JP2019152500A - Radar system and radar signal processing method therefor - Google Patents

Abstract

To increase the resolution of a range or Doppler even when a frequency band is narrow or an observation time is short.SOLUTION: A radar system of an embodiment generates a range-Doppler (RD) image from a received radar signal and extracts a reflection point N, selects data of a prescribed range cell width by which a bank is selected for the range axis case and data of a prescribed bank width by which a range is selected for the Doppler axis case; separates the selected data of reflection points for each group of neighborhood points and arranges them on the range and the Doppler axes; forms the partial correlation matrix of range and Doppler axes using the range and Doppler axis data obtained by performing an FFT of the range axis and an IFFT of the Doppler axis; performs the extended array processing of the range and Doppler axes using a correlation matrix based on the average value of the partial correction matrix and performs an IFFT for the range axis and an FFT for the Doppler axis and visualizes again with regard to axes for which the extended array processing is performed, and amplitude superimposes the image results for N points and outputs a high-resolution image.SELECTED DRAWING: Figure 2

Description

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

  Conventional radar systems 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.

  Conventionally, an extended array process using a KR (Khatri-Rao) product array (see Non-Patent Document 1) or the like is applied for the above countermeasure. 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.

JP 2006-121935 A

KR product array, Wing-Kin Ma, 'DOA Estimation of Quasi-Stationary Signals With Less Sensors Than Sources and Unknown 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) Spatial averaging method, Kikuma, 'Adaptive signal processing with array antenna', Science and Technology Publishing, pp.163-170, 336-337 (1999) MUSIC, ESPRIT, Kikuma, 'Adaptive Antenna Technology', Ohm, pp.137-164 (2003)

  As described above, in the conventional radar system, in order to improve the range resolution, pulse compression or the like with a wide transmission frequency band is required, and thus a wide band is necessary. 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 a radar system capable of increasing the resolution of at least one of range resolution or 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 system 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 by an amplitude threshold, In the case of the range axis, the data of the predetermined range cell width with the bank selected is selected. In the case of the Doppler axis, the data of the predetermined bank width with the selected range is selected, and the selected data of the extracted reflection point Nall is in the vicinity. Are separated into N (N ≦ Nall) groups of points, and the selected data for each reflection point is arranged on the range axis and the Doppler axis for each group, and the Nr point on the range axis and the Nd point on the Doppler axis In the case of the range axis, the Fourier transform is performed, and in the case of the Doppler axis, the inverse Fourier transform is performed. Using the data of at least one of the range axis and the Doppler axis, a partial correlation matrix is formed by the Nrp point of the range axis or the Ndp point of the Doppler axis, and the correlation matrix by the average value of the partial correlation matrix is used. An extended array vector is extracted by performing an extended array process of 2Nrp-1 points of the range axis or 2Ndp-1 points of the Doppler axis. For the axis subjected to the extended array process, the range axis is inverse Fourier transform, Doppler The axis is subjected to Fourier transform and imaged again, and the image result for the N points is amplitude superimposed.

  That is, after separating the target reflection point on the range-Doppler axis, the array is further expanded using the averaged correlation matrix, so that even if there is a correlation like a radar target, a false target is not generated. Increase the resolution of the range-Doppler axis.

1 is a block diagram showing a schematic configuration of a transmission system of a radar system according to a first embodiment. 1 is a block diagram showing a schematic configuration of a receiving system of a radar system 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 system which concerns on 1st Embodiment. The conceptual diagram for demonstrating the ISAR process by the mounted radar to which the radar system which concerns on 1st Embodiment was applied. The figure which shows the range axis arithmetic processing of the radar system which concerns on 1st Embodiment. The figure which shows the Doppler axis calculation process of the radar system 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 system which concerns on 1st Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system 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 system which concerns on 2nd Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system 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 system which concerns on 3rd Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system which concerns on 4th Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system which concerns on 5th Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system which concerns on 6th Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system which concerns on 7th Embodiment. The block diagram which shows schematic structure of the receiving system of the radar system which concerns on 8th 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) Extended Array Processing After RD Axis Separation A radar system according to the first embodiment will be described with reference to FIGS. Here, a description will be given assuming a radar system mounted on a flying object (hereinafter referred to as an on-board radar).

  1 is a block diagram illustrating a schematic configuration of a transmission system of a radar system according to the present embodiment, FIG. 2 is a block diagram illustrating a schematic configuration of a reception system of the radar system according to the present embodiment, and FIG. 3 is a range-Doppler high resolution. FIG. 4 is a conceptual diagram for explaining ISAR processing by an on-board radar to which the present embodiment is applied, FIG. 5 is a diagram showing range axis calculation processing, and FIG. FIG. 7 is a conceptual diagram showing a flow of processing for obtaining high-resolution range-Doppler data from an ISAR image.

  First, in the transmission system shown in FIG. 1, a reference signal for transmission generated by a transmission signal generator 11 is modulated by a chirp signal by a modulator 12, converted to a radio frequency (RF) signal by a frequency converter 13, and a pulse The signal is modulated by the modulator 14 and transmitted from the transmission antenna 15.

  Next, in the reception system shown in FIG. 2, the reflected signal from the target is captured by the reception antenna 21, frequency-converted to baseband by the receiver 22, and then converted to a digital signal. Thereafter, the range compressor 23 performs range compression by pulse compression, and the cross range compressor 24 performs FFT (Fast Fourier Transform) at a PRI (Pulse Repetition Interval) interval on the slow-time axis. Perform cross-range compression.

  Next, the reflection point extractor 25 extracts reflection points by CFAR (Constant False Alarm: Constant False Alarm Probability) (see Non-Patent Document 5) or the like, and uses the range-Doppler data to obtain the XY axis (range- (Corresponding to the Doppler axis) In the image, the cells (Nall) of the reflection points whose amplitude exceeds the predetermined threshold are extracted, and the reflection point selector 26 is used for each N (N ≦ Nall) group of nearby points. It is arranged on the range-Doppler axis (fast-slow-time axis) shown in FIG.

  Next, in a range axis FFT / Doppler axis IFFT (Inverse Fast Fourier Transform) 27, at least an FFT process of the range axis (Na point) and an IFFT process of the Doppler axis (Nb point) are performed on the extracted cell. Do either one. Here, in order to suppress the correlation between the reflection points, as shown in FIG. 3, the partial correlation matrix averaging processor 28 separates the correlation matrix of the range axis and the Doppler axis into partial matrices and averages them (non-null). (See Patent Document 6). The FFT output of the range axis becomes the input vector Xa of the extension processor 29, and the IFFT output of the Doppler axis becomes the input vector Xb of the extension processor 29.

  Next, using the input vector signals (Xa, Xb), the extended processor 29 performs KR product array processing (see Non-Patent Document 1). After the extended array processing, the range axis IFFT / Doppler axis FFT2A performs IFFT processing on the extended array output Xa in the case of the range axis (Na point), and FFT processing on the extended array output Xb in the case of the Doppler axis (Nb point). Thus, high-resolution range-Doppler data is obtained. The processing for one point extracted in this way is repeated N times corresponding to all the extracted points, and is superposed by the superimposer 2B to obtain range-Doppler data.

  In the radar system configured as described above, specific processing contents of the present embodiment will be described with reference to FIGS. 4 to 7.

  In the case of an aircraft-mounted radar, the radar system according to the present embodiment directs the beam so that the actual aperture beam is always irradiated to the target on the flight path as shown in FIG. Then, as shown in FIGS. 5A to 5D, for each pulse transmitted at PRI (Pulse Repetition Interval) (corresponding to transmission / reception data interval) within the synthetic aperture time (1 cycle), Data is acquired in units of range cells, and ISAR (Inverse Synthetic Aperture Radar) processing (see Non-Patent Document 2) is performed using the acquired data.

  FIG. 4 is a diagram in the case of an on-board radar. In this embodiment, it is sufficient that range-Doppler data (RD data) is obtained, and an ISAR image is obtained when higher resolution is to be achieved. Further, the radar system may be not only moved as in the case of the on-board radar but also fixed (the target is moving).

  First, range compression (23) will be described (see Non-Patent Document 3). The range compression is a correlation process between an input signal and a range compression signal. When this is performed in the frequency domain, it is expressed by the following equation.

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

  This reference signal sref (t) is replaced with a signal in which the sample length is zero-padded according to the input signal.

  The signal s may be IFFT-processed on the time axis. However, in order to perform cross-range compression (24) (Az compression, see Non-Patent Document 4) thereafter, the signal s is converted to (ω, u). Keep the axis. Next, cross range compression is performed, and the reference signal can be expressed by the following equation.

  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 (range-Doppler data) can be calculated by IFFT processing related to the ω axis of fcs.

  The above processing is processing for performing range compression and cross-range compression, but in order to make the explanation easy to understand, in FIG. 5, cross range compression is shown in FIG. 5 (a), and FIG. 5 (b) is shown as range compression. Describe. Needless to say, the cross range compression is performed after the range compression.

  Next, as shown in FIG. 5C, the reflection point extraction (25) by CFAR (see Non-Patent Document 5) or the like is used to use the range-Doppler data to correspond to the XY axis (corresponding to the range-Doppler axis). ) Select cells (Nall cells) whose amplitude exceeds a predetermined threshold in the image. For each extracted point, after selecting a bank in descending order of amplitude, data of a predetermined range cell width is extracted. This extracted signal is arranged on the range-Doppler axis (fast-slow-time axis) for each N (N ≦ Nall) group of neighboring points by reflection point selection (26).

  Next, the selected cell is subjected to FFT processing for the range axis (Na point) or Doppler axis (Nb point), IFFT processing for the range axis, and IFFT processing for the Doppler axis (27). A signal corresponding to the phase gradient of the signal can be obtained. These signals become the input vectors Xa (range axis) and Xb (Doppler axis) for the extended array processing (29).

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

  Next, in order to suppress the correlation between the reflection points, as shown in FIG. 5D, a method (28) of dividing the correlation matrix into sub-matrices and averaging is applied (see Non-Patent Document 6). . First, for the range axis Rxxa, the following equation is obtained. Since a plurality of target signals transmitted and received by the radar system are correlated with each other, in order to suppress the correlation component of the correlation matrix Rxxa of Xa, Nap cells are extracted in order from the signal length of Xa. Perform the calculation.

  For the time average of CPI units, for example, Rxxap is calculated by an average process using a forgetting factor.

On the other hand, as shown in FIGS. 6A to 6C, the Doppler axis Rxxbb is obtained by the following equation similarly to the range axis. That is, FIG. 6A shows a process in which range axis compression and cross range compression are performed, and FIG. 6B shows a state in which a cell whose amplitude exceeds a predetermined threshold is selected by extraction of a reflection point by CFAR or the like. Show. For each extracted reflection point, after selecting a range in descending order of amplitude, data of a predetermined bank width is extracted. In order to suppress the correlation component of the Xb correlation matrix Rxxb using this data, as shown in FIG. 6C, Nbp cells are extracted in order from the Xb signal length, and Rxxb is calculated each time. Do.

For the time average in CPI units, for example, Rxxbp is calculated by an average process using a forgetting factor.

  Using Rxxap and Rxxbp, which are the average values of the partial correlation matrix, vectorizing the left and upper end elements by the extended array process (29) yields the following equation.

  If this Xkra, Xkrb is used as a new extended array signal (Xa, Xb) and FFT / IFFT (2A) is performed on the range axis or Doppler axis, high-resolution range-Doppler data can be obtained.

  The above is the process for one extracted point. This is repeated N times corresponding to all the extracted points, and N range-Doppler data are obtained, and this is subjected to amplitude superposition (2B).

  The above outline is shown in FIG. First, the ISAR image shown in FIG. 7A is created from the range-Doppler data, and points A to E that are features of the image are extracted. Next, as shown in FIG. 7B, the extracted points A to E are separated and subjected to FFT processing on the range axis, averaging of the partial correlation matrix, extended array processing, and then IFFT processing. As shown in FIG. 7 (c), N expansion array processing results are superimposed, and an ISAR image is added as shown in FIG. 7 (d), thereby obtaining high-resolution range-Doppler data.

  Although FIG. 7 shows the case where the extended array processing is applied to the range axis, 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.

  Further, in this embodiment, in order to improve the resolution of the RD data before the extended array processing, it has been described in the contents of the ISAR processing. However, only the normal range compression-cross range compression (FFT) is used to convert the RD data. The expanded array may be processed by extracting and extracting points that are above a predetermined amplitude threshold.

  As described above, in the radar system according to the first 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, and the group At least one of the range axis and the Doppler axis obtained by IFFT processing on each of the range axis (Nr point) and the Doppler axis (Nd point), arranged on the range-Doppler axis (fast-slow-time axis) A partial correlation matrix by Nrp (Ndp) points is formed using the data of one axis, and an extended array vector of 2Nrp-1 (2Ndp-1) points is extracted using the correlation matrix by the average value. The array-processed axis is subjected to FFT processing to form an image again, and the image result for N points is superimposed on the amplitude to obtain a high-resolution image.

  That is, in this embodiment, after the target reflection point is separated by the range-Doppler axis, the array is further expanded using the averaged correlation matrix, so that even if there is a correlation such as a radar target, a false target is detected. It is possible to increase the resolution of the range-Doppler shaft without generating it.

Second Embodiment (RD axis extended array processing, parallel processing)
In the first embodiment, the method of increasing the resolution of at least one of the range axis and the Doppler axis after separating the reflection points on the range-Doppler axis has been described. In the second embodiment, a case will be described in which high resolution is achieved for both axes.

  FIG. 8 is a block diagram showing a schematic configuration of a receiving system of the radar system according to the second embodiment. Since the transmission system is the same as that of the first embodiment, description thereof is omitted here.

  In the receiving system of the radar system shown in FIG. 8, after the generation of the range-Doppler image, the reflection point extraction unit 25 extracts the reflection point of the Nall point, and the reflection point of the range axis is sent to the reflection point selection unit 26R. The reflection points are distributed to 26D. In the range axis, the selected reflection point is FFT processed (27R), the partial correlation matrix is averaged (28R), and the extended array (KR) processing of the range axis is performed for each N (N ≦ Nall) group of neighboring points. (29R) to obtain N pieces of RD data (1 to N). On the other hand, in the Doppler axis, the selected reflection point is subjected to IFFT processing (27D), the partial correlation matrix is averaged (28D), and the expanded array (KR) processing of the Doppler axis is performed for each N group (29D). At this time, in order to match the resolution of the range axis and the Doppler axis, zero filling is performed on each of the range axis and the Doppler axis (2CR, 2CD), IFFT processing is performed on the range axis (2AR), and FFT processing is performed on the Doppler axis (2AD). ). An image resulting from the KR processing of the range axis and the Doppler axis is superimposed (amplitude addition) (2B) to obtain the entire high-resolution RD data (image).

  An outline of the above processing is shown in FIG. First, the ISAR image shown in FIG. 9A is created from the range-Doppler data, the points A to E that are characteristic of the image are extracted, and the points A to E extracted as shown in FIG. 9B. Separate every time. Subsequently, the FFT processing is performed on the range axis, the partial correlation matrix is averaged, the extended array processing is performed, and then the IFFT processing is performed. The IFFT processing is performed on the Doppler axis, the partial correlation matrix is averaged, and the extended array processing is performed. After that, by performing FFT processing, superimposing N expansion array processing results on each of the range axis and the Doppler axis as shown in FIG. 9C, and adding an ISAR image as shown in FIG. 9D, High resolution range-Doppler data can be obtained.

  As described above, in the radar system according to the second 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 arranged on a range-Doppler axis, and after IFFT processing is performed on the range axis and the Doppler axis, a partial correlation matrix is formed by Nrp (Ndp) points, and 2Nrp-1 (2Ndp -1) Extracting the extended array vector of points and zero-filling the range axis and Doppler axis to match the resolution, then performing FFT processing on the range axis and Doppler axis, re-imaging, and image for N points The result is amplitude superimposed to obtain a high resolution image.

  That is, in this embodiment, by performing an extended array process using an averaged correlation matrix for both the range axis and the Doppler axis, even if there is a correlation like a radar target, a false target is not generated. The resolution of the range-Doppler axis can be increased.

(Third embodiment) (RD axis extended array processing, cascade processing)
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 third embodiment, an example will be described in which each axis is processed in order when increasing the resolution of both axes.

  FIG. 10 is a block diagram showing a schematic configuration of a receiving system of a radar system according to the third embodiment. Since the transmission system is the same as that of the first embodiment, description thereof is omitted here.

  In FIG. 10, the case where the Doppler axis processing is performed after the range axis processing is described as the order of resolution enhancement, but the reverse case may be used. In the radar system shown in FIG. 10, after the range-Doppler image is generated by the receiving antenna 21, the receiver 22, the range compressor 23, and the cross range compressor 24, the reflection point extraction unit 25 extracts the reflection point of the N1all point, The reflection point selection unit 26R selects the reflection point of the range axis. Next, the selected reflection point of the range axis is subjected to FFT processing (27R), the partial correlation matrix is averaged (28R), and the extended array of range axis (KR) for each N1 (N1 ≦ Nall) group of neighboring points Processing is performed (29R), N1 RD data (1 to N1) are obtained, range axis zero padding processing is performed (2CR), and range axis IFFT processing is performed (2AR). Subsequently, for each of the N pieces of RD data, the reflection point extraction unit 25a extracts the reflection points of the N2all point of the Doppler axis. 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 reflection point selection unit 26D selects a reflection point on the Doppler axis, performs IFFT processing on the selected reflection point (27D), and averages the partial correlation matrix ( 28D), Doppler axis expansion array (KR) processing is performed for each N2 group (29D). Next, zero padding processing of the Doppler axis is performed (2CD), and FFT processing is performed (2AD). The image resulting from the KR processing of the range axis and the Doppler axis is superimposed (amplitude addition) (2B) to obtain the entire high-resolution RD data (image).

  With the above processing, N1 × N2 high-resolution RD data is obtained, and is superposed (amplitude addition) to obtain the entire high-resolution RD data (image). An outline of the above processing is shown in FIG. First, the ISAR image shown in FIG. 11A is created from the range-Doppler data, the points A to E that are characteristic of the image are extracted, and the points A to E extracted as shown in FIG. 11B. Separate every time. Subsequently, the FFT processing is performed on the range axis, the partial correlation matrix is averaged, the extended array processing is performed, and then the IFFT processing is performed. As shown in FIG. 11C, N1 extended array processing is performed on the range axis. Next, IFFT processing is performed on the Doppler axis, the partial correlation matrix is averaged, extended array processing is performed, and then FFT processing is performed. As shown in FIG. 11D, N2 extended array processing is performed on the Doppler axis. Finally, the extended array processing results are superimposed, and an ISAR image is added as shown in FIG. 11E to obtain high-resolution range-Doppler data.

  As described above, the radar system according to the third embodiment, after generating the range-Doppler image, separates the N1all points extracted by the amplitude threshold into N1 (N1 ≦ N1all) groups of neighboring points, For each group, it is arranged on the range-Doppler axis, and for the range axis (or Doppler axis), a partial correlation matrix by Nrp (or Ndp) points is formed, and a correlation matrix by its average value is used to calculate 2Nrp-1 (or 2Ndp-1) Extracts the extended array vector of points, separates the N2all points extracted by the amplitude threshold, separates each N2 (N2≤N2all) group of extracted points, and sets the range-Doppler axis for each group , Doppler axis (or range axis) FFT processing (or IFFT processing) to image again, image results for N2 points are superimposed on amplitude, and high resolution Obtain an image. That is, after performing an extended array process using a correlation matrix averaged on the range axis (or Doppler axis), an extended array process is performed using the correlation matrix averaged on the Doppler axis (or range axis), thereby providing radar. Even when there is a correlation like a target, the resolution of the range-Doppler axis can be increased without generating a false target.

  In the present embodiment, since the resolution of the Doppler axis (or range axis) is increased after the resolution of the range axis (or Doppler axis) is increased, the processing scale increases compared to the second embodiment, but the range-Doppler A higher resolution can be achieved with the shaft.

(Fourth Embodiment) Range Axis Extended Array Processing In the first to third embodiments, the case of high resolution using the data of the 2-axis range-Doppler axis has been described. In the fourth embodiment, a case of increasing the resolution of one axis of the range axis will be described.

  FIG. 12 is a block diagram showing a schematic configuration of a receiving system of a radar system according to the fourth embodiment. Since the transmission system is the same as that of the first embodiment, description thereof is omitted here.

  In the radar system shown in FIG. 12, after the range image is generated by the receiving antenna 21, the receiver 22, and the range compressor 23, the reflection point extraction unit 25 extracts the reflection point of the Nall point, and the reflection point selection unit 26R extracts the range axis. Select the reflection point. Next, the selected reflection point of the range axis is subjected to FFT processing (27R), the partial correlation matrix is averaged (28R), and the extended array of range axis (KR) for every N (N ≦ Nall) groups of neighboring points. Perform processing (29R) to obtain N range data (1 to N), execute the range axis IFFT processing (2AR), superimpose the results for N points (2B), and overall Obtain high-resolution range axis data.

  That is, in the first embodiment, the reflection point is separated by the range-Doppler axis before the extended array processing, but the present embodiment is different in that the reflection point is separated only by the range axis. After separating the reflection points, extended array processing is performed using an averaged correlation matrix based on a partial correlation matrix, and FFT processing is performed to output high-resolution data on the range axis.

  As described above, the radar system according to the fourth embodiment, after generating the range compressed data, separates the Nall points extracted by the amplitude threshold into N (N ≦ Nall) groups of neighboring points, Each is arranged on the range axis (fast-time axis), and by using the range axis data obtained by FFT processing on each of the range axes (Nr points), a partial correlation matrix by Nrp (Ndp) points is formed, Using the correlation matrix based on the average value, an extended array vector of 2Nrp-1 (2Ndp-1) points is extracted, the axis subjected to the extended array processing is subjected to IFFT processing and compressed again, and the result for N points is obtained. High-resolution output is obtained on the range axis by superimposing the amplitude. That is, in the present embodiment, by performing an extended array process using an averaged correlation matrix on the range axis, even if there is a correlation such as a radar target, a false target is not generated and the range axis height is increased. Resolution can be improved.

(Fifth Embodiment) (Expansion array processing of Doppler shaft)
In the first to third embodiments, the case of increasing the resolution using the data of the two-axis range-Doppler axis is described, and in the fourth embodiment, the case of increasing the resolution of one axis of the range axis has been described. In the fifth embodiment, an increase in resolution in the case of one Doppler axis will be described.

  FIG. 13 is a block diagram showing a schematic configuration of a receiving system of a radar system according to the fifth embodiment. Since the transmission system is the same as that of the first embodiment, description thereof is omitted here.

  In the radar system shown in FIG. 13, after the Doppler image is generated by the FFT 23a instead of the reception antenna 21, the receiver 22, and the range compressor, the reflection point extraction unit 25 extracts the reflection point of the Nall point, and the reflection point selection unit 26D Select the Doppler axis reflection point. Next, IFFT processing is performed on the reflection points on the selected Doppler axis (27D), the partial correlation matrix is averaged (28D), and an expanded array of Doppler axes (KR) for each N (N ≦ Nall) group of neighboring points. Perform processing (29D), obtain N range data (1 to N), execute FFT processing of Doppler axis (2AD), superimpose the result for N point (2B), Doppler axis To obtain high resolution output.

  That is, in the first embodiment, the reflection points are separated by the range-Doppler axis before the extended array processing, but the present embodiment is different in that the reflection points are separated only by the Doppler axis. After separating the reflection points, extended array processing is performed using an averaged correlation matrix based on a partial correlation matrix, and FFT processing is performed to output high-resolution data of the Doppler axis.

  As described above, the radar system according to the fifth embodiment, after generating Doppler axis data, separates the Nall points extracted by the amplitude threshold into N (N ≦ Nall) groups of neighboring points, Each is arranged on the Doppler axis (slow-time axis), and the Doppler axis data obtained by IFFT processing on each of the Doppler axes (Nd points) is used to form a partial correlation matrix by Nrp (Ndp) points, Using the correlation matrix based on the average value, an extended array vector of 2Nrp-1 (2Ndp-1) points is extracted, the axis subjected to the extended array processing is subjected to FFT processing, and the result of N points is superimposed on the amplitude. Get high resolution output with Doppler axis. That is, by performing extended array processing using an averaged correlation matrix on the Doppler axis, even if there is a correlation like a radar target, it is possible to increase the resolution of the Doppler axis without generating a false target. it can.

(Sixth embodiment) (multiple KR products)
In the first to fifth embodiments, the extended array processing is performed by one KR product array. In the KR product array, since the real number (amplitude) is obtained by multiplying the wave source signal Xin and Xin * by one processing as shown in the equation (12)), the wave source signal remains a real number even if it is repeated a plurality of times. Yes, there is no effect other than SN (signal to noise power ratio). For this reason, if it is more than predetermined SN, if the KR product array processing is repeated a plurality of times, it is possible to further increase the resolution of the angle axis.

  FIG. 14 is a block diagram showing a schematic configuration of a receiving system of a radar system according to the sixth embodiment. Since the transmission system is the same as that of the first embodiment, the description thereof is omitted here. Further, in FIG. 14, the difference from the first embodiment is that a plurality of KR product processes (29a) are performed, and other configurations are the same as those of the first embodiment. Is omitted.

  That is, if the initial array length is M, the array length becomes 2M-1 by one extended array process. Therefore, for example, when the number of repetitions is repeated three times, the signal array length of the range axis (Doppler axis) is as follows: become.

  Increasing the signal array length is equivalent to increasing the resolution of the range axis (or Doppler axis).

  As described above, the radar system according to the sixth embodiment performs the extended array process Nkr times including the amplitude normalization as necessary to increase the resolution of the range axis or the Doppler axis. In other words, by repeating the extended array processing multiple times using the averaged correlation matrix, even if there is a correlation like a radar target, the resolution of the range or Doppler axis can be further improved without generating a false target. Can do.

(Seventh embodiment) (MUSIC, ESPRIT)
In the first to sixth embodiments, the method for forming the extended array to improve the resolution has been described. In the seventh embodiment, a method of applying an eigenvalue analysis method (MUSIC, ESPRIT, etc., see Non-Patent Document 7) using an extended array will be described. At this time, since the averaging of the partial correlation matrix is used before the extended array is formed and the reflection points are uncorrelated, no further submatrix averaging method is required.

  FIG. 15 is a block diagram showing a schematic configuration of the receiving system of the radar system according to the seventh embodiment in the case of two axes of a range axis and a cross range axis. In FIG. 15, the process up to the expansion array process (29) is the same as that of the first embodiment. The eigenvalue analysis process (2D) is executed. The MUSIC process is formulated below (see Non-Patent Document 7).

  MUSIC processing is performed using this Rxx, and a MUSIC spectrum is calculated by the following equation (see Non-Patent Document 5).

  In the case of one axis, one of the PRI axis and the range frequency axis may be deleted. In the case of ESPRIT, since it is described in Non-Patent Document 7, it is omitted.

  In the case of two axes, there is processing of a range axis and a Doppler axis. A specific example is shown in FIG. In this case, as shown in FIG. 16, each of the range axis and the Doppler axis is processed as in the second embodiment, and the eigenvalue analysis results (2DR, 2DD) of the range axis and the Doppler axis are superimposed (2B). )do it.

  As described above, the radar system according to the seventh embodiment applies the eigenvalue analysis method (MUSIC, ESPRIT, etc.) to the output subjected to the extended array processing, thereby achieving high resolution of the range axis or Doppler axis. . In this way, by applying the eigenvalue analysis method to the output of the extended array processing, it is possible to further increase the resolution of the range-Doppler axis.

  In the above-described embodiment, after the reflection points are separated into either the range axis or the Doppler axis for the range axis and the Doppler axis, a plurality of values are obtained by using the averaging method of the partial correlation matrix of the signal sequence. A method for improving the resolution of the range axis or Doppler axis by forming an extended array by the KR product array after suppressing the correlation of the reflection points has been described. Needless to say, this method can be applied to increase the resolution of the angle axis by applying a spatial averaging method (see Non-Patent Document 6), which is an averaging method of the correlation matrix in the angle axis. In this case, a partial correlation matrix is formed based on the signal vector of the antenna array element, and after performing spatial averaging, the extended array may be extracted.

  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 ... Transmission signal generator, 12 ... Modulator, 13 ... Frequency converter, 14 ... Pulse modulator, 15 ... Transmission antenna,
21 ... Receiving antenna, 22 ... Receiver, 23 ... Range compressor, 24 ... Cross range compressor, 25 ... Reflection point extractor, 26, 26R, 26D ... Reflection point selector, 27 ... Range axis FFT / Doppler axis IFFT 27R ... Range axis FFT, 27D ... Doppler axis IFFT, 28, 28R, 28D ... Partial correlation matrix averaging processor, 29, 29R, 29D ... Expanded array processor, 29a ... Multiple expanded array processor, 2A ... Range Axis IFFT / Doppler Axis FFT, 2AR ... Range Axis IFFT, 2AD ... Doppler Axis FFT, 2B Point Superimposer, 2CR, 2CD ... Zero Filler, 2DR, 2DD ... Eigenvalue Analyzer.

Claims (8)

Generate a range-Doppler image from the radar received signal,
A reflection point Nall is extracted from the range-Doppler image by an amplitude threshold;
For each reflection point, in the case of the range axis, select the data of the predetermined range cell width that selected the bank, in the case of the Doppler axis, select the data of the predetermined bank width that selected the range,
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the selected data for each reflection point for each group on the range axis and Doppler axis,
At least one of the Nr point of the range axis and the Nd point of the Doppler axis, Fourier transform is performed for the range axis, and inverse Fourier transform is performed for the Doppler axis.
Using the data of at least one of the range axis and the Doppler axis obtained by the Fourier transform and the inverse Fourier transform, a partial correlation matrix by the Nrp point of the range axis or the Ndp point of the Doppler axis is formed.
An extended array vector is extracted by performing an extended array process of 2Nrp-1 points on the range axis or 2Ndp-1 points on the Doppler axis using a correlation matrix obtained by averaging the partial correlation matrices,
For the axis subjected to the extended array processing, the range axis is inverse Fourier transformed, the Doppler axis is Fourier transformed and imaged again,
A radar system that superimposes the image results for the N points with amplitude. Generate a range-Doppler image from the radar received signal,
A reflection point Nall is extracted from the range-Doppler image by an amplitude threshold, and for each reflection point, data of a predetermined range cell width in which a bank is selected in the case of a range axis, and a predetermined bank in which a range is selected in the case of a Doppler axis. Select width data,
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the data set for the reflection point for each group on the range axis and the Doppler axis,
The range axis performs Fourier transform, the Doppler axis performs inverse Fourier transform,
Using the range axis and Doppler axis data obtained by the inverse Fourier transform, a partial correlation matrix is formed by the Nrp point of the range axis and the Ndp point of the Doppler axis,
An extended array vector is extracted by performing an extended array process of 2Nrp-1 points on the range axis and 2Ndp-1 points on the Doppler axis using a correlation matrix obtained by averaging the partial correlation matrices,
For the range axis and Doppler axis, perform zero padding to match the resolution,
The range axis is inverse Fourier transformed, the Doppler axis is Fourier transformed and imaged again,
A radar system that superimposes the amplitude of the image result for the N points imaged again. Generate a range-Doppler image from the radar received signal,
The reflection point Nall is extracted from the range-Doppler image by the amplitude threshold, and in the case of the range axis, data of a predetermined range cell width in which the bank is selected is selected, and in the case of the Doppler axis, data of a predetermined bank width in which the range is selected is selected. And
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the selected data of the reflection point for each group on the range axis,
Perform Fourier transform of the range axis,
Using the data of the range axis obtained by the Fourier transform, a partial correlation matrix by Nrp points of the range axis is formed,
An extended array vector is extracted by performing an extended array process of 2Nrp-1 points on the range axis using a correlation matrix based on an average value of the partial correlation matrix,
Perform zero padding to match the resolution with the Doppler axis for the range axis,
Perform an inverse Fourier transform on the range axis and re-image,
Place the selected data of the reflection point for each group on the Doppler axis,
Performing an inverse Fourier transform of the Doppler axis,
Using the Doppler axis data obtained by the inverse Fourier transform, a partial correlation matrix by Ndp points of the Doppler axis is formed.
An extended array vector is extracted by performing an extended array process of 2Ndp-1 points on the Doppler axis using a correlation matrix based on an average value of the partial correlation matrix,
Perform zero padding to match the resolution with the range axis for the Doppler axis,
Perform Fourier transform on the Doppler axis and re-image,
A radar system that superimposes the image results of the N points on the range axis and the N points on the Doppler axis that have been imaged again. Generate range image from radar received signal,
The reflection point Nall is extracted from the range image by the amplitude threshold,
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the selected data of the reflection point for each group on the range axis,
Perform Fourier transform of the range axis,
Using the data of the range axis obtained by the Fourier transform, a partial correlation matrix by Nrp points of the range axis is formed,
An extended array vector is extracted by performing an extended array process of 2Nrp-1 points on the range axis using a correlation matrix based on an average value of the partial correlation matrix,
Perform inverse Fourier transform on the range axis and re-compress and image,
A radar system that superimposes the imaged N-point image result of the range axis. Generate Doppler image from radar received signal,
A reflection point Nall is extracted from the Doppler image by an amplitude threshold,
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the selected data of the reflection point for each group on the Doppler axis,
Performing an inverse Fourier transform of the Doppler axis,
Using the Doppler axis data obtained by the inverse Fourier transform, a partial correlation matrix by Nrp points of the Doppler axis is formed.
An extended array vector is extracted by performing an extended array process of 2Ndp-1 points on the Doppler axis using a correlation matrix based on an average value of the partial correlation matrix,
Perform Fourier transform on the Doppler axis and recompress and image,
A radar system that superimposes the imaged image results of N points of the Doppler axis in amplitude.   The radar system according to claim 1, wherein the extended array process is performed a plurality of times including amplitude normalization.   The radar system according to claim 1, wherein an eigenvalue analysis technique is applied to the output subjected to the extended array processing. Generate a range-Doppler image from the radar received signal,
The reflection point Nall is extracted from the range-Doppler image by the amplitude threshold, and in the case of the range axis, data of a predetermined range cell width in which the bank is selected is selected, and in the case of the Doppler axis, data of a predetermined bank width in which the range is selected is selected. And
Separating the selected data of the extracted reflection points Nall into N (N ≦ Nall) groups of neighboring points;
Place the selected data of the reflection point for each group on the range axis and the Doppler axis,
At least one of the Nr point of the range axis and the Nd point of the Doppler axis, Fourier transform is performed for the range axis, and inverse Fourier transform is performed for the Doppler axis.
Using the data of at least one of the range axis and the Doppler axis obtained by the Fourier transform and the inverse Fourier transform, a partial correlation matrix by the Nrp point of the range axis or the Ndp point of the Doppler axis is formed.
An extended array vector is extracted by performing an extended array process of 2Nrp-1 points on the range axis or 2Ndp-1 points on the Doppler axis using a correlation matrix obtained by averaging the partial correlation matrices,
For the axis subjected to the extended array processing, the range axis is inverse Fourier transformed, the Doppler axis is Fourier transformed and imaged again,
A radar signal processing method of a radar system for superimposing an amplitude of an image result for the N points.

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