JP2001141821A - Radar signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a conventional radar signal processor in a reverse synthetic aperture radar imaging the shape of a target that the Doppler frequency of a signal received from a target becomes very low when the rotational motion of the target is very slow because a target rotational speed can not be detected and a cross range resolution sufficient for recognizing the shape of the target can not be attained. SOLUTION: A maximum frequency calculator 21 is provided in order to determine the spread of Doppler frequency from the Doppler history of a target detected by means of a Doppler tracking unit 13 and a synthetic aperture time calculator 22 is provided in order to determine an optimal synthetic aperture time based on the Doppler frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar signal processor in an inverse synthetic aperture radar for imaging the shape of a target by utilizing the Doppler frequency generated by the rotational movement of the target.

[0002]

2. Description of the Related Art FIG. 10 shows a radar apparatus in which a conventional radar signal processor is incorporated as a part of components.
In the figure, 1 is a transmitter for generating a transmission pulse signal subjected to frequency modulation at a constant pulse repetition cycle, 2 is a transmission / reception switch for switching a transmission / reception circuit, 3 is a transmission pulse signal directed to a target and radiated. A transmission / reception antenna 4 for receiving a reflected signal from an object, and a reception 4 for amplifying and phase-detecting a reception signal input via a transmission / reception switch 2 with reference to a reference signal output from a transmitter 1 to obtain a video signal. And 5, a conventional radar signal processor, and 6 a display for displaying image data output from the radar signal processor 5. In the radar signal processor 5, reference numeral 7 denotes a range compressor for pulse-compressing the video signal using phase information subjected to frequency modulation by the transmitter 1. Reference numeral 8 denotes a two-dimensional video signal in a cross range direction × range direction. , A distance tracking processor 9 for estimating the speed data of the target, 10 a distance calculator for calculating the distance of the target for each pulse in order to estimate the speed data of the target, 11 a target A speed calculator for performing a smoothing process for smoothing a change in the distance of the target, and estimating the speed of the target; a range migration correction processor for correcting a change in the distance of the target moving with the movement of the target; A Doppler tracking processor for estimating the velocity data of the target; a phase compensation processor for compensating for the offset component and the primary component of the Doppler frequency generated with the movement of the target; The target is a cross-range compressor to compress the cross-range direction.

Next, the operation will be described. The transmitter 1
A transmission pulse signal that has been subjected to frequency modulation at a constant pulse repetition cycle is generated, and the antenna 3
Output to Further, the transmitter 1 outputs a reference signal used for phase detection and timing adjustment performed by the receiver 4 to the receiver 4. The transmission / reception antenna 3 radiates the input transmission pulse signal to the target and inputs it again as a reflected signal.
The receiver 4 inputs the reflection signal via the transmission / reception switch 2, amplifies and detects the phase using the reference signal output from the transmitter 1, converts the amplified signal into a video signal, and converts the amplified signal into a video signal. Output to

[0004] The radar signal processor 5 receives the video signal and obtains image data based on the principle of inverse synthetic aperture radar. Here, the basic principle of the inverse synthetic aperture radar will be described. Image data is represented by a two-dimensional image of the target in the range direction and cross-range direction.The target is compressed in the range direction using pulse compression technology, and the difference in Doppler frequency components generated by the movement of the target is focused on. To compress in the cross range direction. However, since the inverse synthetic aperture radar uses the motion of the target, it is necessary to correct an error factor that causes the video signal to move to a different range bin. Furthermore, it is necessary to remove the offset component and the primary component of the frequency which cause image degradation from the generated Doppler frequency. Therefore, in order to obtain a good target image, the distance tracking processor 9 and the range migration correction processor 12 correct the movement of the range bin with respect to these error factors, and the Doppler tracking processor 13 and the The phase compensation processor 14 removes the frequency offset component and the primary component. Hereinafter, these correction processes performed by the signal processor will be mainly described.

[0005] A video signal output from the receiver 4 is input to a range compressor 7, and refers to phase information subjected to frequency modulation by the transmitter 1 to match a video signal which is generally used in the field of radar signal processing. Pulse compression is performed by a filter method or the like. Next, this pulse-compressed signal will be described with reference to FIG. FIG. 11 shows video signals stored in the memory 8 in the cross range direction × range direction,
(A) shows the state before the processing by the range migration correction processor 12, and (b) shows the state after the processing. The pulse-compressed video signal is temporarily stored in the memory 8 in the cross-range direction × range direction, and is spread to a plurality of range bins because the range compressor 7 increases the resolution. Here, assuming that the target makes a linear motion approaching the radar, this video signal moves to a different range bin due to the motion of the target as shown in FIG. Therefore, it is necessary to correct the values so that they exist in the same range bin (FIG. 11).
(B)). Therefore, the range migration corrector 12 calculates a change in the target distance for each pulse (hereinafter referred to as a range migration correction amount) based on the information of the speed data detected by the distance tracking processor 9 and moves the range bin. .

[0006] The distance tracking processor 9 outputs speed data to the range migration correction processor 12.
2, a method of estimating the speed data will be described. FIG.
Reference numeral 2 denotes a range-compressed video signal received by the radar apparatus with a target having a plurality of scattering points (four points A to D in the figure), and shows a change in distance of the scattering points with respect to the pulse. . First, the distance calculator 10 detects a range bin having the largest reflected power from video signals spread over a plurality of range bins, and calculates the distance. By performing this processing for each pulse, a change in the distance to the target is acquired and output to the speed calculator 11. This distance information does not change stably due to scattering of a plurality of reflection points as shown in FIG. Therefore, the speed calculator 11 estimates the speed by performing smoothing using a process such as a least square method or a Kalman filter.

Next, a method of removing the offset component and the primary component of the Doppler frequency, which causes deterioration of the performance of the image data, will be described below with reference to FIG. FIG. 13 shows two-dimensional data in the cross range direction × range direction,
(A) shows the data processed by the range migration correction processor 12, and (b) shows the Doppler tracking processor 1.
3 shows the data after processing. First, the Doppler tracking processor 13 cuts out a range bin video signal which is the maximum point of the reflected power obtained by the distance calculator 10 from the video signal output from the range migration correction processor 12 (see FIG. 13A). ). Then, this video signal is subjected to FFT at certain time intervals to calculate a Doppler frequency (see FIG. 13B). By performing this processing while shifting in the time direction, the Doppler history of the target is calculated, and velocity data for each pulse of the target is estimated.

Next, the phase compensation processor 14 calculates the amount of phase compensation for each pulse using the velocity data, and performs complex multiplication with the signal output from the range migration correction processor 12 to perform phase compensation processing. I do. Then, the cross-range compressor 15 receives the signal after the phase compensation processing and compresses the signal in the cross-range direction by FFT in the pulse direction. From the principle of the inverse synthetic aperture radar, the resolution of this cross-range compression can be expressed by Equation 1. Where Δr is the cross-range resolution, θ is the angle at which the target has rotated in the data collection time, the so-called synthetic aperture time,
λ is the wavelength of the transmission wave.

[0009]

(Equation 1)

From equation (1), the cross range resolution is proportional to the angle of rotation of the target within the synthetic aperture time. If the rotation angle of the target is large within a certain synthetic aperture time, the cross range resolution increases and the rotation angle decreases. If it is small, the cross range resolution will be degraded. When the target rotates by a rotation angle required for the desired cross-range resolution, a high rotation speed requires a short synthetic aperture time, but a low rotation speed requires a long synthetic aperture time. For example, λ =
When 0.03 m and the target rotation speed = 0.015 rad / s, and when it is desired to obtain a cross range resolution of 1 m, the synthetic aperture time of 1 second is sufficient, but the target rotation speed = 0.001
At rad / s, a synthetic aperture time of 15 seconds is required.

As described above, the conventional radar signal processor compresses a target object in the range direction by the range compressor 7 and compresses the target object in the cross range direction by the cross range compressor 15 to convert two-dimensional image data. Obtainable. Further, the displacement of the range bin causing the image degradation is corrected by the distance tracking processor 9 and the range migration correction processor 1.
2, and the offset component and the primary component of the Doppler frequency are removed by the Doppler tracking processor 13 and the phase compensation processor 14, so that good image data can be obtained.

[0012]

In the conventional radar signal processor as described above, the cross range compression is performed by focusing on the Doppler frequency component generated by the movement of the target. However, since the target rotational speed cannot be detected, there is a problem that the synthetic aperture time for obtaining a sufficient cross-range resolution cannot be determined.

A radar signal processor according to the present invention has been made in order to solve such a problem, and has as its object to obtain a radar signal processor that estimates a target rotation speed and calculates an optimum synthetic aperture time. I do.

[0014]

SUMMARY OF THE INVENTION A radar signal processor according to a first aspect of the present invention utilizes a Doppler frequency generated by a rotational movement of a target object to image a shape of the target object in a reverse synthetic aperture radar. In the processor, a range compressor for pulse-compressing a video signal output from the receiver using a transmission signal subjected to frequency modulation by the transmitter, and a signal in the range direction (toward the target) A memory that stores two-dimensional data in a distance direction) × a cross range direction (a direction orthogonal to the range direction, a pulse direction), and a distance that calculates a distance of a maximum point of a reflected power of a target from a signal read from the memory. A calculator, a speed calculator for estimating speed data of a target from the distance of the maximum point, and calculating a range migration correction amount from the speed data A range migration correction processor for reading and correcting a signal for a time corresponding to the target motion from the memory, and shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing while shifting the time. FFT (Fast Fouri
e Transform) and a reference point having a maximum amplitude value from a frequency spectrum signal output from the section FFT calculator, and a history of a time change of the Doppler frequency at the reference point (hereinafter referred to as Doppler history) , A phase compensation speed calculator for estimating speed information of a target object from the Doppler history, and a phase compensation amount calculated from speed data output from the phase compensation speed calculator, A phase compensation processor that compensates for the signal after the range migration correction, a cross-range compressor that compresses a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, From the Doppler history output from the Doppler history detector, A least-squares line calculator for calculating a least-square line of the plastic frequency, a maximum frequency detector for detecting a difference between the above-mentioned Doppler history at each time from the least-square line of the Doppler frequency, and detection by the maximum frequency detector And a synthetic aperture time calculator that calculates the synthetic aperture time based on the difference obtained.

A radar signal processor according to a second invention is a maximum frequency detector for detecting a maximum value of a difference between the least square line obtained by the least square line calculator and the Doppler history at each time. And a synthetic aperture time calculator for calculating the synthetic aperture time from the maximum value detected by the maximum frequency detector.

A radar signal processor according to a third aspect of the present invention is a radar signal processor in an inverse synthetic aperture radar for imaging a shape of a target by utilizing a Doppler frequency generated by a rotational movement of the target. A range compressor that performs pulse compression processing on a video signal output from a receiver using a transmission signal that has been frequency-modulated by a transmitter, and converts the signal after the range compression into a range direction (distance direction toward a target) × A memory that stores two-dimensional data in a cross-range direction (a direction orthogonal to the range direction, a pulse direction), a distance calculator that calculates a distance of a maximum point of reflected power of the target from a signal read from the memory, A speed calculator for estimating speed data of the target from the distance of the maximum point, and calculating a range migration correction amount from the speed data; And a range migration correction processor for reading and correcting a signal for a time corresponding to the target movement from the signal, and a FFT (FFT) while shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing. Fast Fourier Tra
nsform) sectioned FFT calculator and this sectioned FF
A reference point having a maximum amplitude value is detected from the frequency spectrum signal output from the T calculator, and a history of the time change of the Doppler frequency at this reference point (hereinafter, Doppler history).
, A phase compensation speed calculator for estimating speed information of a target object from the Doppler history, and a phase compensation amount calculated from speed data output from the phase compensation speed calculator, A phase compensation processor that compensates for the signal after the range migration correction, a cross-range compressor that compresses a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, From the amplitude value of the Doppler history output from the Doppler history detector,
A maximum-minimum-average calculator for calculating the average value of the upper plural points and the average value of the lower plural points, and an average for calculating and outputting half of the difference between the upper average value and the lower average value. And a synthetic aperture time calculator for calculating a synthetic aperture time from the output of the averaged frequency detector.

Furthermore, a radar signal processor according to a fourth aspect of the present invention is a radar signal processor in an inverse synthetic aperture radar for imaging a shape of a target object by utilizing a Doppler frequency generated by a rotational movement of the target object. A range compressor for pulse-compressing a video signal output from a receiver using a transmission signal subjected to frequency modulation by a transmitter, and a signal in a range direction (distance direction toward a target) after the range compression. A memory for storing as two-dimensional data in a cross range direction (a direction orthogonal to the range direction, a pulse direction), and a distance calculator for calculating a distance of a maximum point of reflected power of the target from a signal read from the memory. A speed calculator for estimating speed data of the target from the distance of the maximum point, and calculating a range migration correction amount from the speed data; A range migration correction processor for reading and correcting a signal for a time corresponding to the target motion from the memory; and a FFT while shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing. (Fast Fourie
Transform) and a reference point having the maximum amplitude value from the frequency spectrum signal output from the section FFT calculator, and the time change history (hereinafter referred to as Doppler history) of the Doppler frequency at this reference point is detected. Calculating a Doppler history detector, a phase compensation speed calculator for estimating speed information of the target from the Doppler history, and calculating a phase compensation amount from speed data output from the phase compensation speed calculator. A phase compensation processor for compensating the signal after the range migration correction, a cross-range compressor for compressing a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, From the Doppler history amplitude value output from the Doppler history detector, A median value, a maximum-minimum-median value calculator for calculating the median value of a plurality of lower-order points, and an averaging frequency detector for calculating and outputting half of the difference between the median value on the upper side and the median value on the lower side. And a synthetic aperture time calculator for calculating the synthetic aperture time from the output of the averaging frequency detector.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing the first embodiment of the present invention, and in particular, is a diagram showing a configuration of a radar signal processor 5. Note that the same components as those in the related art are denoted by the same reference numerals, and description thereof will be omitted. Further, although the processing content of the Doppler tracking processor 13 is the same as that of the conventional technology, a detailed description of each process has been added for the sake of convenience that information used during processing is different from that of the conventional technology. In the figure, reference numeral 16 denotes a video signal output from the range migration correction processor 12 which is obtained by cutting out data at a fixed time interval while shifting the time, and performing FFT.
(Fast Fourier Transform), a segmented FFT calculator, 17 detects a reference point, which is the maximum amplitude point, from the frequency spectrum output from the segmented FFT calculator 16, and records a time change history (hereinafter, Doppler history) of the Doppler frequency. Doppler history detector to calculate,
Reference numeral 18 denotes a phase compensation speed calculator for estimating the phase compensation speed from the Doppler history, 19 denotes a motion analysis processor constituted by a later-described least square line calculator 20 and a later-described maximum frequency detector 21, and 20 denotes a motion analysis processor. A least-squares line calculator 21 for calculating the least-square line of the Doppler frequency with respect to the time axis of the history from the above-mentioned Doppler history. The maximum frequency detector 22 for calculating the maximum difference between the two is a synthetic aperture time calculator that calculates the optimal synthetic aperture time for the target motion based on the Doppler frequency output from the motion analysis processor 19. Hereinafter, the Doppler tracking processor 13, the motion analysis processor 19, and the synthetic aperture time calculator 22 will be described.

First, the Doppler tracking processor 13 will be described. Doppler tracking processor 13 is a segmented FFT calculator 1
6, a Doppler history detector 17 and a phase compensation speed calculator 18. The segmented FFT calculator 16 inputs a video signal from the range migration correction processor 12, and this signal is obtained by cutting out the range bin detected as the maximum amplitude value by the distance calculator 10.
FIG. 13B shows a conceptual diagram of the processing of the partitioned FFT, and shows the video signal after the partitioned FFT in two dimensions of frequency spectrum × cross range. From the figure, the segmented FFT calculator 16 cuts out the video signal while shifting it in the cross-range direction and performs FFT,
A time-varying frequency spectrum is calculated. These spectral data are output to the Doppler history detector 17. After inputting this spectrum data, the Doppler history detector 17 detects the Doppler history by detecting the maximum amplitude at each time and extracting the Doppler frequency. The phase-compensating speed calculator 18 calculates the speed from this Doppler history according to equation (2). Here, Fd is the Doppler frequency. This speed is output to the phase compensation processor 14.

[0020]

(Equation 2)

Next, the motion analysis processor 19 will be described. The motion analysis processor 19 includes a least-squares straight line calculator 20 and a maximum frequency detector 21, and analyzes the motion of the target based on the Doppler history output from the Doppler history detector 17. As shown in FIG. 2, the motion of the target is divided into a translational component motion and a rotational component motion. Since the motion of the translation component is the acceleration motion of the target, the speed changes temporarily. If the radar is mounted on a moving platform such as an airplane, the radar has a drift component added to the translation component because the radar captures the target speed as a relative speed. In any case, since the Doppler frequency generated by the speed of the translation component is proportional to the speed, FIG.
It changes as shown in In addition, the motion of the rotational component is mainly governed by pitch motion and roll motion in a ship as an example, and becomes a sine wave motion. Therefore, the Doppler frequency of the rotation component changes as shown in FIG. As shown in FIG. 3C, the Doppler frequency obtained by synthesizing these motions is obtained by adding a long-period drift component to the sinusoidal motion.

Therefore, the least squares straight line calculator 20 estimates the motion of the target translation component by calculating the change of the drift component using the Doppler history output from the Doppler history detector 17. The motion of the translation component of the target is estimated by calculating a least-squares straight line with respect to the time axis of the Doppler history (see FIG. 4). The estimated value of the Doppler frequency is output to the maximum frequency detector 21.

The maximum frequency detector 21 estimates the rotational motion of the target using the estimated Doppler frequency output from the least squares straight line calculator 20 and the Doppler history output from the Doppler history detector 17. The estimation of the target rotational movement is performed by calculating the difference between the Doppler frequency at each time and the estimated value of the Doppler frequency, whereby the amplitude value of the target sinusoidally changing Doppler history can be obtained (FIG. 4). The maximum value of the difference between the amplitudes is the maximum value of the Doppler frequency at which the target spreads in the Doppler direction, that is, the Doppler frequency at the moment when the radar has the maximum speed. At this time, an image can be formed with the maximum resolution by the inverse synthetic aperture radar, and the best image can be obtained by setting the synthetic aperture time according to the spread. The maximum value of the difference between the Doppler frequencies is output to the synthetic aperture time calculator 22.

Next, the synthetic aperture time calculator 22 will be described. Inverse synthetic aperture radar focuses on the Doppler frequency generated by the movement of a target object to achieve higher resolution. To improve cross-range resolution, it is necessary to set the optimal synthetic aperture time for changes in Doppler frequency. .
The frequency bin width is expressed by Expression 3 using the synthetic aperture time. Here, Δf is the frequency bin width, and T is the synthetic aperture time.

[0025]

(Equation 3)

On the other hand, when the spread of the Doppler frequency is ΔF, if the number of pixels of the target in the case of forming an image is desired to be N, the frequency bin width is expressed by the following equation (4). Thus, the synthetic aperture time is shown as in Equation 5.

[0027]

(Equation 4)

[0028]

(Equation 5)

As described above, the synthetic aperture time calculator 22 calculates the optimum synthetic aperture time from the spread of the Doppler frequency output from the maximum frequency detector 21 and the desired number of pixels of the target object according to the equation (5). The data is output to the memory 8 as the time of the video signal processed by the correction processor 12 (the number of data in the cross range direction). If a video signal corresponding to this time is read out and processed by the inverse synthetic aperture radar, an image of a target having a desired number of pixels can be obtained. FIG. 5 shows a conceptual diagram of the above processing. Also, as an example, when the target is rotating and the Doppler spread is 10 Hz, if the desired number of pixels is required to be 20 pixels, the synthetic aperture time of 2 seconds is optimal. Only translational motion without rotating motion,
When the Doppler spread is 1 Hz, the synthetic aperture time is 20
Seconds.

Embodiment 2 FIG. FIG. 6 is a configuration diagram showing a second embodiment of the present invention. Note that the same components as those in the related art are denoted by the same reference numerals, and description thereof will be omitted. In the figure, reference numeral 23 denotes a maximum-minimum-average calculator for calculating the average value of the upper plural points of the Doppler history and the average value of the lower plural points, respectively. This is an averaging frequency calculator that calculates half of the difference between the average value on the side and the average value on the lower side.

Next, the operation will be described. Embodiment 1
In order to analyze the Doppler history of the target, the least-squares straight line was found.However, the Doppler history is usually a huge one with more than several thousand data points, so the process of finding the least-square straight line is also required. It takes time. Therefore, the maximum-minimum-average value calculator 23 estimates the target motion using only a part of the Doppler history data. The estimation of the target motion is performed by detecting data of the upper multiple points and data of the lower multiple points of the Doppler history,
Calculate the average of each. Since the number of data points contributes to a reduction in processing time, the number of data points is set to a value of about several tenths to one hundredth tenths of the total number of data of Doppler history. Motion estimation is performed by averaging using multiple data, so even if impulse-like noise is superimposed on Doppler history and it is detected as the maximum or minimum value, the error can be reduced. (See FIG. 7A). The upper and lower average values of the Doppler frequency are output to the averaging frequency calculator 24.

The averaging frequency calculator 24 calculates the maximum and minimum
The offset component is removed from the upper and lower Doppler frequency average values calculated by the average value calculator 23 to extract the Doppler frequency of the rotational motion of the target. As a method, half of the difference between the average value on the maximum side and the average value on the minimum value side is calculated. By this processing, the offset component of the target object can be removed, and only the Doppler frequency of the rotational motion can be extracted (see FIG. 7B). The Doppler frequency is output to the synthesis time calculator 22.

Embodiment 3 FIG. 8 is a configuration diagram showing a third embodiment of the present invention. Note that the same components as those in the related art are denoted by the same reference numerals, and description thereof will be omitted. In the figure, reference numeral 25 denotes a maximum / minimum-median calculator for calculating the median of the data of the upper plurality of points of the Doppler history and the median of the data of the lower plurality of points, respectively. This is an averaging frequency calculator that calculates half of the difference between the median value on the upper side and the median value on the lower side.

Next, the operation will be described. Embodiment 2
In order to analyze the Doppler history of the target, a plurality of upper and lower average values were obtained, and it was possible to cope with impulse-like noise, but this impulse-like noise was converted to a normal signal. If it is extremely large,
The error from the desired average value increases. Further, even when the impulse-shaped noise is small, an error occurs to some extent. Therefore, the maximum / minimum-median calculator 25 calculates the median instead of the average. Therefore, in estimating the target motion, the data of the upper plurality of points and the data of the lower plurality of points of the Doppler history are detected, and the respective median values are calculated.
Since the number of data points contributes to a reduction in processing time, the number of data points is set to a value of about several tenths to one hundredth tenths of the total number of data of Doppler history. Since the median value is calculated using multiple data for motion estimation, impulse-like noise is superimposed on Doppler history, and even if it is detected as the maximum or minimum value, the error is reduced. (See FIG. 9A). The average value of the Doppler frequency is output to the averaging frequency calculator 26.

The averaging frequency calculator 26 calculates the maximum and minimum
The offset component is removed from the upper and lower Doppler frequency average values calculated by the median value calculator 25, and the Doppler frequency of the rotational motion of the target is extracted. As a method, half of the difference between the median value on the upper side and the median value on the lower side is calculated.
By this process, the offset component of the target is removed,
Only the Doppler frequency of the rotational motion can be extracted (see FIG. 9B). The Doppler frequency is output to the synthesis time calculator 22.

[0036]

According to the first and second aspects of the invention, since the least square line calculator and the maximum frequency detector are provided, the motion of the target is analyzed from the Doppler history of the target, and the spread of the Doppler frequency is reduced. The calculation and the provision of the synthetic aperture time calculator have an effect that the optimum synthetic aperture time can be calculated from the Doppler frequency.

According to the third aspect of the present invention, a maximum-minimum-average value calculator and an averaging frequency calculator are provided.
After analyzing the motion of the target from the Doppler history of the target with a small amount of calculation, the spread of the Doppler frequency can be calculated, and the optimal synthetic aperture time can be calculated from the Doppler frequency by using the synthetic aperture time calculator. Can be calculated.

According to the fourth aspect of the present invention, by providing the maximum / minimum-median value calculator and the averaging frequency calculator,
Even when the impulse-like unnecessary noise is superimposed, the spread of the Doppler frequency can be calculated after analyzing the motion of the target from the Doppler history of the target, and the Doppler frequency can be calculated by providing the synthetic aperture time calculator. There is an effect that the optimum synthetic aperture time can be calculated from the frequency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a radar signal processor according to the present invention;

FIG. 2 is a diagram for explaining a motion component of a target in the first embodiment of the radar signal processor according to the present invention;

FIG. 3 is a diagram for explaining Doppler history in the first embodiment of the radar signal processor according to the present invention;

FIG. 4 is a diagram for explaining a calculation method of a motion analysis process in the first embodiment of the radar signal processor according to the present invention;

FIG. 5 is a diagram for explaining a method of calculating a synthetic aperture time in the first embodiment of the radar signal processor according to the present invention;

FIG. 6 is a diagram showing a second embodiment of the radar signal processor according to the present invention;

FIG. 7 is a diagram for explaining a maximum-minimum-average calculator in a second embodiment of the radar signal processor according to the present invention;

FIG. 8 is a diagram illustrating a third embodiment of the radar signal processor according to the present invention;

FIG. 9 is a diagram for explaining a maximum-minimum-median value calculator in a radar signal processor according to Embodiment 3 of the present invention;

FIG. 10 is a diagram showing a conventional radar device.

FIG. 11 is a diagram for explaining a processing method of a reference point detector in a conventional radar signal processor.

FIG. 12 is a diagram for explaining a range-compressed video signal and a distance tracking processor in the radar signal processor according to the first embodiment of the present invention.

FIG. 13 is a diagram for explaining a partitioned FFT process in the first embodiment of the radar signal processor according to the present invention;

[Explanation of symbols]

1 transmitter, 2 transmission / reception switch, 3 transmission / reception antenna, 4
Receiver, 5 signal processor, 6 display, 7 range compressor, 8 memory, 9 distance tracking processor, 10 distance calculator, 11 speed calculator, 12 range migration correction processor, 13 Doppler tracking processor, 14 Phase compensation processor, 15 cross-range compressor, 16-section FF
T calculator, 17 Doppler history detector, 18 phase compensation calculator, 19 motion analysis processor, 20 least square line calculator, 21 maximum frequency detector, 22 synthetic aperture time calculator, 23 maximum minimum-average value calculation 24 averaged frequency calculator 25 maximum / minimum-median calculator 2
6 Average frequency calculator.

Claims (4)

[Claims] 1. A radar signal processor in an inverse synthetic aperture radar for imaging the shape of a target using the Doppler frequency generated by the rotational movement of the target, the transmission signal being frequency-modulated by a transmitter. A range compressor for pulse-compressing a video signal output from a receiver, and converting the signal after range compression into a range direction (distance direction toward a target) x a cross range direction (a direction orthogonal to the range direction; A memory for storing two-dimensional data (pulse direction), a distance calculator for calculating the distance of the maximum point of the reflected power of the target from the signal read from the memory, and speed data of the target from the distance of the maximum point And a range migration correction amount is calculated from the speed data, and a signal for a time corresponding to the target motion is read from the memory. And range migration correction processing unit for correcting, FFT while shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing time (Fast Four
ie Transform), a piecewise FFT calculator,
A Doppler history detector for detecting a reference point having a maximum amplitude value from the frequency spectrum signal output from the partitioned FFT calculator, and calculating a time change history (hereinafter referred to as Doppler history) of the Doppler frequency at the reference point; A phase compensating speed calculator for estimating speed information of a target from Doppler history, and a phase compensation amount is calculated from speed data output from the phase compensating speed calculator to compensate for the signal after the range migration correction. A phase compensation processor, a cross-range compressor for compressing a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, and a Doppler output from the Doppler history detector. A least-squares line that calculates the least-square line of Doppler frequency with respect to the time axis from history And a maximum frequency detector for detecting a difference between the Doppler history at each time from the least square line of the Doppler frequency, and a synthetic aperture time is calculated based on the difference detected by the maximum frequency detector. A radar signal processor including a synthetic aperture time calculator. 2. A maximum frequency detector that detects a maximum value of a difference between the least square line obtained by the least square line calculator and the Doppler history at each time, and a maximum frequency detector that detects the maximum value. The radar signal processor according to claim 1, further comprising: a synthetic aperture time calculator that calculates a synthetic aperture time from a maximum value. 3. A radar signal processor in an inverse synthetic aperture radar for imaging a shape of a target object by utilizing a Doppler frequency generated by a rotational movement of the target object. A range compressor for pulse-compressing a video signal output from a receiver, and converting the signal after range compression into a range direction (distance direction toward a target) x a cross range direction (a direction orthogonal to the range direction; A memory for storing two-dimensional data (pulse direction), a distance calculator for calculating the distance of the maximum point of the reflected power of the target from the signal read from the memory, and speed data of the target from the distance of the maximum point And a range migration correction amount is calculated from the speed data, and a signal for a time corresponding to the target motion is read from the memory. And range migration correction processing unit for correcting, FFT while shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing time (Fast Four
ie Transform), a piecewise FFT calculator,
A Doppler history detector for detecting a reference point having a maximum amplitude value from the frequency spectrum signal output from the partitioned FFT calculator, and calculating a time change history (hereinafter referred to as Doppler history) of the Doppler frequency at the reference point; A phase compensating speed calculator for estimating speed information of a target from Doppler history, and a phase compensation amount is calculated from speed data output from the phase compensating speed calculator to compensate for the signal after the range migration correction. A phase compensation processor, a cross-range compressor for compressing a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, and a Doppler output from the Doppler history detector. Calculate the average value of upper multiple points and the average value of lower multiple points, respectively, from the amplitude value of history A maximum-minimum-average value calculator, an averaged frequency detector that calculates and outputs a half of the difference between the upper average value and the lower average value, and a synthetic aperture based on the output of the averaged frequency detector. A radar signal processor comprising a synthetic aperture time calculator for calculating time. 4. A radar signal processor in an inverse synthetic aperture radar for imaging a shape of a target object by utilizing a Doppler frequency generated by a rotational movement of the target object. A range compressor for pulse-compressing a video signal output from a receiver, and converting the signal after range compression into a range direction (distance direction toward a target) x a cross range direction (a direction orthogonal to the range direction; A memory for storing two-dimensional data (pulse direction), a distance calculator for calculating the distance of the maximum point of the reflected power of the target from the signal read from the memory, and speed data of the target from the distance of the maximum point And a range migration correction amount is calculated from the speed data, and a signal for a time corresponding to the target motion is read from the memory. And range migration correction processing unit for correcting, FFT while shifting the maximum point of the reflected power detected by the distance calculator from the signal after the range migration correction processing time (Fast Four
ie Transform), a piecewise FFT calculator,
A Doppler history detector for detecting a reference point having a maximum amplitude value from the frequency spectrum signal output from the partitioned FFT calculator, and calculating a time change history (hereinafter referred to as Doppler history) of the Doppler frequency at the reference point; A phase compensating speed calculator for estimating speed information of a target from Doppler history, and a phase compensation amount is calculated from speed data output from the phase compensating speed calculator to compensate for the signal after the range migration correction. A phase compensation processor, a cross-range compressor for compressing a target in the cross-range direction by FFT of a signal output from the phase compensation processor in the cross-range direction, and a Doppler output from the Doppler history detector. Calculate the median value of upper multiple points and the median value of lower multiple points, respectively, from the amplitude value of history A maximum-minimum-median value calculator, an averaged frequency detector for calculating and outputting half of the difference between the upper median value and the lower median value, and a synthetic aperture based on the output of the averaged frequency detector. A radar signal processor comprising a synthetic aperture time calculator for calculating time.