JP2017161358A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve speed accuracy and heighten range-Doppler position and speed accuracy even when there is a change in target speed during image generation.SOLUTION: A radar device according to an embodiment of the present invention transmits/receives a transmission/reception signal of a non-modulated continuous wave or pulse wave by a real aperture antenna a number of times within a synthetic aperture time, and acquires the initial values of speed and, as necessary, acceleration. The radar device also transmits/receives a transmission/reception signal of a frequency-swept continuous wave or a pulse wave of step frequency by the real aperture antenna a number, and observes speed and, as necessary, acceleration by Doppler on a slow-time axis. Furthermore, the radar device generates a reference signal for cross range compression in a range of speed widths and acceleration widths given to acceleration as necessary, on the basis of the initial value of speed and of acceleration acquired as necessary and the observed speed and acceleration, generates a range-Doppler image using this reference signal, and outputs a range of the image amplitude of the range-Doppler image exceeding a prescribed threshold as a representative value.SELECTED DRAWING: Figure 1

Description

  The present embodiment relates to a radar apparatus that observes a target range and angle.

  In a conventional radar apparatus, there is a process called ISAR (Inverse Synthetic Aperture Radar) (see Non-Patent Document 1) as one method of observing a target range and angle. In this ISAR processing, the center of gravity of the target is tracked by both the range and Doppler axes to obtain the center of the image, and the target is imaged by the range-Doppler axis by performing range compression and AZ compression (cross range compression). .

  Here, in the conventional ISAR process, the following points are pointed out.

  First, in the ISAR process, in order to correct the image center of the range-Doppler axis, a reference signal for AZ compression is generated based on the position and speed of the target tracking data. There is a problem in that it is not possible to cope with this, and an error occurs in the reference signal, resulting in an error in the coordinate point of the range-Doppler axis.

  In addition, in the ISAR process, there is a problem that the cross range dimension of the generated image is different due to Doppler change due to rotation (vibration) of the observation target. That is, when a specific point within the target having a size is detected based on the ISAR image and the process of tracking this point is executed, the cross range is different from the absolute value, so that the error becomes large and tracking is performed. There was a problem that became difficult.

  The purpose of the ISAR processing is to generate an image of the range-Doppler axis, but it is not necessarily the purpose of imaging. The high resolution processing of the range-Doppler axis improves SN (signal power versus noise power) and the range. -It may be aimed at improving the resolution on the Doppler axis. In such a target radar, for example, a Doppler radar that does not generate an ISAR image, when measuring a target having a size, vector synthesis (complex synthesis) of a plurality of points with a wide angle measurement point is performed. There was a problem of increased noise.

  In the following description, even in the case of processing for generating an ISAR image by high-resolution processing of the range-Doppler axis, including high-resolution Doppler radar processing that is not necessarily the purpose of image generation, “ISAR processing” is used for simplicity. , “Range-Doppler image generation” or the like.

SAR method (ISAR: Inverse Synthetic Aperture Radar), 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) Phase monopulse (phase comparison monopulse) system, Yoshida, 'Revised radar technology', IEICE, pp.262-264 (1996) Amplitude monopulse (amplitude comparison monopulse) system, Yoshida, 'Revised radar technology', IEICE, pp. 260-262 (1996) Step frequency, Caner, ‘INVERSE SYSTHETIC APERTURE RADAR IMAGING WITH MATLAB ALGORITHMS’, A JOHN Willey & SONS, pp.239-241 (2012)

  As described above, in the conventional radar apparatus, in the ISAR processing, the generation of the reference image for AZ compression cannot correspond to the speed change at the time of image generation, and the generated image is caused by the Doppler change due to the rotation (vibration) of the observation target. However, there are problems that the cross range dimension is different and that the glint noise is increased by vector synthesis of a plurality of points.

  The present invention has been made to solve the above problem, and even when there is a target speed change during image generation, the speed accuracy can be improved, and the position and speed accuracy of the range-Doppler axis can be increased. Radar that can improve the accuracy of the cross range (angle) and reduce the glint noise due to multiple reflection points even when there is a problem that the cross range size of the generated image differs due to the influence of Doppler change due to rotation (vibration) of the An object is to provide an apparatus.

  According to the embodiment, in a radar apparatus that observes a target range and angle using a real aperture antenna, a transmission / reception signal of an unmodulated continuous wave or pulse wave is transmitted by the real aperture antenna within the synthetic aperture time (Ncw (Ncw ≧ 1)). ) Transmit and receive times, obtain initial values of speed and acceleration as necessary, send and receive signals transmitted and received by continuous wave or stepped pulse wave with frequency sweep by real aperture antenna, speed and Doppler of slow-time axis Acceleration is observed as necessary, and based on the initial value of the speed and acceleration acquired as necessary, and the observed speed and acceleration, the speed range (Nv, Nv ≧ 1) and as necessary Generates a reference signal Np (Np = Nv × Na) for cross-range compression in a range where acceleration has an acceleration width (Na street, Na ≧ 0), and generates a range-Doppler image using this reference signal The range - the image amplitude of the Doppler image and outputs the range exceeds a predetermined threshold as the representative value.

The block diagram which shows the structure of the whole system | strain of the radar apparatus which concerns on 1st Embodiment. The figure for demonstrating the outline | summary of the ISAR process of the radar apparatus shown in FIG. The figure for demonstrating the 1st Example of the transmission pulse of the radar apparatus shown in FIG. The figure which shows a mode that the representative value of a speed and an acceleration is calculated with the transmission pulse of the radar apparatus shown in FIG. The figure for demonstrating the 2nd Example of the transmission pulse of the radar apparatus shown in FIG. The figure for demonstrating the 3rd Example of the transmission pulse of the radar apparatus shown in FIG. The figure which shows the ranging value of the target image and representative point by the range-cross range (Doppler) of the radar apparatus shown in FIG. The block diagram which shows the structure of the whole system | strain of the radar apparatus which concerns on 2nd Embodiment. The figure for demonstrating the angle detection of the target by the beam of the sum ((SIGMA)) of a radar apparatus shown in FIG. 8, and a difference ((DELTA)). The figure which shows the ranging value of the target image and representative point by the range-cross range (Doppler) of the radar apparatus shown in FIG. The block diagram which shows the structure of the whole system | strain of the radar apparatus which concerns on 3rd Embodiment. In the radar apparatus shown in FIG. 11, the figure which compares and shows the case of a simultaneous sample, and the case of a thinning sample.

  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. In the following description, it is assumed that the embodiment of the antenna device is applied to a radar device.

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

  FIG. 1 shows a system of a radar apparatus according to this embodiment, and FIG. 2 shows an outline of ISAR processing. Here, as shown in FIG. 2, the beam is directed so as to always irradiate the target with an actual aperture beam by the on-board radar, and is transmitted with PRI (Pulse Repetition Interval) within the synthetic aperture time (one cycle). For each pulse, data is acquired in units of range cells in the PRI. Using this acquired data, ISAR processing is performed to obtain range-Doppler data (hereinafter referred to as RD data). Although FIG. 2 is a diagram in the case of an on-board radar, a fixed radar may be used as long as RD data can be obtained.

  As shown in FIG. 1, the system of the radar apparatus according to the present embodiment includes an antenna 1, a transceiver 2, and a signal processor 3. In the transceiver 2, a CW (continuous wave or pulse) unmodulated signal generated by the transceiver 21 is transmitted as a transmission signal from the antenna 1, and a reflected wave signal received by the antenna 1 is received. At this time, the beam control unit 22 controls the directivity direction and spread of the transmission / reception beam to direct the RD data to a range where it is desired to be generated.

  In the signal processor 3, the received signal obtained by the transceiver 2 is converted into a digital signal by the AD converter 31 and then distributed to three systems.

In the first system, a digital signal obtained by transmitting and receiving a non-modulated signal of the CW signal (continuous wave or pulse) shown in FIG. 3A is sampled by the data extraction unit 32, and HPRF (High-PRF: High pulse repetition frequency) -FFT processing unit 33 performs fast-time axis FFT processing to observe the Doppler frequency, and CFAR (Constant False Alarm Rate) processing unit 34 performs CFAR detection for speed extraction. The unit 35 calculates the relative speed Vcw of the CFAR detection signal by the following equation.

  At this time, the PRF is selected so that the maximum value of the target relative speed can be measured without ambiguity. This CW signal is inserted into the synthetic aperture transmission / reception signal multiple times (Ncw) in consideration of the speed change within the synthetic aperture time (# 1 to #N), and the average velocity value (Vcwave), etc. May be used.

  When inserting, the insertion interval is pseudo-randomized and inserted as shown in FIG. 3A so that the grating lobe of the cross-range axis of the range-Doppler data at the time of the synthetic aperture is within the allowable range. To do. At this time, as shown in FIG. 4A, since the speed with respect to time can be observed, the acceleration Acw can also be calculated from the speed gradient.

  On the other hand, in the second system, the digital signal obtained by transmitting and receiving the chirp modulated signals # 1 to #N shown in FIG. 3B is sampled by the data extraction unit 36, and the PRI axis FFT processing unit 37 is sampled. The Doppler velocity is calculated by FFT of the slow-time axis in the PRI axis direction. Then, after compression corresponding to the waveform of the modulation signal is performed in the range axis direction by the range compression unit 38, a representative point such as a target center of gravity is detected by the CFAR processing unit 39, and the velocity Vd is calculated by the range / Doppler calculation unit 3A. To do.

Here, the Doppler speed calculated from the slow-time axis FFT of the PRI axis FFT processing unit 37 may have ambiguity when the relative speed is high. For this reason, the speed Vcw calculated by the non-modulated signal processing of the speed extraction unit 35 is used to calculate the speed with the ambiguity corrected by the speed calculation unit 3B.

As this speed, the transmission / reception signals of the synthetic aperture times of # 1 to #N in FIG. 3B are divided into M ways, and the above-described equations (1) to (1) to The speed Vsar1 to VsarM having no ambiguity is calculated using (3), and the speed Vsar such as the average value is calculated. This is shown in FIG. From this velocity gradient, the acceleration Asar can also be calculated.

Based on the velocity Vcw and acceleration Acw calculated from the CW signal and the velocity Vsar and acceleration Asar calculated by observation for the synthetic aperture, the representative velocity Vc and the representative acceleration Ac used in the reference signal are calculated from the representative values such as the average values. be able to.

  The above transmission / reception processing can be applied to the case where the transmission / reception signal of the SAR processing is the step frequency (FIGS. 5A and 5B) and the case of continuous wave sweep (FIGS. 6A and 6B). In the above description, the CW pulse (HPRF) is used as an unmodulated signal, but a continuous wave CW signal may be used.

  Next, the reference signal generation unit 3C generates a reference signal based on the representative speed and the representative acceleration, and generates RD data using the corrected reference signal. This is formulated as follows. As the transmission modulation signal, there is chirp modulation (see Non-Patent Document 2) shown in FIG. 3B as a pulse wave. FIG. 5 shows a step frequency method (see Non-Patent Document 6) in which the frequency is changed stepwise on the fast-time axis as a pulse wave and repeated on the slow-time axis. As a continuous wave, as shown in FIG. 6, there is a method of repeating a frequency sweep signal along a slow-time axis. Here, the case of chirp modulation of pulse modulation will be described.

In the third system, the digital signal obtained by transmitting and receiving the chirp modulated signals # 1 to #N shown in FIG. 5B is sampled by the data extraction unit 3D, and the input signal is input by the range compression unit 3E. And the range compression signal are correlated. In order to formulate the case where this is performed in the frequency domain, the input signal is set to the frequency axis (fast-time).

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.

This is subjected to FFT to obtain a frequency axis reference signal Sref (ω).

Next, as the processing of the Az compression unit 3F (see Non-Patent Document 3), the generation of the reference signal for Az compression in the reference signal generation unit 3C is formulated. As a reference signal, a plurality of reference signals are set based on a predetermined speed width and a predetermined acceleration width based on the speed of equation (2).

The correction signal of equation (9) is Nr = Nv × Na.
For the image center, the range, Doppler, and angle are observed and set as the position calculated by the following equation.

  Although the case where the velocity component is Vy is described as correcting Yc in equation (10), if the Vx and Vz components are known, they may be reflected in the components of Xc and Zc in equation (10), respectively. Here, when there are a plurality of reflection points, the observation AZ angle and the observation EL angle may be the average value of the observation values, for example.

Therefore, using the input signal (5), the reference signal (8) for range compression, and the reference signal (9) for Az compression, signals on the frequency axis of range compression and Az compression are expressed by the following equations.

Thereby, range-Doppler data (RD data) can be obtained by the following equation.

  As this RD data, data for a plurality of reference signals Np is generated. Among these RD data, a representative value such as an average value of amplitudes at points exceeding a predetermined amplitude threshold is calculated, and the RD data having the maximum value is selected by the data selection unit 3G. Using this RD data, a point that exceeds a predetermined threshold is selected by the cell selection unit 3H, and the distance and speed are calculated and output from the range and Doppler speed by the speed distance output unit 3I.

  This is shown in FIG. FIG. 7A shows an image and a representative point on the range-cross range axis, and FIG. 7B shows the frequency of the representative point on the distance measurement value. The speed is the result of the equation (2) used for the calculation of the reference signal, and the distance may be a representative value such as a median value in the histogram as shown in FIG. In addition, representative points such as an average value and a mode value may be used.

  As described above, in the present embodiment, an unmodulated continuous wave or pulse wave is transmitted / received Ncw (Ncw ≧ 1) times within the synthetic aperture time, and the initial value of acceleration and acceleration is obtained as necessary. Next, with respect to a transmission / reception signal using a frequency wave-swept continuous wave or a pulse wave having a step frequency, the velocity V and acceleration as required are observed by a slow-time axis Doppler. Then, based on the initial value and the velocity V and acceleration corrected by observation, a predetermined velocity width (Nv, Nv ≧ 1) and a predetermined acceleration width (Na, Na A reference signal Np (Np = Nv × Na) for cross-range compression in a range with ≧ 0) is generated, and a range Doppler image is generated using this reference signal. Finally, representative values such as a median value, an average value, and a mode value in a range where the image amplitude exceeds a predetermined threshold are output.

  According to this configuration, the speed without ambiguity is observed by the non-modulated signal, and the speed is corrected to the speed obtained from the slow-time Doppler speed using the speed as an initial value. At the same time, it can be corrected at the reference speed corresponding to the speed change at the time of RD data generation, and the RD data is obtained while reducing the processing scale, and the range is calculated with high accuracy by ranging using a high resolution range cell. can do.

  The above has described the case of a chirp signal with a pulse wave. This method suppresses the speed ambiguity and corrects the speed based on the speed observed by the unmodulated transmission / reception signal and the speed of the slow-time axis in the synthetic aperture time. Furthermore, in order to suppress the speed error, the speed and acceleration with a predetermined width are set around the correction value, and the representative point is based on the reference signal for Np cross-range compression (Az compression). Select the reference signal with the maximum amplitude. Accordingly, other modulation methods such as a continuous sweep signal and a step frequency of pulse modulation may be used.

(Second Embodiment)
In the first embodiment, the processing for calculating the distance and the speed has been described. In the second embodiment, processing for outputting an angle will be described.

  The system configuration is shown in FIG. In the first embodiment, only the Σ signal of the real aperture antenna is used. However, in this embodiment, ΔAZ and ΔEL (hereinafter referred to as Δ and Δ), which are difference signals between the AZ axis and the EL axis obtained by dividing the aperture of the real aperture antenna into two. (Describe).

  First, for Σ, RD data is obtained using the transmission modulation signals (# 0, # 1 to N) of FIG. 3 as in the first embodiment. For Δ, RD data is generated using a reference signal using the same speed as Σ by using # 1 to N of the transmission signal in FIG. 3 excluding the unmodulated signal. That is, for ΔAZ, RD data is obtained by the AD conversion unit 3J, the data extraction unit 3K, the range compression unit 3L, and the Az compression unit 3M. For ΔEL, RD data is obtained by the AD conversion unit 3O, the data extraction unit 3P, the range compression unit 3Q, and the Az compression unit 3R.

Next, cells exceeding a predetermined threshold are selected by the cell selection unit 3H using the RD data by Σ. Next, in the RD data of Δ, the cell extraction units 3N and 3S extract the same cells as the range-Doppler selected by the processing of Σ. Using the Σ, Δ (ΔAZ and ΔEL) signals of the extracted cells, the angle measuring unit 3T measures the angle. For phase monopulse angle measurement (see Non-Patent Document 4), an error voltage ε of the following equation is calculated.

By comparing this error voltage ε with a previously created error voltage table, as shown in FIGS. 9A and 9B, the angle can be measured by detecting the target angle using the sum (Σ) and difference (Δ) beams. .

As for SAR angle measurement, the case of phase monopulse angle measurement based on Σ and Δ signals has been described. However, instead of the Δ signal, Σ2 beam obtained by shifting the Σ signal beam by the squint angle may be used to perform squint angle measurement. Good. In this case, the error voltage is as follows.

The angle can be measured using this error voltage 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 5).

  Using the angle measurement value, as shown in FIG. 10, the representative point of the angle measurement value is output from the target image by the range-cross range (Doppler) and the distance measurement value of the representative point. The distance and speed are calculated and output by the speed distance angle output unit 3U as in the first embodiment.

  As described above, in the radar apparatus according to the second embodiment, a range Doppler image is generated based on the reference signal calculated according to the first embodiment, and the Σ beam and ΔAZ that are monopulse outputs of the real aperture antenna are generated. And ΔEL images are generated, the range Doppler cells exceeding the specified threshold are extracted from the RD data of Σ beam, and the range of each cell by Σ beam and the monopulse angle measurement value by Σ, ΔAZ and ΔEL beam are output. , Representative values such as the median value, average value, and mode value are output.

  According to this configuration, each position of each target having a size is calculated by calculating the position using the monopulse angle measurement value and the range of the real aperture antenna of the output of each cell obtained by separating the target image with the cell of the range-Doppler axis. The position angle (cross range) can be observed with high accuracy.

(Third embodiment)
In the second embodiment, ΔAZ and ΔEL systems are required in addition to Σ, which increases the processing scale. This countermeasure will be described in this embodiment. The system is shown in FIG. 11, and the processing contents are shown in FIG. In the second embodiment, three channels of Σ, ΔAZ, and ΔEL are sampled at the same time. However, as shown in FIG. 11, the sample switching unit 23 is provided in the transmitter / receiver 2 with AD conversion as one channel, and this sample The switching unit 23 switches the beam output in a time division manner, for example, within a CPI (Coherent Processing Interval: N hit) of the synthetic aperture length.

  In this case, if the method of sampling 3 channels in order is used, a time difference is generated, so that the angle error becomes large. For this measure, the sampling order for 3ch is pseudo-randomized and thinned samples are implemented. In order to set the AD conversion to 1ch, the sample switching unit 23 in FIG. 11 switches the order of 3ch from the transmission / reception unit 21 in pseudo-random order. Subsequent processing is the same as that of the second embodiment, and is omitted.

  As described above, in the radar apparatus according to the third embodiment, the Σ beam, which is the monopulse output of the real aperture antenna, and ΔAZ and ΔEL are combined based on the reference signal calculated by the method of the second embodiment. Performed within CPI (Coherent Processing Interval: N hit) of aperture length, sampled by switching Σ, ΔAZ, and ΔEL in the order of predetermined pseudo-random, and using the output, the median value and average of angle measurement value A representative value such as a value is output.

  According to the radar apparatus having the above-described configuration, by switching the Σ, ΔAZ, and ΔEL of the real aperture antenna to sample and input signals, the processing scale of the three systems is reduced, and the angle of each target position having a size Can be observed with high accuracy.

  In the RD data generation process (ISAR process), the case of a chirp signal has been described as shown in FIG. 3, but a step frequency method (in which the frequency band of a CW signal not subjected to chirp modulation is changed by changing the frequency for each PRI (see FIG. 3). Non-Patent Document 6, FIG. 5) or a continuous wave sweep signal (FIG. 6) may be used.

  In addition, the said embodiment is not limited as it is, In the implementation stage, a component can be deform | transformed and embodied in the range which does not deviate from the summary. 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.

1 ... antenna,
2 ... transceiver, 21 ... transceiver, 22 ... beam controller, 23 ... sample switching unit,
DESCRIPTION OF SYMBOLS 3 ... Signal processor, 31 ... AD conversion part, 32 ... Data extraction part, 33 ... HPRF-FFT processing part, 34 ... CFAR processing part, 35 ... Speed extraction part, 36 ... Data extraction part, 37 ... PRI axis FFT process Unit, 38 ... range compression unit, 39 ... CFAR processing unit, 3A ... range / Doppler calculation unit, 3B ... speed calculation unit, 3C ... reference signal generation unit, 3D ... data extraction unit, 3E ... range compression unit, 3F ... Az Compression unit, 3G ... data selection unit, 3H ... cell selection unit, 3I ... speed distance output unit, 3J ... AD conversion unit, 3K ... data extraction unit, 3L ... range compression unit, 3M ... Az compression unit, 3N ... cell extraction Part, 3O ... AD conversion part, 3P ... data extraction part, 3Q ... range compression part, 3R ... Az compression part, 3S ... cell extraction part, 3T ... angle measurement part, 3U ... speed distance angle output part.

Claims (5)

In a radar device that observes a target range and angle using a real aperture antenna,
An initial value acquisition means for transmitting and receiving an unmodulated continuous wave or pulse wave transmission / reception signal by a real aperture antenna Ncw (Ncw ≧ 1) times within the synthetic aperture time, and acquiring an initial value of acceleration as required,
An observation means for transmitting / receiving a transmission / reception signal using a continuous wave or a stepped pulse wave having a frequency sweep by a real aperture antenna, and observing the speed and acceleration as required by a slow-time axis Doppler,
Based on the initial value of the speed and the acceleration acquired as necessary, and the observed speed and acceleration, the speed width (Nv, Nv ≧ 1) and, if necessary, the acceleration width (Na, Na Data generation means for generating a reference signal Np (Np = Nv × Na) for cross-range compression in a range having ≧ 0) and generating range-Doppler data using this reference signal;
A radar apparatus comprising: output means for outputting a representative value of a range in which the amplitude of the range-Doppler data exceeds a predetermined threshold. The data generation means generates a cross-range compression reference signal for each of the Σ beam, ΔAZ, and ΔEL beam, which are monopulse outputs of the real aperture antenna, and uses range-Doppler data using the reference signal for each beam. Produces
The output means extracts a range-Doppler cell that exceeds a predetermined threshold in the range-Doppler data of the Σ beam, and represents the range of the extracted cell by the Σ beam and the monopulse angle measurement value by the Σ, ΔAZ, and ΔEL beams. The radar apparatus according to claim 1, which outputs a value.   In the Σ beam and ΔAZ and ΔEL that are monopulse outputs of the real aperture antenna, the observation means performs sampling by switching Σ, ΔAZ, and ΔEL in a predetermined pseudo-random order in a time division manner based on the reference signal. The radar apparatus according to claim 2.   The radar apparatus according to claim 3, wherein the observation unit performs switching between Σ, ΔAZ, and ΔEL within a CPI (Coherent Processing Interval: N hit) of a synthetic aperture length.   The radar apparatus according to claim 1, wherein the output unit outputs one of a median value, an average value, and a mode value as the representative value.

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