JP6367134B2 - Radar apparatus and radar signal processing method - Google Patents

Description

  The present embodiment relates to a radar apparatus and a radar signal processing method.

  In a radar apparatus, as a method for identifying a target by an image, the center of gravity of the target is tracked by both the range and Doppler axes, the center of the image is acquired, and the range compression and the AZ compression are performed. An ISAR (Inverse Synthetic Aperture Radar) process for imaging a target is known (see Non-Patent Document 1). In the conventional ISAR processing, when calculating the center of gravity, the resolution and accuracy of the range-Doppler frequency axis are low, so that the error is large, the SN (signal power / noise power) is low, and the image is deteriorated. there were.

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) SAR processing method (Polar format conversion reconstruction process), MEHRDAD SOUMEKH, “Synthetic Aperture Radar Signal Processing”, JOHN WILEY & SONS, INC., Pp.319-325 (1999) Phase monopulse (phase comparison monopulse) method, IEICE, revised radar technology, pp.262-264 (1996) Amplitude monopulse (amplitude comparison monopulse) system, IEICE, revised radar technology, pp.260-262 (1996) MUSIC, ESPRIT, Kikuma, Adaptive Antenna Technology, Ohmsha, pp.137-164 (2003) Spatial averaging method, Kikuma, adaptive signal processing with array antenna, Science and Technology Publishing, pp.163-170, pp.336-337 (1999)

JP 2010-271115 A

  As described above, in the ISAR processing applied to the conventional radar apparatus, when calculating the center of gravity, the resolution and accuracy of the range-Doppler frequency axis are low, so the error is large and SN (signal power / noise power). ) Becomes low, and there is a problem that the image deteriorates.

  The present embodiment has been made in view of the above-described problem, and it is possible to observe a representative point such as a target center of gravity with high accuracy or high resolution, thereby reducing an ISAR image with good SN and little deterioration. An object of the present invention is to provide a radar apparatus and a radar signal processing method thereof.

  In order to solve the above-described problem, the present embodiment tracks a target acquired from a received signal of a real aperture antenna on both the range and Doppler frequency axes, obtains the image center of the target, and performs range compression and AZ compression. In this way, in the ISAR (Inverse Synthetic Aperture Radar) type radar apparatus that images the target on the range-Doppler frequency axis, the N means for the synthetic aperture length is obtained from the received signal of the real aperture antenna by the dividing means. (N is a natural number of 1 or more) Hit pulses are divided into M (N is a natural number of 2 or more) for every N2 hits including overlapping, and each of the divided received signals is divided by the range-Doppler monopulse calculation means. Performs Doppler processing and pulse compression processing, and detects and detects range cells with multiple extreme values by CFAR (Constant False Alarm Rate) processing For a cell, the Doppler frequency is calculated by monopulse processing using the Σ signal and Δ signal on the Doppler axis, the range is calculated by monopulse processing using the Σ signal and Δ signal on the range axis, and M ranges by Doppler An approximate curve of phase change is calculated, a reference signal calculation means calculates a reference signal for cross-range compression of ISAR processing based on the approximate curve, and an imaging means calculates the reception signal based on the reference signal Signal range compression and AZ compression are performed to generate a target ISAR image.

1 is a block diagram showing a configuration of a radar apparatus according to a first embodiment. The block diagram which shows the structure of a monopulse process part in the radar apparatus shown in FIG. The conceptual diagram for demonstrating the outline | summary of the ISAR process in a synthetic aperture in the radar apparatus shown in FIG. The figure which shows a mode that the data sequence for every PRI is extracted from the acquisition data by a synthetic aperture in the radar apparatus shown in FIG. The figure which shows the approximated curve produced | generated as a reference signal in the radar apparatus shown in FIG. The figure which shows the relationship between an error voltage and a range in the radar apparatus shown in FIG. The figure which shows the relationship between an error voltage and a Doppler frequency in the radar apparatus shown in FIG. The figure which shows the mode of the image conversion by the coordinate conversion based on a range and a measured angle value in the radar apparatus shown in FIG. The figure which shows the procedure which acquires the SAR image in the radar apparatus shown in FIG. The figure which shows a mode that the data of a lattice point are produced | generated by polar format conversion in the radar apparatus shown in FIG. The block diagram which shows the structure of the radar apparatus which concerns on 2nd Embodiment. FIG. 12 is a block diagram showing a configuration of a high resolution processing unit in the radar apparatus shown in FIG. 11. The figure for demonstrating the calculation method of a MUSIC spectrum in the radar apparatus shown in FIG. The figure for demonstrating the averaging process between several target signals in the radar apparatus shown in FIG.

  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)
The radar apparatus according to the first embodiment will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing the configuration of the radar apparatus according to the first embodiment. In the radar apparatus shown in FIG. 1, the antenna 1 is a phased array antenna formed by arranging a plurality of antenna elements to form a large aperture array. The antenna 1 is repeatedly supplied from the transmitting / receiving unit 21 of the transmitter / receiver 2 at a specific cycle. A transmission pulse signal having a frequency (hereinafter referred to as a PRF (Pulse Repetition Frequency) signal) is transmitted in a specified direction and the reflected wave is received. The transceiver 2 forms a received beam in an arbitrary direction by performing phase control on the signals received by the plurality of antenna elements of the antenna 1 in the transceiver unit 21 according to instructions from the beam controller 22 and combining them. To obtain a PRF received signal. Here, the beam control unit 22 performs phase control corresponding to each beam on the transmission / reception unit 21 so as to form a Σ beam, a ΔAZ beam, and a ΔEL beam based on the angle measurement value in the designated target direction. As a result, the transmitting / receiving unit 21 generates a Σ signal, a ΔAZ signal, and a ΔEL signal and outputs them to the narrowband processing unit A of the signal processor 3.

  The Σ signal, ΔAZ signal, and ΔEL signal input to the narrowband processing unit A are converted into digital signals for each system by AD (Analog-Digital) conversion units 311, 312, and 313. The digitized Σ signal, ΔAZ signal, and ΔEL signal are sent to the data extraction units 321, 322, and 323 in each system. The data extraction units 321, 322, and 323 pass the inputted Σ signal, ΔAZ signal, and ΔEL signal through a predetermined frequency filter in order to reduce the sampling rate and reduce the processing scale, and then PRI (Pulse Repetition Interval) The data in is acquired by the range cell unit. The range cell signals of Σ, ΔAZ, and ΔEL obtained by the data extraction units 321, 322, and 323 are converted into frequency domain signals of the PRI axis by PRI axis FFT (Fast Fourier Transformation) processing units 331, 332, and 333, respectively. Subsequently, the range (time) compression units 341, 342, and 343 perform pulse compression on the range axis to form a range compressed signal.

  Among these, the Σ-system range compressed signal is sent to a CFAR (Constant False Alarm Rate) processing unit 35, and a range cell having a plurality of extreme values is detected by the CFAR processing. For the range cell detected here, the threshold detector 36 detects a range cell having an extreme value equal to or greater than a threshold value and outputs the range compression signal. Further, the range compression signals of the ΔAZ system and the ΔEL system are sent to the cell detection units 371 and 372, respectively, and the signals of the range cells corresponding to the range cells detected by the threshold detection unit 36 of the Σ system are extracted, respectively. Together with the signal of the detection cell of the system, it is sent to the angle measuring unit 38, where angle calculation in the target direction is performed. The angle measurement value obtained by the angle measurement unit 38 is sent to the beam control unit 22 as a target direction.

  On the other hand, the Σ-system received signal digitized by the AD conversion unit 311 is sent to the data extraction unit 39 of the broadband processing unit B. The data extraction unit 39 observes the Doppler range of the representative point such as the target center of gravity, directs the beam in the target direction, and generates a reference signal for AZ compression based on the Doppler range information. Extract data for The extracted data is pulse-compressed on the range axis by the range compressor 3A. This pulse compression signal is sent to the AZ compression unit 3B, subjected to cross range compression (AZ compression) based on the reference signal generated by the range / Doppler monopulse calculation unit 3C and the reference signal generation unit 3D, and then converted to a polar format. Is sent to the imaging unit 3E. The imaging unit 3E converts the received signal subjected to the range / cross-range compression into a frequency domain signal by two-dimensional FFT processing, performs image processing by polar format conversion, and converts the received signal into the time domain by two-dimensional inverse FFT processing. Return to signal and image. The imaging unit 3E may be used to improve image quality and can be omitted.

  Here, the range / Doppler monopulse processing section 3C is specifically configured as shown in FIG. First, the output (N bank) of the Σ-system PRI axis FFT processing unit 331 is input to the bank selection unit 3C1 together with the detection result of the threshold detection unit 36. In the bank selection unit 3C1, a bank including the maximum value is selected based on the detection result of the threshold detection unit 36. The signals of the selected bank are converted into frequency domain signals on the range axis by the range axis FFT processing unit 3C2, and sent to the multiplication unit 3C3. On the other hand, the reference signal generation unit 3C4 generates a Σ series reference signal (for example, a linear chirp signal) used in the range axis phase monopulse. This reference signal is converted into a frequency domain signal by the reference signal FFT processing unit 3C5, then sent to the multiplication unit 3C3, and multiplied by the bank signal in the frequency domain.

  Next, the output of the multiplication unit 3C3 is sent to the Σ weight multiplication unit 3C6, and is multiplied by a Σ weight for generating a Σ signal with reduced side lobes. The Σ signal multiplied by the Σ weight is converted into a time domain signal by the Σ inverse FFT processing unit 3C7 and sent to the range axis monopulse processing unit 3C8. The output of the multiplication unit 3C3 is sent to the Δ weight multiplication unit 3C9, and is multiplied by the Δ weight for generating a Δ signal with reduced side lobes. The Δ signal multiplied by the Δ weight is converted into a time domain signal by the Δ inverse FFT processing unit 3C10 and sent to the range axis monopulse calculation unit 3C8. The range axis monopulse calculation unit 3C8 calculates an error signal due to the range axis phase monopulse from the Σ signal and the Δ signal on the time axis. This error signal is converted into a range axis by the range calculator 3C11 and output to the reference signal generator 3D.

  On the other hand, the output PRI (N hit) of the Σ-system data calculation unit 321 becomes a Δ signal in which the Δ weight is multiplied by the Δ weight multiplication unit 3C12 to reduce the side lobe, and the PRI axis FFT processing unit 3C13 outputs the PRI axis. The signal is converted into a frequency domain signal, and a Δ signal including the maximum value is selected based on the detection result of the threshold detection unit 36 in the bank selection unit 3C14. The selected Δ signal is pulse-compressed on the range axis by the range compressor 3C15. This pulse-compressed Δ signal is sent to the frequency axis monopulse unit 3C16 together with the Σ signal from the Σ inverse FFR processing unit 3C7. The frequency axis monopulse unit 3C16 calculates an error signal due to both frequency axis phase monopulses. This error signal is converted into a Doppler axis by the Doppler calculation unit 3C17 and output to the reference signal generation unit 3D.

  The contents of signal processing in the radar apparatus having the above configuration will be described below.

  In the first embodiment, as shown in FIG. 3, the actual aperture beam by the on-board radar is controlled so as to always irradiate the target, and as shown in FIG. 4, the PRI interval (PRI1 to PRIN) within the synthetic aperture time. ), Data is acquired in units of range cells in the PRI and repeatedly processed for each CPI (CPI1 to CPIM). Using this acquired data, ISAR processing is performed to obtain an ISAR image. Although FIG. 3 shows an example of the on-board radar, the radar may be fixed if an ISAR image can be obtained.

  In the radar apparatus shown in FIG. 1, the antenna 1 and the transmitter / receiver 2 direct the beam to a range to be imaged by beam control, and send the received signal to the signal processor 3. The signal processor 3 converts the received signal into a digital signal by AD conversion (311 to 313). The beam directing direction is a direction obtained by measuring the target direction by narrow-band processing with a small processing scale. The digital signal after AD conversion of Σ, ΔAZ, and ΔEL of the narrowband processing system of FIG. 1 is input, and after filtering at a predetermined frequency to satisfy the sampling frequency in order to lower the sampling rate than data extraction, Sampling is performed (321 to 323). This signal is converted into the frequency domain by PRI axis FFT processing (331 to 333), subjected to range compression (pulse compression) (341 to 343), Σ signal is subjected to CFAR processing (35), and threshold detection is performed (36). ). The ΔAZ and ΔEL cells corresponding to the detected cells are extracted (371, 372), and the angle is measured using the detected Σ signal and the extracted ΔAZ and ΔEL signals (38). The beam is directed and controlled in the direction of the angle measurement value.

Next, processing for observing a range-Doppler of a representative point such as a target center of gravity using a Σ-system PRI axis FFT output will be described. As shown in FIG. 3 and FIG. 4, N-hit PRI data including duplicates is extracted from the data Nall acquired for the synthetic aperture to PRI1 to PRIN, and CPI (m) (m = 1 to M ), The above processing is performed for each CPI. In the reference signal generation, an approximate curve of the reference signal Ref (reference signal for AZ compression) is calculated based on the range obtained for each CPI and the observed value of Doppler as shown in FIG. This is formulated as follows.

Here, as a method for improving the accuracy of the target signal range r and Doppler fd, which is the subject of the present embodiment, a method using monopulse processing on the range axis and the Doppler axis (see Patent Document 1) will be described.

  A method of using weights for the PRI data string to generate the Σ signal and the Δ signal will be described. With reference to FIG. 2, a series of processes will be described below.

First, of the Σ-system PRI axis FFT processing outputs (331 to 333), the bank including the maximum value is selected (3C1), and is subjected to FFT processing on the range axis (3C2).

Next, a reference signal of Σ used in the range axis phase monopulse described later (here, a linear chirp signal, but other modulation schemes such as a non-linear chirp signal and code modulation may be used) (3C4). This can be expressed as follows:

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

The reference signal is subjected to FFT processing (3C5), thereby obtaining a frequency axis signal of the reference signal.

When this is multiplied by the input signal in the frequency domain (3C3), the following equation is obtained.

Next, the side lobes are reduced, and weights for generating Σ and Δ signals are set by Σ weight multiplication and Δ weight multiplication (3C6, 3C9). As the weight, a Taylor weight (cited document 3) or the like may be selected according to the setting of the range side lobe.

These are subjected to Σ inverse FFT and Δ inverse FFT (3C7, 3C9) to obtain the following equation.

It should be noted that the term of the exponential function of SΔ has the same phase shift between Σ and Δ.

Further, the time axis t is converted to the range axis R by the relationship of the following equation.

From the result of Σ in equation (9), detection cells (time samples) m (m = 1 to M) whose amplitude exceeds a predetermined threshold are extracted, and range axis monopulse calculation (3C8) is performed for each detection cell. The following equation is used.

  For the error voltage and range, as shown in FIG. 6, the error voltage for the range is tabulated in advance and an error voltage table is created. Based on the observed value ε calculated by the equation (11), the range Rmono is calculated and output using a table. This method can be said to be a method in which the phase monopulse method (see Non-Patent Document 5) as an angle measurement method is replaced with a range axis (time axis).

  The method using the phase monopulse has been described above, but other methods such as an amplitude monopulse method (see Non-Patent Document 6) may be used.

  As another embodiment, there is a method for improving the Doppler frequency observation accuracy. For this purpose, monopulse processing is performed on the Doppler axis in the same manner as the range axis (see Patent Document 1).

First, in the Σ system in the system of FIG. 2, a bank having the maximum value of the PRI axis FFT output is selected using the detection result (3C1), and range compression (3C2 to 3C7) is performed to obtain Σ (f). . On the other hand, the Δ system receives a PRI signal, performs Δ weight multiplication (3C12), divides N hits into 1 to N / 2 and N / 2 + 1 to N, multiplies the weights, and performs PRI axis FFT processing. (3C13) to obtain a Doppler axis Δ signal. Among the Δ signals, the bank is selected by the detection signal (bank number) (3C14), the range is compressed (3C15), and the Δ (f) signal is obtained. Using the Σ (f) and Δ (f) signals, an error voltage for frequency axis monopulse processing (3C16) is obtained by the following equation.

  Next, in Doppler calculation (3C17), the error voltage reference value ε0 calculated using the frequency characteristics of Σ (f) and Δ (f) stored in advance as shown in FIG. 7 is tabulated (ε0 and frequency f), and using the reference table, the Doppler frequency fmono is calculated from the observed value ε and output.

  In addition, about weighting, in addition to -1 or 1, you may multiply weights, such as a Taylor way, in order to reduce a side lobe.

An image as shown in FIG. 8 can be obtained by the range Rmono and Doppler fmono calculated by the above monopulse method. From the plurality of reflection points, for example, the center of gravity calculation of the following equation is performed to extract a representative point of the target image.

  By substituting the range Rmono_t and Doppler fmono_t of representative points for each CPI (m = 1 to M) into (1) and (2), a highly accurate reference signal can be obtained.

  Next, a description will be given of the wideband processing of FIG. 1 in which imaging is performed using this reference signal. The monopulse output Σ of the antenna 1 is converted into a digital signal by AD conversion (311), sampled by data extraction (39), and subjected to correlation calculation with a reference signal for range compression corresponding to the waveform of the modulation signal (3A ) And AZ compression by correlation calculation using the reference signal generated by the equation (1) (3B). This is formulated as follows.

First, range compression will be described (see Non-Patent Document 2). Range compression is a correlation process between an input signal and a range compression signal. The case where this is performed in the frequency domain is formulated as follows.

In order to make it on the time axis, the signal s may be subjected to inverse Fourier transform. However, in order to perform AZ compression (see Non-Patent Document 3), the signal s is kept on the (ω, u) axis. Next, cross range compression is performed, and the reference signal uses the equation (1). In the equation (1), the same value is assumed for the ω axis.

The signal cs is obtained by multiplying the equations (17) and (18).

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

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

Next, as a more accurate image generation method, SAR image processing (3E) by polar format conversion will be described with reference to FIGS. 9 and 10 (see Non-Patent Document 4). Data acquisition (t, u) (step S1), FFTx (ω, u) (step S2), range compression and reference signal multiplication (ω, u) (step S3), the output s of equation (17) for pulse compression The processes up to are the same as described above. Therefore, first, Fourier transform is performed with respect to the u axis using this s (step S4).

Next, a reference signal for AZ compression is generated.

Further, kx and ky can be obtained by the following equations.

For the image center, for example, the range of CPIm (m = 1 to M) and the AZ angle and EL angle of the angle measurement (38) used when generating the reference signal in the reference signal generation (3D) of FIG. Or an approximate curve for each m of the range, AZ angle, and EL angle is calculated, and the approximate curve is used as the position calculated by the following equation.

Using this AZ compression reference signal, fsm is calculated by the following equation (step S5).

Polar format conversion shown in FIGS. 9 and 10 is performed using fsm, and grid point data F (kx, ky) is generated on the kx and ky axes (step S6). Polar format conversion is a method of calculating the data of grid points on the (kx, ky) axis using the acquired data using an interpolation method or the like, and details are as described in Non-Patent Document 4. I will omit it. Using this fsm, an image using polar format conversion is output by two-dimensional inverse FFT (step S7).

  Image processing by this polar format conversion is not always necessary, and may be used to improve image quality.

  As described above, in the ISAR, the radar apparatus according to the first embodiment divides N hit pulses for the synthetic aperture length into M ways of N2 hits including overlap, and performs Doppler processing and pulses for each division. After compression processing and detection by CFAR, the Doppler axis for the detected cell is calculated by monopulse processing by Σd and Δd, the range is calculated by monopulse processing by Σr and Δr for the range axis, and M types An approximate curve of phase change due to range-Doppler is calculated, and a reference signal for cross-range compression of ISAR processing is calculated based on the curve to obtain an ISAR image. In this way, since the representative point such as the target center of gravity is observed with high accuracy or high resolution, the SN is improved, thereby reducing image degradation.

(Second Embodiment)
The method of the first embodiment is effective when the number of target reflection points is small. However, when the number of reflection points increases, there are cases where the representative points cannot be separated due to a mixture of reflection points. The radar apparatus according to the second embodiment includes a countermeasure technique.

  FIG. 11 is a block diagram illustrating a configuration of a radar apparatus according to the second embodiment. However, in FIG. 11, the same reference numerals as those in FIG.

  In FIG. 11, the difference from the first embodiment is that a range-Doppler mono-pulse calculation unit 3C is used instead of the range-Doppler monopulse calculation unit 3C. That is, the transmission / reception signals directed in the target direction by the beam directing control of the beam control unit 22 are converted into digital signals by the AD conversion units 311 to 313 for each of Σ, ΔAZ, and ΔEL in the signal processor 3. In the Σ, ΔAZ, and ΔEL signals converted into digital signals, necessary data is extracted by the data extraction units 321 to 323 in order to reduce the sampling rate. The extracted data is converted into a frequency domain signal of the PRI axis by the PRI axis FFT processing units 331 to 333 and then sent to the range compression units 341 to 343. Among these, the Σ-system PRI axis FFT output is input to the range-Doppler high resolution processing unit 3F, which is a feature of the present embodiment. Details of the system of the range-Doppler high resolution processing unit 3F are shown in FIG. 12, and will be described below with reference to equations and FIG.

First, the input signal Sin (Doppler bank signal) of the range-Doppler high resolution processing unit 3F is a result of the PRI axis FFT of the Σ series extraction data (FIG. 13A).

In the range-Doppler high resolution processing unit 3F, the input signal (Doppler bank signal) Sig is converted into a frequency domain signal of the range axis by the range axis (time axis) FFT processing unit 3F1 (FIG. 13B).

On the other hand, the reference signal generation unit 3F3 generates a Σ-series reference signal (for example, a linear chirp signal). The case of a linear chirp signal is expressed as follows.

As this reference signal, other modulation methods such as a non-linear chirp signal and code modulation may be used.

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

The time axis reference signal generated in this manner is converted into a frequency axis signal by the reference signal FFT processing unit 3F4.

The frequency domain reference signal is sent to the multiplier 3F2 and is multiplied by the frequency domain range axis Doppler bank signal. Thereby, the bank signal after multiplication of the reference signal is expressed by the following equation.

Next, a weight multiplier 3F5 calculates and multiplies a weight for reducing the range side lobe after pulse compression. As the weight, a uniform weight, a tailor weight, or the like may be selected according to the setting of the range side lobe.

Next, the bank signal after the weight multiplication is converted into a time domain signal of the range axis by the inverse FFT process of the range axis IFFT processing unit 3F6, and converted to a Doppler range by the Doppler range output unit 3F7 (FIG. 13 (FIG. 13). c)).

The relationship between the time axis t and the range axis R is as follows. Hereinafter, when ranges and times are notated together, they are converted according to the relationship of the following equation.

The CFAR detection unit 3F8 performs CFAR detection on the signal S (n, t) (expressed in time) on the time (range) axis, and the time tsel (p) and Doppler frequency fsel (p) ( (N, M) cells centered on p is the target number) are extracted.

Next, the Doppler inverse FFT / range FFT processing unit 3F10 performs inverse FFT on the extracted cell Doppler axis to convert it to the PRI axis (FIG. 13 (d)), and FFT the range axis to convert it to the range frequency axis. These signals are rearranged one-dimensionally as Sw (pri, ω) (FIG. 13E). Based on the rearranged signal X, a covariance matrix Rxx is calculated. Formulated below.

Next, the correlation matrix is averaged by the average correlation matrix calculation unit 3F11, the MUSIC processing unit 3F12 is used for MUSIC processing using the calculation result Rxx, and the MUSIC spectrum is calculated by the following equation (FIG. 13 (f)) (See Patent Document 5).

In the MUSIC spectrum Smusic, the maximum value Ω (ft, ωt) of the signal exceeding the threshold is extracted by, for example, CFAR processing (3F13). From the Doppler frequency ft and the range frequency ωt, the Doppler range output unit 3F14 calculates the target Doppler frequency ft and range Rt by conversion of the following equation.

The above describes the case where the correlation between the target signals is small. Since the plurality of target signals transmitted and received by the radar have a correlation with each other, an averaging process is performed to suppress the correlation component of Rxx in equation (37). For this purpose, as shown in FIG. 14, the partial matrix Swm is extracted from the matrix data of the PRI-range frequency axis (FIG. 14 (a)), and Rxxm is sequentially calculated for the extracted partial matrix (FIG. 14). (B)) Let Rxx be a matrix of average values for each element.

Using this average Rxx, the target Doppler (velocity) and range are calculated by the equations (38) to (40).

  11 and 12, the range compression is performed inside the range-Doppler high resolution processing unit 3F. However, by using the output of the Σ system range compression unit 341 in FIG. It may be reduced.

  The main point of the present embodiment is to obtain an average value of a correlation matrix based on a two-dimensional signal and perform MUSIC processing. The averaging method is an average value of each correlation matrix or a forward-backward spatial average. Other methods such as a law (see Non-Patent Document 8) may be used.

  The MUSIC processing has been described above, but other high resolution processing such as ESPRIT (see Non-Patent Document 7) may be used.

If the high resolution processing result of the Doppler range axis is as shown in FIG. 8 as in the first embodiment, the representative point is extracted from the plurality of reflection points in FIG.

  By substituting the representative point range Rhreso_t and Doppler fhreso_t into the equations (1) and (2), a highly accurate reference signal can be obtained, and a highly accurate ISAR image is obtained using this reference signal. be able to.

  In the above embodiment, the method of generating the reference signal for AZ compression with high accuracy using the monopulse processing or high resolution processing of the range-Doppler axis has been described, but without using the monopulse processing or high resolution processing. Also, a method of obtaining a reference signal by substituting into the equations (1) and (2) using the range and Doppler observed from the data of CPI1 to CPIM in FIG.

  In addition, the present embodiment 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 1 ... Antenna, 11 ... Transmitting antenna element, 2 ... Transmitter / receiver, 21 ... Transmitter / receiver, 22 ... Beam controller, 3 ... Signal processor, 311, 312, 313 ... AD converter, A ... Narrowband processor, 321 323 ... Data extraction unit, 331 to 333 ... PRI axis FFT processing unit, 341 to 343 ... Range (time) compression unit, 35 ... CFAR processing unit, 36 ... Threshold detection unit, 371, 372 ... Cell detection unit, 38 ... Angle measuring unit, B ... wideband processing unit, 39 ... data extraction unit, 3A ... range compression unit, 3B ... range compression unit, 3C ... range-Doppler monopulse calculation unit, 3D ... reference signal generation unit, 3E ... by polar format conversion Imaging unit, 3F ... range-Doppler high resolution processing unit, 3F1 ... range axis FFT processing unit, 3F2 ... multiplication unit, 3F3 ... reference signal generation, 3F4 ... reference signal FF Processing unit, 3F5 ... weight multiplication unit, 3F6 ... range axis IFFT processing unit, 3F7 ... Doppler range output unit, 3F8 ... CFAR detection unit, 3F9 ... Doppler range cell extraction unit, 3F10 ... Doppler inverse FFT / range FFT processing unit, 3F11: average correlation matrix calculation unit, 3F12: MUSIC processing unit, 3F13: CFAR processing unit, 3F14: Doppler range output unit.

Claims (8)

The target acquired from the received signal of the real aperture antenna is tracked on both the range and Doppler frequency axes, and the target is imaged on the range-Doppler frequency axis by obtaining the target image center and performing range compression and AZ compression. In the ISAR (Inverse Synthetic Aperture Radar) type radar device,
A dividing unit that divides pulses of N (N is a natural number of 1 or more) hit with respect to a synthetic aperture length into M (M is a natural number of 2 or more) for each N2 hits including overlapping, from the received signal of the real aperture antenna;
Each of the divided received signals is subjected to Doppler processing and pulse compression processing, a range cell having a plurality of extreme values is detected by CFAR (Constant False Alarm Rate) processing, and a Σ signal on the Doppler axis is detected for the detected cell. Range-Doppler that calculates the Doppler frequency by monopulse processing using the Δ and Δ signals, calculates the range by monopulse processing using the Σ signal and Δ signal on the range axis, and calculates the approximate curve of the phase change by M range-Doppler Monopulse calculation means;
Reference signal calculation means for calculating a reference signal for cross-range compression of ISAR processing based on the approximate curve;
A radar apparatus comprising: imaging means for generating a target ISAR image by performing range compression and AZ compression of the received signal based on the reference signal.   The radar apparatus according to claim 1, wherein the imaging unit performs an imaging process by polar format conversion after the AZ compression. The target acquired from the received signal of the real aperture antenna is tracked on both the range and Doppler frequency axes, and the target is imaged on the range-Doppler frequency axis by obtaining the target image center and performing range compression and AZ compression. In the ISAR (Inverse Synthetic Aperture Radar) type radar device,
A dividing unit that divides pulses of N (N is a natural number of 1 or more) hit with respect to a synthetic aperture length into M (M is a natural number of 2 or more) for each N2 hits including overlapping, from the received signal of the real aperture antenna;
Applying Doppler processing and pulse compression processing to each of the divided received signals, detecting range cells having a plurality of extreme values by CFAR (Constant False Alarm Rate) processing, extracting predetermined cells around the detected cells, A range-Doppler monopulse calculating means for calculating a Doppler frequency by high-resolution processing for the Doppler axis, calculating a range by high-resolution processing for the range axis, and calculating an approximate curve of phase change by M ranges-Doppler ,
Reference signal calculation means for calculating a reference signal for cross-range compression of ISAR processing based on the approximate curve;
A radar apparatus comprising: imaging means for generating a target ISAR image by performing range compression and AZ compression of the received signal based on the reference signal.   The radar apparatus according to claim 3, wherein the imaging unit performs an imaging process by polar format conversion after the AZ compression. The target acquired from the received signal of the real aperture antenna is tracked on both the range and Doppler frequency axes, and the target is imaged on the range-Doppler frequency axis by obtaining the target image center and performing range compression and AZ compression. In the ISAR (Inverse Synthetic Aperture Radar) type radar signal processing method,
Dividing N (N is a natural number of 1 or more) hit pulses for the synthetic aperture length from the received signal of the real aperture antenna into M (M is a natural number of 2 or more) N2 hits each including N overlapping pulses,
Each of the divided received signals is subjected to Doppler processing and pulse compression processing, a range cell having a plurality of extreme values is detected by CFAR (Constant False Alarm Rate) processing, and a Σ signal on the Doppler axis is detected for the detected cell. The Doppler frequency is calculated by monopulse processing using the Δ and Δ signals, the range is calculated by monopulse processing using the Σ signal and Δ signal on the range axis, and the approximate curve of the phase change by M range-Doppler is calculated.
Calculate a reference signal for cross-range compression of ISAR processing based on the approximate curve,
A radar signal processing method for generating a target ISAR image by performing range compression and AZ compression of the received signal based on the reference signal.   6. The radar signal processing method according to claim 5, wherein the ISAR image is generated by performing an imaging process by polar format conversion after the AZ compression. The target acquired from the received signal of the real aperture antenna is tracked on both the range and Doppler frequency axes, and the target is imaged on the range-Doppler frequency axis by obtaining the target image center and performing range compression and AZ compression. In the ISAR (Inverse Synthetic Aperture Radar) type radar signal processing method,
Dividing N (N is a natural number of 1 or more) hit pulses for the synthetic aperture length from the received signal of the real aperture antenna into M (M is a natural number of 2 or more) N2 hits each including N overlapping pulses,
Applying Doppler processing and pulse compression processing to each of the divided received signals, detecting range cells having a plurality of extreme values by CFAR (Constant False Alarm Rate) processing, extracting predetermined cells around the detected cells, The Doppler axis is calculated by high resolution processing for the Doppler axis, the range is calculated by high resolution processing for the range axis, and an approximate curve of phase change by M range-Doppler is calculated.
Calculate a reference signal for cross-range compression of ISAR processing based on the approximate curve,
A radar signal processing method for generating a target ISAR image by performing range compression and AZ compression of the received signal based on the reference signal.   8. The radar signal processing method according to claim 7, wherein the ISAR image is generated by performing an imaging process by polar format conversion after the AZ compression.

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