JP6363524B2 - 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 process, when a rigid target is moving, the Doppler speed at each reflection point on the target varies depending on the rotational movement of the target. For this reason, the image generated by the ISAR process is usually different from the true target shape and is also different from the absolute value of the shape dimension.

  Therefore, in the method for identifying a target using an ISAR image, the shape and size of the generated image may be significantly different from the true target due to a change in Doppler speed due to the rotation or vibration of the target, and it may be difficult to identify the target. .

  In addition, when a specific point within a target having a size is detected and tracked based on an ISAR image, there is a problem that the error is large and tracking cannot be performed because the cross range is different from the absolute value.

  In addition, when measuring a target having a size in a Doppler radar or the like that does not generate an ISAR image, vector synthesis (complex synthesis) of a plurality of points in which the angle measurement points are widened, resulting in increased glint noise. There was a problem that the accuracy of angle measurement was also lowered.

  In addition, when the target is in the flight axis direction of the mounted machine, if the rotational movement of the rigid target is small, the Doppler of the target reflection point in the cross range direction, such as left and right and up and down, will be the same, so the true target shape There is a problem that the shapes of the SAR image and the SAR image are greatly different and cannot be identified.

  Further, when the synthetic aperture length is short, there is a problem that the absolute position accuracy of the image cell is low even if the rotational motion of the rigid target is small.

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) Far field range, IEICE, Revised radar technology, pp.144-145 (1996)

JP 2008-304321 A

  As described above, in the ISAR processing applied to the conventional radar apparatus, the shape and size of the generated image are true target shapes when the relative velocity between the radar observation position and each of the target multiple reflection points is different. There was a problem that it was greatly different from the dimensions. Along with this problem, target identification ability and position observation ability of a specific point within the target are reduced, and in Doppler radar etc., the glint noise becomes large and the angle measurement accuracy is also reduced. When there is a target in the flight axis direction of the observable aircraft, the true target shape and the shape of the SAR image are very different and cannot be distinguished. When the synthetic aperture length is short, the rotational motion of the rigid target is small. However, there is a problem that the absolute position accuracy of the image cell is low.

  The present embodiment has been made in view of the above problems, and a radar apparatus capable of generating an image close to the true target shape and dimensions even when the relative speeds of the radar and the target multiple reflection points are different. An object of the present invention is to provide a radar signal processing method. Furthermore, the flight axis direction of the aircraft that can detect the target position by measuring the angle with high accuracy by reducing the glint noise in the Doppler radar etc. A radar apparatus and a radar signal capable of generating a SAR image close to the target shape even when the target is present and obtaining a SAR image with high absolute position accuracy even when the rotational motion of the rigid target is small and the synthetic aperture length is small An object is to provide a processing method.

  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 the ISAR (Inverse Synthetic Aperture Radar) type radar apparatus that images the target on the range-Doppler frequency axis, the beam generation means outputs a monopulse from the received signal of the real aperture antenna. A beam of Σ, ΔAZ, and ΔEL is generated and sampled and output, and a range-Doppler image in the range-Doppler frequency axis is generated from the sampling output of the beams of Σ, ΔAZ, and ΔEL by the image generation means, and a target image is generated. The extraction means extracts a predetermined target image from the range-Doppler image of the Σ beam. The position of the Doppler-range cell of the target image is extracted based on the range of the Σ beam and the monopulse angle measurement value of the Σ, ΔAZ, and ΔEL beams for the extracted target image. To obtain a target 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 narrow-band processor 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 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 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 block diagram which shows the structure of the radar apparatus which concerns on 2nd Embodiment. The conceptual diagram for demonstrating the outline | summary of the ISAR process in a synthetic aperture in the radar apparatus shown in FIG. The conceptual diagram which shows the curve characteristic of the cone of a beam in the radar apparatus shown in FIG. The block diagram which shows the structure of the radar apparatus which concerns on 3rd Embodiment. The figure for demonstrating the sample method in the radar apparatus shown in FIG. The block diagram which shows the structure of the radar apparatus which concerns on 4th Embodiment. (A) shows the extent of the beam width of ranges 1 to N, and (b) is a diagram showing the relationship between the error voltage of ranges 1 to N and the target range.

  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 transmission / reception unit 21 generates a Σ signal, a ΔAZ signal, and a ΔEL signal and outputs them to the signal processor 3.

  The Σ signal, ΔAZ signal, and ΔEL signal input to the signal processor 3 are converted into digital signals for each system by AD (Analog-Digital) conversion units 311, 312, and 313 in each system, and narrowband processing unit 32. The narrowband processing unit 32 calculates the angle of the target direction from the input Σ signal, ΔAZ signal, and ΔEL signal. The measured angle values (Σ, ΔAZ, ΔEL) obtained here are sent to the beam controller 22.

  FIG. 2 shows a specific configuration of the narrowband processing unit 32. In FIG. 2, the digitized Σ signal, ΔAZ signal, and ΔEL signal are sent to the data extraction units 3211 to 213 in each system. In order to reduce the sampling rate and reduce the processing scale, the data extraction units 3211 to 3213 pass the input Σ signal, ΔAZ signal, and ΔEL signal through a predetermined frequency filter, and then within a PRI (Pulse repetition Interval) Acquire data by range cell. The range cell signals of Σ, ΔAZ, and ΔEL obtained by the data extraction units 3211 to 213 are converted into PRI axis frequency domain signals by the PRI axis FFT (Fast Fourier Transformation) processing units 3221 to 223, and then the range ( Time) Pulse compression is performed on the range axis by the compression units 3231 to 233 to form a range compressed signal.

  Among them, the Σ-system range compressed signal is sent to a CFAR (Constant False Alarm Rate) processing unit 324, and a range cell having a plurality of extreme values is detected by the CFAR processing. For the range cell detected here, the threshold detection unit 325 detects a range cell having an extreme value equal to or greater than the threshold 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 3261 and 3262, respectively, and a range cell signal corresponding to the range cell detected by the threshold detection unit 325 of the Σ system is extracted, and the Σ Together with the signal of the detection cell of the system, it is sent to the angle measuring unit 327, where angle measurement in the target direction is performed.

  On the other hand, the received signal of the Σ system digitized by the AD conversion unit 311 is sent to the data extraction unit 33. The data extraction unit 33 observes the Doppler range of a 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 data extracted here is converted into a frequency domain signal of the PRI axis for each CPI (Coherent Processing Interval) by the PRI axis FFT processing unit 34, and is pulse-compressed on the range axis by the range compression unit 35. This pulse compression signal is sent to the CFAR processing unit 36, and a range cell having a plurality of extreme values is detected by the CFAR processing. For the range cell detected here, the threshold detection unit 37 detects a range cell having an extreme value equal to or greater than a threshold value. The range / Doppler calculation unit 38 calculates a target range and Doppler frequency for each CPI from the signal of the range cell detected by the threshold detection unit 37. The reference signal generation unit 39 generates a reference signal for pulse compression from the range and Doppler frequency detected for each CPI.

  The received signals of Σ, ΔAZ, and ΔEL digitized by the AD conversion units 311 to 313 are passed through predetermined frequency filters for satisfying the sampling frequency in the data extraction units 3A1, 3A2, and 3A3. . Then, range compression is performed by the range compression units 3B1, 3B2, and 3B3, and further, cross-range compression (AZ compression) is performed based on the reference signal by the AZ compression units 3C1, 3C2, and 3C3, and then the imaging unit 3D1 by polar format conversion is performed. Sent to 3D2 and 3D3. The imaging units 3D1, 3D2, and 3D3 convert the received signals subjected to range / cross-range compression into frequency domain signals by two-dimensional FFT processing, perform image processing by polar format conversion, and perform two-dimensional inverse FFT processing. Thus, the signal is converted back to the time domain and imaged. Note that the imaging units 3D1, 3D2, and 3D3 may be used to improve image quality and can be omitted.

  Thereafter, in the Σ system, the cell selection unit 3E selects a cell whose amplitude exceeds a predetermined threshold among the images generated by the imaging units 3D1, 3D2, and 3D3. In the ΔAZ, ΔEL system, the cells selected by the cell selection unit 3E are notified to the cell extraction units 3F1, 3F2, and cells of ΔAZ, ΔEL corresponding to the selected cells are extracted. The angle measuring unit 3G measures the target direction from the Σ, ΔAZ, and ΔEL cell signals obtained by the cell selecting unit 3E and the cell extracting units 3F1 and 3F2, and the imaging unit 3H measures the angle by the angle measuring unit 3G. The target is imaged and output.

  In the radar apparatus having the above configuration, the ISAR process will be described below with reference to FIGS.

  First, the outline of the synthetic aperture of the radar apparatus will be described with reference to FIG. In a radar device mounted on a flying object, a pulse is transmitted at a PRI (Pulse Repetition Interval) interval within a synthetic aperture time (1 cycle) and a reflected wave is received so that the target is always irradiated with a real aperture beam. For each pulse, data in the PRI is acquired in units of range cells. Using this acquired data, an ISAR process is performed to obtain a target ISAR image. Although FIG. 3 shows the case of a radar apparatus mounted on a flying object, the radar apparatus may be fixed if an ISAR image can be obtained.

  In FIG. 1, the beam control unit 22 directs a beam to a range to be imaged and transmits / receives the received signal, and the received signal is divided into systems of Σ, ΔAZ, and ΔEL and converted into a digital signal. The beam directing direction is the direction in which the narrow band processing unit 32 measures the target direction. For this angle measurement, the result of broadband monopulse angle measurement may be used without using narrowband processing.

  As shown in FIG. 2, the narrowband processing unit 32 receives AD conversion outputs of Σ, ΔAZ, and ΔEL of the system shown in FIG. 1, and the data extraction units 3211 to 213 reduce the sampling rate to reduce the processing scale. Therefore, sampling is performed after a predetermined band is extracted by the frequency filter. Among them, the Σ system signal is converted into a PRI-axis frequency domain signal by the PRI-axis FFT processing unit 34, pulse-compressed in the range direction by the range compression unit 35, and a range cell having a plurality of extreme values is converted by the CFAR processing unit 36. Then, the range detection unit 37 detects a range cell having an extreme value greater than or equal to the threshold value. The cells of ΔAZ and ΔEL corresponding to the detected cells are extracted by the cell extraction units 3261 and 3262, and the angle measuring unit 327 performs angle measurement using the Σ, ΔAZ, and ΔEL signals. Using this angle measurement value, the beam controller 22 in FIG. 1 directs the beam in the target direction.

Next, necessary sample data is extracted by the Σ-system data extraction unit 33 of FIG. In the data extraction 33, a Doppler range of a representative point such as a target center of gravity is observed, and a reference signal for AZ compression is generated based on Doppler range information when the beam is directed in the target direction. Extract data. That is, as shown in FIG. 4, N hit PRI data including duplicates is extracted from PRI1 to PRIN from the data Nall acquired for the synthetic aperture. Here, assuming CPI (m) (m = 1 to M), the PRI axis FFT processing unit 34 converts each CPI into a PRI axis frequency domain signal, the range compression unit 35 performs pulse compression in the range direction, and CFAR. A cell having a plurality of extreme values is detected by the processing unit 36, a cell having an extreme value equal to or higher than the threshold is detected by the threshold detection unit 37, and a target range and Doppler frequency are calculated by the range / Doppler calculation unit 38. Next, the reference signal generation unit 39 calculates an approximate curve of the reference signal Ref shown in FIG. 5 based on the range and Doppler frequency calculated for each CPI. This is formulated as follows.

  On the other hand, the monopulse outputs Σ, ΔAZ, and ΔEL of the antenna 1 are converted into digital signals by the AD conversion units 311, 312, and 313, sampled and output by the data extraction units 3 A 1, 3 A 2, and 3 A 3, respectively, and the range compression units 3 B 1, 3 B 1 After the correlation calculation with the reference signal for range compression corresponding to the waveform of the modulation signal is performed by 3B2 and 3B3, the AZ compression is performed by the correlation calculation with the reference signal generated by the expression (1) in the AZ compression units 3C1, 3C2, and 3C3 Is done. 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 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 obtain a signal on the time axis, the s may be subjected to inverse Fourier transform. However, in order to perform cross range compression (AZ compression, see Non-Patent Document 3), the (ω, u) axis of the signal s Leave as it is. Next, cross range compression is performed, and the reference signal uses the equation (1), and the same value is input for the ω axis.

The signal cs is obtained by multiplying the equation (5) and the equation (6-3).

Using this, FFT processing is performed on the u axis to obtain a frequency domain signal fcs (ω, ku).

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

  Next, as a more accurate image generation method, SAR image processing of the imaging units 3D1, 3D2, and 3D3 by polar format conversion will be described with reference to FIGS. 6 and 7 (see Non-Patent Document 4).

FIG. 6 shows a procedure for acquiring a SAR image by the radar apparatus according to the first embodiment. First, sample point data u of the synthetic aperture length with respect to the sampling time t is taken in as an input signal sig (t, u) (S11), and Fourier transform (FFTx (ω, u)) with respect to the t-axis is performed (S12). As a result, the range compression is performed by multiplying Sin (ω, u) by the result of Fourier transform (FFTx (ω, u)) with respect to the t-axis of the reference signal (S13), and an output s of the range compression is obtained. Using this range compression signal s, Fourier transform is performed with respect to the u-axis (S14).

Next, a reference signal for AZ compression is generated.

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

For the image center, the range, Doppler, and angle are observed and set as the position calculated by the following equation.

Here, the observation distance, the observation AZ angle, and the observation EL angle may be, for example, the average value of the observation values at each CPI in FIG.

Using this AZ compression reference signal, fsm is calculated by the following equation (S15).

Polar format conversion shown in FIG. 7 is performed using fsm, and lattice point data F (kx, ky) is generated on the kx axis and ky axis (S16). Polar format conversion is a method of calculating the interpolated data of the (kx, ky) axis grid points using the acquired data using an interpolation method, etc., and details are omitted as in Non-Patent Document 4. To do. Using this fsm, an image fsar using polar format conversion is output by two-dimensional inverse FFT (S17).

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

Next, using the Σ-system image output, cells whose amplitude exceeds a predetermined threshold in an XY axis image (corresponding to a Doppler range axis when polar format conversion is not used) (P cells) Is selected. The ΔAZ and ΔEL image output cells corresponding to each of the P cells are extracted by the cell extraction units 3F1 and 3F2, and the angle measurement unit 3G uses Σ, ΔAZ, and ΔEL cell signals (complex signals). Then, monopulse angle measurement is performed (see Non-Patent Document 5). Using this angle measurement value and distance, the imaging unit 3H forms an image according to the following equation.

The state of this image conversion is shown in FIG. In FIG. 8, (a) is a range-Doppler image, and (b) is a converted image obtained by performing coordinate conversion using the range / angle-measured value of the image of (a). As is apparent from FIG. 8, an image close to the true value position can be generated by coordinate conversion based on the range / angle measurement value.

  According to the method of the first embodiment, there is a target in the flight direction of the mounted machine, the target has no rotational motion, has ambiguity in the cross range direction, and the SAR image has the actual target shape. Even if they differ greatly, the angle of measurement of the actual aperture can be distinguished in the cross-range direction, so that an image close to the actual shape can be obtained.

(Second Embodiment)
In the first embodiment, the angle measurement accuracy of the actual aperture may be low. The second embodiment describes a method for improving the angle measurement accuracy of the actual aperture.

  FIG. 9 is a block diagram showing a configuration of a radar apparatus according to the second embodiment. 9 is different from the configuration shown in FIG. 1 in that a ΔSAR weight multiplication unit 3I, an AZ compression unit 3C4, an imaging unit 3D4 by polar format conversion, and a cell extraction unit 3F3 are provided, and the angle measuring unit shown in FIG. Instead of 3G, a SAR angle measurement unit 3J, an actual aperture angle measurement unit 3K, and an angle measurement correlation unit 3L are provided.

  In the first embodiment, the monopulse angle measurement value of the real aperture antenna is used. However, in order to improve the angle measurement accuracy, a synthetic aperture as shown in FIG. 10 is used. That is, when the target is in the vicinity of the flight path axis, the beam is directed in the endfire direction of the linear array (the axial direction of the linear array) by the synthetic aperture. In this case, the synthetic aperture beam width is wider than when the beam is formed in the broad side direction (perpendicular to the axis of the linear array), but when the synthetic aperture length is large, it is larger than the beam width of the real aperture antenna. It becomes narrow enough. Monopulse measurement using the Σ signal, which is a sum signal using data of N samples for each PRI of this endfire array, and the Δ signal, which is a difference signal obtained by dividing the apertures 1 to N / 2 and N / 2 + 1 to N by two. A corner (see Non-Patent Document 5) is performed. Thereby, the SAR angle measurement value is obtained (see Patent Document 1).

  This beam is a conical beam as shown in FIGS. 10 and 11 centering on the axis of the endfire array. If the target is in this conical shape, the position cannot be uniquely identified. For this countermeasure, the monopulse angle measurement value (AZ angle and EL angle) of the real aperture antenna is used as in the first embodiment. Specifically, the conical curve of the beam shown in FIG. 10 is drawn by the target distance R and the SAR angle measurement value θSAR by the endfire, and the conical shape closest to the target position by the real aperture antenna determined by the equation (16) is drawn. A point may be extracted and replaced with the conversion position of the first embodiment.

The above processing will be described with reference to the system diagram shown in FIG. A description of the same parts as those in the first embodiment will be omitted. Of the outputs of the Σ signal that have been subjected to range compression by the range compression unit 3B1, a signal for reducing the side lobe for the Δ signal is multiplied by the ΔSAR weight multiplication unit 3I with respect to the signal divided into two apertures as described above, and AZ The compression unit 3C4 and the polar format conversion imaging unit 3D1 perform AZ compression and polar format conversion, respectively, to form an image. Further, the cell selection unit 3E notifies the cell extraction unit 3F3 of the cell selected, and extracts the ΔSAR signal corresponding to the selected cell of Σ. Using the Σ and ΔSAR signals thus obtained, an error voltage ε of the following equation is calculated.

  If the angle measuring unit 3G measures the angle by comparing the error voltage ε with an error voltage table created in advance, a conical angle can be calculated. Using this SAR angle measurement value, a highly accurate target position may be calculated by the above-described processing.

As for SAR angle measurement, the case of phase monopulse angle measurement using Σ and Δsar signals has been described. However, instead of the Δsar signal, Σ2sar beam obtained by dividing the Σ signal beam by the squint angle may be used for squint angle measurement. Needless to say, it is good. In this case, the error voltage ε is as follows.

The angle can be measured using this error voltage ε and a previously created error voltage table. Further, the angle can be measured even in the case of an amplitude monopulse using only the amplitude (see Non-Patent Document 6).

  Using the angle measurement value and the distance, the imaging unit 3H images the three-dimensional position according to equation (16). Thereby, according to 2nd Embodiment, even when a target exists in the vicinity of a flight path axis | shaft, the angle measurement precision of a real opening can be improved and the image close | similar to a true value can be acquired.

  In the second embodiment, the gist of the monopulse angle measurement method in which the synthetic aperture length is divided into two apertures has been described. However, this is a method that uses the FFT of the sample sequence within the synthetic aperture length, and is based on the Doppler frequency axis. It can also be said to be a monopulse technique. As a result, when the rotational motion of the rigid target is large, a phase error due to the Doppler frequency component occurs, so that the angle measurement value also has an error in the same manner as the image is distorted in the cross range direction. Therefore, the conditions for improving the absolute position accuracy with this method are when the rotational motion of the rigid target is low, or when the rotational motion of the rigid target is observed and the phase component due to the Doppler can be corrected. As much as is used, the accuracy of the cross range is improved.

(Third embodiment)
In the first embodiment and the second embodiment, ΔAZ and ΔEL systems are required in addition to Σ, and the processing scale increases. In the third embodiment, each of the Σ, ΔAZ, and ΔEL systems is shared, and an increase in processing scale is suppressed.

  FIG. 12 is a block diagram showing a configuration of a radar apparatus according to the third embodiment, and FIG. 13 is a diagram for explaining a sampling method in the third embodiment. Description of the same parts as those in the first and second embodiments is omitted.

  In the first and second embodiments, three systems of Σ, ΔAZ, and ΔEL are simultaneously sampled. However, in the third embodiment, Σ, ΔAZ, and ΔEL obtained by the transmitter / receiver 21 in the transceiver 2. Each signal is sampled by the sample switching unit 23, and only one AD conversion unit 31 is used for AD conversion.

  That is, the sample switching unit 23 of the transceiver 2 switches each system to time division as shown in FIGS. 13 (a) and 13 (b). In this case, if the system for sampling three systems in order is sampled at the same time, a time difference is generated, and the angle error becomes large. For this countermeasure, the sampling order for the three systems is pseudo-randomized and thinned samples are implemented. In order to set the AD conversion unit to 1ch, in the transceiver 2, the sample switching unit 23 switches the order of the three systems from the transmission / reception unit 21 in a pseudo-random order. Subsequent processing is the same as in the first and second embodiments.

(Fourth embodiment)
The distance between the radar and the target may be a long distance or a short distance. In the first and second embodiments, the far field range (see Non-Patent Document 7) is satisfied, particularly in the short distance. Without, it is assumed that the beam width is widened. In this case, if the same angle measurement table as in the case of a long distance is used, the error voltage is not matched and an error occurs in the angle measurement value. In the fourth embodiment, this countermeasure is taken. FIG. 14 is a block diagram illustrating a configuration of a radar apparatus according to the fourth embodiment.

  As the angle measurement curve, generally, a far distance (range 1) that satisfies the far field condition has a narrow beam width, and a short distance that does not satisfy the far field condition (closer to the range N) has a wide beam width. This is shown in FIG. FIG. 15A shows the extent of the beam width in the ranges 1 to N, and FIG. 15B shows the relationship between the error voltage in the ranges 1 to N and the target range. As is apparent from FIG. 15, the angle measurement error voltage may be tabulated in advance from the Σ and Δ beams corresponding to the observation range, and the angle measurement table may be switched according to the observed target range.

  The fourth embodiment will be described with reference to the block diagram shown in FIG. As the angle measurement table, the SAR variable angle measurement unit 3M that observes the SAR angle measurement value based on the cells selected and extracted by the cell selection unit 3E and the cell extraction unit 3F3 of the Σ system, and the cell extraction of the ΔAZ and ΔEL systems, respectively. There is an actual aperture variable angle measuring unit 3N that performs variable angle measurement of the actual aperture based on the result, and each angle measuring unit 3M, 3N switches the table according to the range calculated by the range Doppler calculating unit 38 of the Σ system.

  In the first to fourth embodiments, the method of controlling the beam direction by the narrowband processing unit 32 in order to reduce the processing scale has been described. However, wideband processing (SAR processing) and other sensors are described. If the beam direction is known from the information from, etc., narrowband processing may not be performed.

  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, 23 ... Sample switching part, 3 ... Signal processor, 31, 311, 312, 313 ... AD converter, 32 ... Narrow band processing unit, 3211 to 2213 ... Data extraction unit, 3221 to 2223 ... PRI axis FFT processing unit, 3231 to 2233 ... Range (time) compression unit, 324 ... CFAR processing unit, 325 ... Threshold detection unit, 3261 3262 ... Cell detection unit, 327 ... Angle measurement unit, 33, 3A1, 3A2, 3A3 ... Data extraction unit, 34 ... PRI axis FFT processing unit, 35, 3B1, 3B2, 3B3 ... Range compression unit, 36 ... CFAR processing unit, 37: Threshold detection unit, 38: Range / Doppler calculation unit, 39: Reference signal generation unit, 3C1, 3C2, 3C3, 3C4 ... AZ compression 3D1, 3D2, 3D3, 3D4 ... Polar format conversion imaging unit, 3E ... cell selection unit, 3F1,3F2,3F3 ... cell extraction unit, 3G ... angle measuring unit, 3H ... imaging unit, 3I ... ΔSAR weight calculation 3J: SAR angle measuring unit, 3K: actual aperture angle measuring unit, 3L: angle measurement correlating unit, 3M: SAR variable angle measuring unit, 3N: actual aperture variable angle measuring 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,
Beam generating means for generating and sampling each beam of Σ, ΔAZ and ΔEL, which are monopulse outputs, from the received signal of the real aperture antenna;
Image generation means for generating a range-Doppler image on the range-Doppler frequency axis from the sampling outputs of the beams of Σ, ΔAZ, and ΔEL;
A target image extracting means for extracting a predetermined target image from the range-Doppler image of the Σ beam;
A target for obtaining a target image by calculating a position of a Doppler-range cell of the target image based on a range by the Σ beam and a monopulse angle value by the beams of Σ, ΔAZ, and ΔEL for the extracted target image. A radar apparatus comprising image acquisition means.   The target image acquisition means divides an arbitrary plurality of hits of CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna into two, and selects a Doppler-range cell by the sum signal ΣSAR by the Σ beam The cone angle θSAR is measured by monopulse processing using the ΣSAR corresponding to the selected cell and the difference signal ΔSAR by the Σ beam, and the angle of each of the above-mentioned ΔAZ and ΔEL beams among the measured cone angles θSAR is measured. The radar apparatus according to claim 1, wherein the position of the Doppler-range cell is calculated from angles θAZcal and θELcal close to values θAZ and θEL.   The beam generating means performs sampling output by switching the Σ beam, ΔAZ beam, and ΔEL beam in pseudo-random order within an arbitrary plurality of hits of CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna. The radar device according to claim 1 or 2.   The target image acquisition means divides an arbitrary plurality of hits of CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna into two, and outputs the first from the outputs of the Σ, ΔAZ, and ΔEL beams. The monopulse angle curve is calculated, the second monopulse angle curve is calculated from the sum signal ΣSAR by the Σ beam and the difference signal ΔSAR by the Σ beam, and is tabulated for each predetermined range range, and the observed target range The radar apparatus according to claim 1, wherein the first and second monopulse angle measurement curves are switched by calculating a Doppler-range cell position of the target image based on the switched monopulse angle measurement curves. 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,
Generate and output Σ, ΔAZ and ΔEL beams, which are monopulse outputs, from the received signal of the real aperture antenna,
A range-Doppler image in the range-Doppler frequency axis is generated from the sampling outputs of the beams of Σ, ΔAZ, and ΔEL,
A predetermined target image is extracted from the range-Doppler image of the Σ beam,
A radar that obtains a target image by calculating the position of a Doppler-range cell of the target image based on the extracted target image based on the range of the Σ beam and the monopulse angle value of the Σ, ΔAZ, and ΔEL beams. Signal processing method.   The target image is acquired by dividing a plurality of hits of CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna into two, and selecting a Doppler-range cell by the sum signal ΣSAR using the Σ beam. The cone angle θSAR is measured by monopulse processing using the ΣSAR corresponding to the selected cell and the difference signal ΔSAR by the Σ beam, and the angle of each of the above-mentioned ΔAZ and ΔEL beams among the measured cone angles θSAR is measured. The radar signal processing method according to claim 5, wherein the position of the Doppler-range cell is calculated based on angles θAZcal and θELcal close to the values θAZ and θEL.   The beam generation is performed by sampling and outputting the Σ beam, ΔAZ beam, and ΔEL beam in pseudo-random order within an arbitrary plurality of hits of the CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna. The radar signal processing method according to claim 5.   The acquisition of the target image is performed by dividing an arbitrary plurality of hits of CPI (Coherent Processing Interval) in the synthetic aperture length of the real aperture antenna into two and firstly outputting from the outputs of the beams of Σ, ΔAZ, and ΔEL. The monopulse angle curve is calculated, the second monopulse angle curve is calculated from the sum signal ΣSAR by the Σ beam and the difference signal ΔSAR by the Σ beam, and is tabulated for each predetermined range range, and the observed target range The radar signal processing method according to claim 5, wherein the first and second monopulse angle measurement curves are switched by calculating the position of the Doppler-range cell of the target image based on the switched monopulse angle measurement curves.

Images