JP2018100886A - Rader system and radar signal processing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve at least either a range resolution or a Doppler resolution to high resolution, even when a frequency bandwidth is relatively narrow or an observation time is relatively short.SOLUTION: A rader system generates a range-Doppler image from a radar reception signal, extracts reflection points Nall from the range-Doppler image by an amplitude threshold, discriminates the extracted reflection points Nall per N(N≤Nall) group of adjacent points, arranges them on a range-Doppler axis (fast-slow-time axis) per group, applies expansion array processing to at least either a range axis (Nr point) or a doppler axis (Nd point) obtained by performing an inverse Fourier transformation on each of the range axis and the Doppler axis to have 2 Nr-1 point or 2 Nd-1 point, images again the axis to which the expansion array processing is applied by performing Fourier transformation and outputs a high resolution image by performing amplitude overlapping to an image result concerning the N point.SELECTED DRAWING: Figure 1

Description

  The present embodiment relates to a radar apparatus to which extended array processing is applied and a radar signal processing method thereof.

  Conventional radar devices are required to improve range resolution and Doppler resolution. In order to improve the range resolution, processing such as pulse compression with a wide transmission frequency band is effective, but a wider band is required. On the other hand, in order to improve the Doppler resolution, it is necessary to lengthen the observation time (increase the number of hits), but the search frame time decreases accordingly.

  For the above countermeasure, conventionally, an extended array process using a KR product array (see Non-Patent Document 1) or the like is applied. However, in the case of a radar target, since there is a correlation between reflection points, a false target may occur due to the execution of the extended array process.

KR product array, Wing-Kin Ma, 'DOA Estimation of Quasi-Stationary Signals With Less Sensors Than Sources and Unkown Spatial Noise Covariance: A Khatri-Rao Subspace Approach', IEEE Trans.Signal Process., Vol.58, no.4 , pp.2168-2180, April (2010) SAR method (ISAR), Yoshida, 'Revised radar technology', IEICE, pp.280-283 (1996) SAR method (range compression), Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press, pp.131-149 (2003) SAR method (Az compression), Ouchi, 'Basics of Synthetic Aperture Radar for Remote Sensing', Tokyo Denki University Press, pp.171-178 (2003) CFAR processing, Yoshida, 'Revised radar technology', IEICE, pp.87-89 (1996) FMCW system (up-chirp and down-chirp), Yoshida, "Revised radar technology", IEICE, pp.274-275 (1996) FMICW, FRED E. Nathanson, 'RADAR DESIGN PRINCIPLES second edition', Scitech, pp452-454 (1999)

  As described above, in the conventional radar apparatus, in order to improve the range resolution, pulse compression or the like with a wide transmission frequency band is required. On the other hand, in order to improve the Doppler resolution, it is necessary to lengthen the observation time (increase the number of hits), and there is a problem that the search frame time decreases. For the above countermeasure, the extended array processing is applied. However, since there is a correlation between reflection points in the case of a radar target, a false target may be generated by the extended array processing.

  The present embodiment has been made in view of the above problems, and can provide a radar apparatus capable of increasing the resolution of at least one of range resolution and Doppler resolution even when the frequency band is relatively narrow or the observation time is relatively short. And a radar signal processing method thereof.

  In order to solve the above-described problem, the radar apparatus according to the present embodiment generates a range-Doppler image from a radar reception signal, extracts a reflection point Nall from the range-Doppler image using an amplitude threshold, and extracts the extracted reflection. The point Nall is separated into N (N ≦ Nall) groups of neighboring points and arranged on the range-Doppler axis (fast-slow-time axis) for each group, and the range axis (Nr point) and Doppler axis (Nd The extended array process is applied to at least one of the range axis and the Doppler axis obtained by inverse Fourier transform at each point) to obtain 2Nr-1 point or 2Nd-1 point, and the axis to which the extended array process is applied Is subjected to Fourier transform to form an image again, and the image result for the N points is subjected to amplitude superposition to output a high resolution image.

  That is, in each of different two-axis (A-axis and B-axis) signals, the target reflection point is separated by the range-Doppler axis and then subjected to an extended array process, so that even when there is a correlation like a radar target, Increase the resolution of the range-Doppler axis without generating false targets.

1 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to a first embodiment. The block diagram which shows the flow of the range-Doppler high resolution process at the time of applying an extended array process in the radar apparatus which concerns on 1st Embodiment. The conceptual diagram for demonstrating the ISAR process by the mounting radar of the radar apparatus which concerns on 1st Embodiment. The conceptual diagram which shows the flow of the process which acquires the high-resolution range-Doppler data from an ISAR image in the radar apparatus which concerns on 1st Embodiment. The block diagram which shows schematic structure of the transmission / reception system of the radar apparatus which concerns on 2nd Embodiment. The conceptual diagram which shows the flow of the process which acquires the high-resolution range-Doppler data from an ISAR image in the radar apparatus which concerns on 2nd Embodiment. The block diagram which shows schematic structure of the transmission / reception system of the radar apparatus which concerns on 3rd Embodiment. The conceptual diagram which shows the flow of the process which acquires the high-resolution range-Doppler data from an ISAR image in the radar apparatus which concerns on 3rd Embodiment. The block diagram which shows schematic structure of the transmission / reception system | strain of the radar apparatus which concerns on 4th Embodiment. The block diagram which shows schematic structure of the transmission / reception system | strain of the radar apparatus which concerns on 5th Embodiment. The wave form diagram which shows the signal waveform of the continuous wave sweep produced | generated as a transmission signal in the radar apparatus which concerns on 5th Embodiment. The conceptual diagram which shows the flow of the process which acquires the high-resolution range-Doppler data from an ISAR image in the radar apparatus which concerns on 5th Embodiment. The block diagram which shows schematic structure of the transmission / reception system | strain of the radar apparatus which concerns on 6th Embodiment. The wave form diagram which compares and compares the case of pulse transmission / reception and the case of continuous wave transmission / reception in the radar apparatus which concerns on 6th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First Embodiment) Expanded Array Processing After RD Axis Separation A radar apparatus according to the first embodiment will be described with reference to FIGS. Here, description will be made assuming a radar device for mounting a flying object (hereinafter referred to as an onboard radar).

  FIG. 1 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the present embodiment, FIG. 2 is a block diagram showing a specific processing flow for increasing the range-Doppler resolution, and FIG. 3 is an ISAR process by an on-board radar. FIG. 4 is a conceptual diagram showing a flow of processing for obtaining high-resolution range-Doppler data from an ISAR image.

This radar apparatus directs the beam so that the actual aperture beam is always irradiated to the target, and for each pulse transmitted at the PRI (Pulse Repetition Interval) interval within the synthetic aperture time (1 cycle), the range cell unit in the PRI Get data with. Using this acquired data, an ISAR (Inverse Synthetic Aperture Radar) process (see Non-Patent Document 2) is performed to obtain an ISAR image.

  In FIG. 1, a transmission signal generator 11 generates a pulse-modulated transmission signal. This transmission signal is distributed to N systems by a transmission distributor 12 and then directed to a transmission beam by a beam controller 13. Are phase-shifted by transmission phase shifters 141 to 14N in which the phase shift amounts corresponding to are set, are amplified by transmission amplifiers 151 to 15N, and are transmitted from antenna elements 171 to 17N via circulators 161 to 16N. .

  The reflected signal from the target is captured by the antenna elements 171 to 17N, amplified by the reception amplifiers 181 to 18N via the circulators 161 to 16N, and then subjected to low noise amplification, and then the phase shift amount corresponding to the reception beam by the beam controller 13 Are set by the reception phase shifters 191 to 19N and are combined by the reception synthesizer 20. The combined received signal is frequency-converted and AD-converted by the receiver 21 and output as a digital received signal. The range compressor 22 performs range compression by pulse compression, and the cross-range compressor 23 performs a slow-time axis ( Cross range compression is performed by FFT processing between PRIs), and reflection point extraction is performed by the reflection point extractor 24 using CFAR (see Non-Patent Document 5) or the like.

  The extracted reflection points are arranged on the range-Doppler axis (fast-slow-time axis) for each N (N ≦ Nall) group of neighboring points, and the IFFT processor 25 uses the range axis (Na point) and the Doppler axis. Each of (Nb points) is subjected to inverse FFT processing. Thereby, a signal corresponding to the phase gradient of the target signal is obtained on the range axis and the Doppler axis. This signal becomes the input vectors Xa (range axis) and Xb (Doppler axis) of the extended array processor 26.

  The extended array processor 26 (26a and 26b in FIG. 3) performs KR product array processing on the input vectors Xa (range axis) and Xb (Doppler axis) and outputs the processing result (Xkra, Xkrb) to a new extended array signal ( Xa, Xb). The signal subjected to the extended array processing is subjected to FFT processing on the range axis and the Doppler axis by an FFT processor 27 (27a and 27b in FIG. 3), thereby obtaining high-resolution range-Doppler data. The above is the process for one extracted point, and this is repeated N times corresponding to all the extracted points to obtain N range-Doppler data. This is added by the amplitude superimposing unit 28 (28a and 28b in FIG. 3) to obtain range-Doppler high resolution data.

  In the above configuration, the processing flow will be specifically described below.

First, range compression will be described (see Non-Patent Document 3). Range compression is a correlation process between an input signal and a range compression signal. The case of performing this in the frequency domain is formulated as follows.

The reference signal sref (linear chirp signal) can be expressed by the following equation.

The sample length of this reference signal sref (t) is replaced with a zero-padded signal in accordance with the input signal.

In order to replace it on the time axis, this s may be subjected to inverse Fourier transform. However, in order to perform the subsequent cross-range compression (23) (Az compression, see Non-Patent Document 4), ) Keep the axis. Next, cross range compression is performed, and the reference signal can be expressed by the following equation with reference to FIG.

The signal cs is obtained by multiplying the equations (3) and (6).

Using this, a signal fcs (ω, ku) is obtained by performing FFT processing on the u-axis.

The FFT image output can be calculated by inverse FFT with respect to the ω-axis of fcs.

Next, with reflection point extraction (24) by CFAR (see Non-Patent Document 5) or the like, the amplitude is predetermined in the XY axis (corresponding to the range-Doppler axis) image using the Σ system image output. Cells (Nall cells) exceeding the threshold are extracted.

This extracted signal is arranged on the range-Doppler axis (fast-slow-time axis) for each N (N ≦ Nall) group of neighboring points. Next, inverse FFT processing (25) is performed on the arranged extraction points on each of the range axis (Na point) and the Doppler axis (Nb point). Thereby, a signal corresponding to the phase gradient of the target signal can be obtained on the range axis and the Doppler axis. These signals become the input vectors Xa (range axis) and Xb (Doppler axis) for the extended array processing (26 (26a and 26b in FIG. 3)).

Next, KR product array processing (see Non-Patent Document 1) is performed as extended array processing using the signals (Xa, Xb) of the input vectors. First, the correlation matrix can be expressed by the following equation.

When the left and upper end elements are vectorized, the following equation is obtained.

  If Xkra and Xkrb are used as the new extended array signals (Xa and Xb) and FFT processing (27 (27a and 27b in FIG. 3)) is performed on the range axis and the Doppler axis, high-resolution range-Doppler data is obtained. be able to.

  The above is the processing for one extracted point, and N range-Doppler data are obtained by repeating this N times corresponding to all the extracted points, and this is subjected to amplitude superposition (28). An outline of the above processing is shown in FIG. 4A is an ISAR image on the range-Doppler plane, FIG. 4B is a separated image for each extraction point (A to E), and FIG. 4C is an extended array using range axis IFFT, extended array processing, and range axis FFT. As a result of processing + imaging processing, (d) shows an ISAR image in which images of respective extraction points are superimposed.

  As described above, according to the radar apparatus according to the present embodiment, after generating the range-Doppler image, the Nall points extracted by the amplitude threshold are separated into N (N ≦ Nall) groups of neighboring points, Each group is placed on the range-Doppler axis (fast-slow-time axis) and at least one of the range axis and the Doppler axis obtained by performing inverse FFT on each of the range axis (Nr point) and Doppler axis (Nd point) One extended array processing is applied to obtain 2Nr-1 (2Nd-1) points, and the expanded array processing axis is FFTed to form an image again. Get a good picture. That is, in each of different two-axis (A-axis and B-axis) signals, the target reflection point is separated by the range-Doppler axis and then subjected to an extended array process, so that even when there is a correlation like a radar target, High resolution of the range-Doppler axis can be achieved without generating a false target.

  Note that FIG. 3 is a diagram in the case of an on-board radar, but it is only necessary to obtain range-Doppler data (RD data), and an ISAR image is acquired when higher resolution is to be achieved. In addition, the radar apparatus may be a fixed radar (target is moving) as well as a case where the radar apparatus moves like an on-board radar. FIG. 4 shows the case where the extended array processing is applied to the range axis, but the same method can be applied to the Doppler axis. Further, in the present embodiment, the case has been described in which both the range axis and the Doppler axis are processed independently, but only one of the axes may be processed as necessary.

  In this embodiment, in order to improve the resolution of the RD data before the extended array processing, the contents of the ISAR (Inverse Synthetic Aperture Radar) processing are described. However, only normal range compression-cross range compression (FFT) is performed. It is also possible to generate RD data, extract points above a predetermined amplitude threshold, and perform processing of the expanded array.

(Second Embodiment) RD-axis Extended Array Processing, Parallel Processing A radar apparatus according to the second embodiment will be described with reference to FIGS.
In the first embodiment, the technique for increasing the resolution of either the range axis or the Doppler axis has been described. In this embodiment, an example in which high resolution is achieved for both axes will be described.

  FIG. 5 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the second embodiment. FIG. 6 is a process for obtaining high-resolution range-Doppler data from an ISAR image in the radar apparatus according to the second embodiment. It is a conceptual diagram which shows the flow of.

  In FIG. 5, after the generation of the range-Doppler image (˜23), Null point reflection point extraction (24) is performed, and the range axis KR processing (25R, 26R) is performed for each N (N ≦ Nall) group of neighboring points. , 29R, 27R) to obtain N pieces of RD data (1 to N). On the other hand, Doppler axis expansion array processing (25D, 26D, 29D, 27D) is performed for each N group. At this time, in order to match the resolution of the range axis and the Doppler axis, FFT processing (27R, 27D) is performed after zero padding (29R, 29D) of the range axis (Doppler axis). An image resulting from the KR processing of the range axis and the Doppler axis is superimposed (amplitude addition) (28) to obtain the entire high-resolution RD data (image). An overview of the above processing is shown in FIG.

  6, (a) is an ISAR image on the range-Doppler plane, (b) is a separated image for each extraction point (A to E), (c) is a range axis expansion array process, and (d) is a Doppler axis expansion array. Process (e) shows an ISAR image in which images of respective extraction points are superimposed.

  As described above, according to the radar apparatus according to the present embodiment, after generating the range-Doppler image, the Nall points extracted by the amplitude threshold are separated into N (N ≦ Nall) groups of neighboring points, After placing each group on the range-Doppler axis, IFFT processing for the range axis and Doppler axis, and applying the extended array processing, zero-filling is performed to match the resolution for the range axis and Doppler axis. The axis and the Doppler axis are subjected to FFT processing and imaged again, and the image result for N points is superimposed on the amplitude to obtain a high-resolution image. That is, by applying the extended array processing to both the range axis and the Doppler axis, it is possible to achieve high resolution at the same time for both axes.

(Third Embodiment) RD-axis Extended Array Processing, Cascade Processing A radar apparatus according to a third embodiment will be described with reference to FIGS.
In the second embodiment, a technique has been described in which both the range axis and the Doppler axis are increased in parallel and the resolution is increased by adding amplitude. In the present embodiment, an example will be described in which each axis is processed in order when increasing the resolution of both axes.

  FIG. 7 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the third embodiment. FIG. 8 is a process for obtaining high-resolution range-Doppler data from an ISAR image in the radar apparatus according to the third embodiment. It is a conceptual diagram which shows the flow of.

  In FIG. 7, the high resolution processing will be described in the order of the range axis and the Doppler axis, but the reverse case may be used. In FIG. 7, after the generation of the range-Doppler image (21 to 23), the reflection point extraction (241) of the Nall point is performed, and the range axis KR processing (25R, N) is performed for each N (N ≦ Nall) group of neighboring points. 26R, 27R) to obtain N pieces of RD data (1 to N). Next, N2all reflection points are extracted (242) for every N pieces of RD data. Although the number of reflection points may be different for each of the N sheets, for the sake of simplicity, for example, a number less than a predetermined number N2all is extracted. For each N2 (N2 ≦ N2all) group of neighboring points, the Doppler axis expansion array process is performed (25D, 26D, 27D). By the above processing, N × N 2 high-resolution RD data is obtained, and this is superimposed (amplitude addition) (28) to obtain the entire high-resolution RD data (image). An overview of the above processing is shown in FIG.

  8, (a) is an ISAR image on the range-Doppler plane, (b) is a separated image for each extraction point (A to E), (c) is range axis expansion array processing, and (d) is a Doppler axis expansion array. Process (e) shows an ISAR image in which images of respective extraction points are superimposed.

  As described above, according to the radar apparatus according to the present embodiment, after generating the range-Doppler image, the Nall points extracted by the amplitude threshold are separated into N (N ≦ Nall) groups of neighboring points, Each group is placed on the range-Doppler axis and the N2 points extracted by the amplitude threshold are separated from the result of applying the extended array processing to the range axis (Doppler axis), and the range-Doppler axis for each extracted point The Doppler axis (range axis) is subjected to extended array processing, the Doppler axis (range axis) is subjected to FFT processing and imaged again, and the image result for the N2 point is amplitude-superposed to produce a high-resolution image. obtain. That is, by applying the extended array processing to both the range axis and the Doppler axis, it is possible to achieve high resolution at the same time for both axes.

(Fourth Embodiment) Multiple times KR product A radar apparatus according to a fourth embodiment will be described with reference to FIG.
In the extended array processing in the first to third embodiments, the case where the KR product processing is performed only once has been described. However, in the KR product array, as shown in the equations (12) and (13), one processing is performed. In this case, since the real number (amplitude) is obtained by multiplying the wave source signal Xin and Xin ^* , the wave source signal remains a real number even if it is repeated a plurality of times, and there is no influence other than SN (signal to noise power ratio). For this reason, if it is more than predetermined SN, if the KR product array process is repeated a plurality of times, it is possible to further increase the resolution of the angle axis.

FIG. 9 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the fourth embodiment. In this case, the configuration (26a) in which the extended array process is performed a plurality of times is characteristic. In other words, if the initial array length is M, the array length becomes 2M-1 by one extended array process. For example, if it is repeated three times, the signal array length of the range axis (Doppler axis) is as follows: Become.

  This is equivalent to increasing the resolution of the range axis (Doppler axis) as the signal array length increases. The point that the KR product processing is performed a plurality of times (26a) is different from the first to third embodiments.

(Fifth Embodiment) Beat Frequency A radar apparatus according to a fifth embodiment will be described with reference to FIGS.
FIG. 10 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the fifth embodiment. FIG. 11 shows a signal waveform of a continuous wave sweep generated as a transmission signal in the radar apparatus according to the fifth embodiment. FIG. 12 is a conceptual diagram showing a flow of processing for obtaining high-resolution range-Doppler data from an ISAR image in the radar apparatus according to the fifth embodiment.

  In the extended array processing using a plurality of reflection points, it is important to reduce the correlation between the plurality of reflection points as much as possible. As a technique for this purpose, there is a technique for improving the range resolution by transmitting and receiving a broadband signal. However, in order to cope with a wideband signal, it is necessary to increase the range sampling speed, which increases the processing scale. For this measure, either a continuous wave sweep signal (see Non-Patent Document 6) or a pulse-modulated step frequency (see Non-Patent Document 7) is transmitted, and reception is performed by sweeping a local signal for observation by a beat frequency. There is a technique. In the radar apparatus shown in FIG. 10, the transmission signal generator 11a generates the sweep signal shown in FIG. 11, and the FFT processors 30, 31 receive Fast-time FFT (30), Slow-time as reception output on the reception side. Perform FFT (31) processing.

That is, the beat frequency fb is given by the following equation.

The beat frequency fb is determined from a target distance component and a target speed component. By sweeping the reception local signal, the frequency of the reception signal becomes a difference, and if the target distance or target speed is equal to or less than a predetermined value, the beat frequency is smaller than the sweep frequency band, so the receiver 21 is small. become.

  In the case of observation by beat frequency, as shown in FIG. 11, when the sweep time axis is fast-time and the axis between sweeps is slow-time, Fast-time FFT processing (30) is performed, and further, Slow-time FFT processing is performed. By performing (31), N reflection points can be extracted (24) on the range (Fast-time) axis-Doppler (Slow-time) axis. For each of the extracted reflection points, FIG. 12 (a) is an ISAR image on the range-Doppler plane, (b) is a separated image for each extraction point (AE), (c) is a range axis IFFT, and an extended array As shown in (D) shows an ISAR image in which the images of the respective extraction points are superimposed.) Similarly, if IFFT processing (25) is performed on the range axis (Doppler axis), an array signal fp (slow, fast) signal corresponding to the phase gradient can be obtained. If this is replaced with fp (t, ku) in the expression (10) of the first embodiment, the extended array signal is converted by the procedure of the expressions (11) to (14) in the same manner as in the first embodiment. The range axis Xkra and the Doppler axis Xkrb can be obtained. Further, if the FFT processing (27) is performed on the range axis and the Doppler axis to perform superposition (28), high-resolution range-Doppler data (fast time-slow time data) can be obtained.

  As described above, according to the radar apparatus of the fifth embodiment, the beat frequency is observed by transmitting and receiving a continuous sweep signal or a pulse frequency-modulated step frequency signal. That is, even when using a wideband signal to improve the range resolution by observing the beat frequency using a continuous sweep signal, the beat frequency is low, so the expanded array processing is used without increasing the hardware scale. The resolution of the range-Doppler axis can be increased.

(Sixth Embodiment) Long Distance Beat Frequency A radar apparatus according to a sixth embodiment will be described with reference to FIGS.
FIG. 13 is a block diagram showing a schematic configuration of a transmission / reception system of a radar apparatus according to the sixth embodiment, and FIG. 14 compares a case of pulse transmission / reception and a case of continuous wave transmission / reception in the radar apparatus according to the sixth embodiment. FIG.

  In the fifth embodiment, the observation method using the beat frequency has been described. In this case, due to the delay time due to the target distance, the beat frequency becomes high in the long distance, and the effect of reducing the reception frequency band by using the continuous wave becomes small. As a countermeasure, in this embodiment, as shown in FIG. 13, the receiver 32 shifts the start time of the local frequency in the time direction. As the shift time Td, a target observation distance range may be determined so that the beat frequency width becomes a predetermined value or less. The received signal is corrected by the range corrector 33 for the beat frequency of the target signal for each local signal shifted by the time Td. The subsequent processing is the same as in the fifth embodiment.

  If the target observation distance range is wide, divide the target observation distance range so that the observation beat frequency width is less than the predetermined value, prepare the receiving system for the number of divisions, and set the time delay of the local frequency do it. For the overlapping period of the divided local signals, the target distance may be calculated for the largest amplitude among the target reception amplitudes processed by each of the overlapping local signals. When the target distance can be limited to only a long distance, the time Td may be adjusted to set the local signal only in the observation time range.

  As described above, according to the radar apparatus of the sixth embodiment, the short-distance target received for each sweep is separated from the long-distance target received for each sweep after the time delay (Td) during beat frequency observation. For the long-distance target, the beat frequency including the beat frequency shift corresponding to Td is calculated, and the long-distance target is observed even with a narrow band receiver. That is, in the case of a long-distance target, it is received in a sweep after a time delay with respect to the distance, but it is separated from the short-distance target received for each sweep, and the long-distance is corrected by correcting the beat frequency by the time delay. Since the target beat frequency can be calculated correctly, the beat frequency is lowered, and the resolution of the range-Doppler axis can be increased by the extended array processing without increasing the hardware scale even with a narrowband receiver.

  As described above, the radar apparatus of each embodiment applies the extended array processing to the range-Doppler axis so that the range resolution or the Doppler resolution can be obtained even when the frequency band is relatively narrow or the observation time is relatively short. It is possible to increase the resolution of at least one of the above.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 11, 11a ... Transmission signal generator, 12 ... Transmission distributor, 13 ... Beam controller, 141-14N ... Transmission phase shifter, 151-15N ... Transmission amplifier, 161-16N ... Circulator, 171-17N ... Antenna Elements, 181 to 18N: receiving amplifier, 191 to 19N, receiving phase shifter, 20 ... receiving synthesizer, 21 ... receiver, 22 ... range compressor, 23 ... cross range compressor, 24, 241, 242 ... reflection point Extractor, 25, 25R, 25D ... IFFT processor, 26, 26a, 26b, 26R, 26D ... Extended array processor, 27, 27a, 27b, 27R, 27D ... FFT processor, 28, 28a, 28b ... Amplitude superposition 29R, 29D ... Zero padding processor, 30 ... Fast-time FFT processor, 31 ... Slow-time FFT processor, 32 ... Receiver, 33 ... Range corrector.

Claims (7)

Image generating means for generating a range-Doppler image from the radar received signal;
Extraction means for extracting a reflection point Nall from the range-Doppler image by an amplitude threshold;
The extracted reflection point Nall is separated into N (N ≦ Nall) groups of neighboring points and arranged on a range-Doppler axis (fast-slow-time axis) for each group, and the range axis (Nr point) And an extended array process that applies 2Nr-1 points or 2Nd-1 points by applying an extended array process to at least one of the range axis and the Doppler axis obtained by inverse Fourier transform at each of the Doppler axes (Nd points) Means,
Re-imaging means for re-imaging by Fourier transform for the axis to which the extended array processing is applied;
A radar apparatus comprising: a superimposing unit that superimposes an amplitude of the image result for the N points and outputs a high resolution image.   The extended array processing means performs zero padding for matching the resolution on the range axis and the Doppler axis based on the result of applying the extended array process after performing inverse Fourier transform on the range axis and the Doppler axis. Radar device. The extended array processing means separates the N2 points extracted by the amplitude threshold from the result of applying the extended array processing for the range axis or Doppler axis, and arranges each extracted point on the range-Doppler axis. Perform extended array processing for Doppler axis or range axis,
The superimposing means is a radar device that outputs an image with a high resolution by superimposing amplitude on the image result for the N2 point.   The radar apparatus according to any one of claims 1 to 3, wherein the extended array processing means performs the extended array processing Nkr times including amplitude normalization as necessary.   The radar apparatus according to claim 1, wherein the image generation unit generates a range-Doppler image by transmitting and receiving a continuous sweep signal or a pulse frequency modulated step frequency signal and observing a beat frequency.   The image generation means separates a short-distance target received for each sweep and a long-distance target received for each sweep after time delay (Td) at the time of beat frequency observation. 6. The radar apparatus according to claim 5, wherein a beat frequency is calculated including a corresponding beat frequency shift to observe a long distance target.   A range-Doppler image is generated from the received radar signal, a reflection point Nall is extracted from the range-Doppler image by an amplitude threshold, and the extracted reflection point Nall is separated into N (N ≦ Nall) groups of neighboring points. The range axis and the Doppler axis obtained by performing inverse Fourier transform on each of the range axis (Nr point) and the Doppler axis (Nd point) are arranged on the range-Doppler axis (fast-slow-time axis) for each group. Apply the extended array process to at least one of the points to obtain 2Nr-1 points or 2Nd-1 points, re-image the axis to which the extended array process has been applied by Fourier transform, and obtain the image results for the N points. A radar signal processing method of a radar apparatus that outputs a high-resolution image with amplitude superposition.

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