compensation processing unit.
4. The image processing apparatus according to claim 1, further comprising: an AR processing unit; and an image generation unit configured to generate an image of the target by performing FFT processing on an output signal of the ISAR processing unit. 5. Inverse synthetic aperture radar. 5. An inverse synthetic aperture radar image generation method for generating an image of a target object based on a series of received pulses, wherein the EC changes a characteristic of a transmission pulse according to a predetermined rule.
By performing a CM step and a compensation process in consideration of the predetermined rule,
A compensation processing step of converting a series of received pulses into pulses having the constant characteristics, a method of generating an inverse synthetic aperture radar image. 6. The ECCM step includes a frequency agility step of changing a frequency of a transmission pulse in accordance with a predetermined rule, and the compensation processing step includes performing a compensation process for eliminating an influence of a frequency change of the transmission pulse from a reception pulse. 6. The method according to claim 5, further comprising a frequency compensation processing step. 7. The ECCM step includes a PRF staggering step of changing a pulse repetition frequency of a transmission pulse according to a predetermined rule, and the compensation processing step includes a step of eliminating the influence of the change of the pulse repetition frequency from a reception pulse. P to process
6. The method according to claim 5, further comprising an RF compensation processing step.
Or a method for generating an inverse synthetic aperture radar image according to 6. 8. An ISAR processing step for eliminating an influence of a velocity component and an acceleration component of the target from an output signal obtained in the compensation processing step, and an FFT is performed on the output signal obtained in the ISAR processing step.
The method according to any one of claims 5 to 7, further comprising: an image generation step of performing processing to generate an image of the target object.