JP5251591B2 - Pulse compressor - Google Patents

Description

  The present invention relates to a pulse compression apparatus, and more particularly to a pulse compression apparatus in a radar apparatus that transmits a linear chirp pulse.

  Radar equipment emits radio waves into space and receives reflected signals from the target to detect the presence of the target and observe its position, motion state, etc. The main performance of the radar equipment is , Its detection ability, distance measurement accuracy, azimuth measurement accuracy and tracking performance.

  In a general radar apparatus, a radar reception signal is an analog signal, and is converted into a digital reception signal by performing AD conversion (analog to digital conversion), and then various signal processing is performed.

The purpose of signal processing in this case is to improve the signal-to-noise ratio (SNR), suppress reflected signals from the ground, sea surface, rain clouds, etc., and unwanted signals other than target signals such as interference waves. However, one of the typical processes is pulse compression.
Pulse compression is adopted as a technique to increase the detection capability of the radar device and improve the distance resolution while reducing the transmission peak power, and transmits a modulated transmission pulse. This is a processing method that achieves the above-mentioned object by correlating with a reference signal at the time of reception.

In the pulse compression technique, a chirp pulse is one of the methods widely used as a transmission pulse modulation method. The chirp pulse is a method of performing frequency modulation (FM) within a transmission pulse and transmitting it.
When performing pulse compression on the received signal, the peak amplitude value of the pulse compression waveform appears at the position corresponding to the distance where the target exists by performing correlation processing between the reference signal and the received signal. By detecting the value, the target distance can be measured simultaneously with the detection of the target signal.
The chirp pulse includes a linear chirp pulse whose modulation frequency changes linearly in the transmission pulse and a non-linear chirp pulse which does not change linearly.

As shown in the schematic diagram of FIG. 2, the linear chirp pulse is characterized in that the peak amplitude position after pulse compression is offset according to the line-of-sight direction velocity. This is because the frequency modulation in the received pulse is the target. This is because the transmission pulse changes depending on the Doppler frequency corresponding to the gaze direction velocity.
The offset distance ΔR of the pulse compression position is such that the transmission frequency is f (Hz), the transmission pulse width is τ (s), the phase dispersion bandwidth is Δf (Hz), the target speed is v (m / s), the target Doppler When the frequency is fd ((Hz) and the speed of light is c (m / s), it is expressed by the following calculation formula.
fd = 2 × v × f / c (1)
ΔR = (c / 2) × τ × fd × Δf (2)

As shown in equations (1) and (2), the magnitude of the distance offset is proportional to the target speed and the transmission pulse width.
In recent years, radar equipment has increased the transmission pulse width to cope with higher-speed missile detection and target detection at longer distances, in addition to dealing with the speedup of aircraft that has been the main detection target in the past. It is required to make it. For this reason, in a pulse compression type radar apparatus, the distance offset tends to increase due to pulse compression during high-speed target detection.
For example, when the transmission frequency is 10 GHz, the transmission pulse width is 1000 μs, the phase dispersion bandwidth is 1 MHz, and the target speed is 1 km / s, the distance offset is 10 km. Thus, the distance offset is a major factor of distance measurement error.

On the other hand, Patent Document 1 discloses a technique for improving distance measurement accuracy by correcting a distance offset.
Hereinafter, the technique described in Patent Document 1 will be described in detail with reference to the schematic diagram shown in FIG. 5 based on the block diagram shown in FIG. 4.

  As shown in FIG. 4, a radar pulse compression apparatus described in Patent Document 1 includes an FFT (Fast Fourier Transform) circuit 501, a multiplier 502, an IFFT (Inverse FFT) circuit 503, a signal detector 504, and a measurement. It comprises a distance 505, a non-linear FM (Frequency Modulation) reference signal generator 507, a maximum value detector 508, a selector circuit 509, and an approach speed calculator 510.

  The FFT circuit 501 receives a digital received signal obtained by digitizing a radar received signal, converts it into a frequency domain, divides it into a plurality of channels, and outputs the divided signal. Multiplier 502 multiplies the received signal converted into the frequency domain by the reference signal from nonlinear FM reference signal generator 507. The IFFT circuit 503 converts the multiplied signal into a time domain signal. The signal detector 504 detects a target signal by performing threshold determination on the input signal. The distance measuring device 505 measures the distance from the difference between the transmission time of the transmission pulse and the detection time of the detected target signal.

  The non-linear FM reference signal generator 507 generates a plurality of non-linear chirp modulation reference signals modulated at a Doppler frequency at regular intervals. The maximum value detector 508 detects a signal having the maximum amplitude among the signals from the signal detector of each channel, and outputs the channel number to the selector circuit 509 and the approach speed calculator 510. The selector circuit 509 outputs a signal of the selected channel. The approach speed calculator 510 calculates a target speed from the Doppler frequency of the selected channel.

The method described in Patent Document 1 is a technique that uses the characteristics of a non-linear chirp pulse, which is one of the modulation methods of a transmission pulse. Non-linear chirp modulation transmission pulses are more sensitive to Doppler frequency modulation than linear chirp modulation transmission pulses. If the Doppler frequency differs between the reference signal and the received pulse, the pulse compression gain will drop and the compressed The amplitude value becomes smaller. Conversely, the linear chirp pulse has a large distance offset, but the decrease in pulse compression gain is small compared to the non-linear chirp modulation.
For this reason, multiple reference signals modulated at the Doppler frequency corresponding to the assumed target speed are generated, pulse compression is processed in parallel on multiple channels, and the output of the channel with the maximum amplitude value is selected. Thus, the target speed can be estimated. The target distance can be calculated by calculating and correcting the distance offset based on the Doppler frequency after calculating the target speed using the technique of Patent Document 1.

  In Patent Document 2, the transmission / reception unit of the ultrasonic diagnostic apparatus performs transmission and reception of waves at unequal intervals in the first operation direction of the subject. Then, the mixer and LPF perform quadrature detection on the obtained received signal to generate an IQ signal, and the least square filter extracts a Doppler signal component from the IQ signal by a least squares fitting of a polynomial. . Then, the autocorrelator performs autocorrelation processing between adjacent Doppler signals obtained at short transmission / reception intervals, and the computing unit calculates a flow velocity value, a power value, and a dispersion value based on the autocorrelation result. . The transmission / reception unit reduces the frame frequency by performing unequal interval transmission / reception in the second scanning direction at a long transmission / reception interval in the transmission / reception wave in the first scanning direction set at unequal intervals. There is disclosed an ultrasonic diagnostic apparatus that generates color Doppler image data excellent in low flow velocity detection capability and high flow velocity detection capability.

  Further, in Patent Document 3, the pseudo distance change calculation unit integrates Doppler components of carriers used for signal transmission from GPS satellites from a predetermined time point, and calculates a pseudo distance change amount. The offset estimation unit obtains a difference between the pseudo distance obtained by phase synchronization of the PN code and the pseudo distance change obtained by integrating Doppler components, and smoothes the difference to remove high-frequency fluctuations in the code pseudo distance. The carrier pseudo distance calculation unit calculates the pseudo distance based on the difference (offset estimation value) from which the high-frequency fluctuation is removed and the pseudo distance change amount. The positioning calculation unit performs the positioning calculation based on the pseudo distance calculated by the carrier pseudo distance calculation unit, the pseudo distance calculated by the satellite position calculation unit, and the satellite position calculated by the satellite position calculation unit, thereby calculating the pseudo distance. A GPSS receiver and its positioning method are disclosed in which the accuracy is determined and the positioning accuracy is improved.

  Further, in Patent Document 4, a moving target that includes a reference signal generating unit, a pulse compressing unit, and a pulse Doppler processing unit, performs integration processing corresponding to the moving target, and outputs a range bin / Doppler bin two-dimensional signal signal. Corresponding coherent accumulating means and movement that specifies and outputs a movement target value by accumulating signals that exceed the set threshold value of a three-dimensional signal of range bin, Doppler bin, and time by repeating this processing in time-series input signals A radar apparatus is disclosed which has a high integration time limit even if a target having non-coherent integration means corresponding to a target is measured with respect to a high-speed moving target even if a reception having a bandwidth depending on its acceleration or size is measured.

JP 05-107349 A JP 2005-176997 A JP 07-198821 A Japanese Patent Laid-Open No. 08-179037

The first problem of each of the conventional techniques described above is that the higher the target speed, the more the number of channels to be subjected to pulse compression needs to be increased, and the processing load increases. The H / W (hardware) scale of the system will greatly increase.
The reason is that the number of channels for pulse compression is required for each Doppler frequency at regular intervals within the range of the maximum target speed assumed from speed 0.

The second problem of each prior art is that a quantization error occurs in distance accuracy.
This is because the measured value of the target speed is obtained as a discrete value of the speed corresponding to the Doppler frequency of the reference signal of each channel, and the measured value of the distance is also a discrete value corresponding to the discrete value of the target speed. .

  The present invention has been made in view of such circumstances, and a pulse compression apparatus that does not significantly increase the H / W scale of a processing apparatus and that does not cause quantization errors in distance accuracy. It is intended to provide.

  In order to solve the above-described problems, the present invention relates to a pulse compression apparatus, which distributes a digital received signal obtained by digitizing a radar received signal to a plurality of channels, and has a maximum gaze direction speed of a detection target as an upper limit in advance. A reference signal generator for generating a reference signal corresponding to each Doppler frequency of the determined line-of-sight speed for each channel, and a second pulse for performing a pulse compression process on the distributed digital reception signal using the reference signal The target is the same when the distance offset is corrected in each channel, the target detector that detects the target signal by threshold judgment from the signal after pulse compression output from the second pulse compressor Correlation data extractor that extracts target signal data estimated as, and multiple extracted target signal data on the horizontal axis Peak detector that obtains the Doppler frequency corresponding to the peak value of the approximate curve of the graph obtained by performing curve fitting of each plot point on the graph when taking the frequency and taking the amplitude value of each channel on the vertical axis And a correction value calculator for determining a distance correction value by calculating a distance offset by pulse compression from the target speed obtained by obtaining a target speed corresponding to the obtained Doppler frequency.

According to the present invention, the distance measurement accuracy can be improved by correcting the distance offset generated by the pulse compression for the high-speed target without increasing the H / W scale of the processing device that performs the pulse compression.
The reason is that even if the Doppler frequency of the reference signal deviates from the received pulse to some extent, the same target is pulse-compressed to a different distance by using a linear chirp pulse that can detect the amplitude value with a small drop in gain of pulse compression. As shown in Fig. 1, the amplitude values of all the channels that can be assumed are extracted, and the curve is plotted for each plot on the graph when the horizontal axis is the Doppler frequency and the vertical axis is the amplitude value of each channel. This is because fitting is performed to obtain the Doppler frequency corresponding to the peak value of the approximate curve of the graph.

In this case, the number of channels for pulse compression need only be the number of channels necessary for curve fitting, and it is not necessary to arrange the channels without gaps to cover the required speed range as in the prior art, so the number of channels is small. It is possible to
In addition, since the peak value of the approximate curve is detected, the Doppler frequency can be measured without causing a quantization error.
In this way, since the Doppler frequency can be measured with a small number of channels without generating a quantization error, the distance offset generated by pulse compression at a high-speed target can be reduced without significantly increasing the H / W scale of the processing apparatus. By correcting, the effect of improving the distance accuracy can be obtained.

It is a figure for demonstrating the effect of this invention. It is a block diagram which shows embodiment of this invention. It is a block diagram which shows other embodiment of this invention. 10 is a block diagram showing a configuration of a radar pulse compression device described in Patent Document 1. FIG. 6 is a schematic diagram for explaining a distance offset in a radar pulse compression device described in Patent Document 1. FIG.

  Hereinafter, a radar pulse compression apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

Embodiment

  FIG. 2 is a diagram showing a first embodiment of a radar pulse compression apparatus according to the present invention, in which a distributor 101, a pulse compressor A102, a pulse compressor B103, and a reference signal generator 104 are shown. A block configuration including a target detector 105, a correlation data extraction circuit 106, a peak detector 107, a correction value calculator 108, and a distance corrector 109 is shown.

  The distributor 101 distributes a digitized radar reception signal input from the outside to a plurality of channels. The pulse compressor A102 performs pulse compression on the radar reception signal by using a reference signal that is not modulated with the Doppler frequency, that is, the line-of-sight velocity is zero. The pulse compressor B103 performs pulse compression using the reference signal input from the reference signal generator 104. The reference signal generator 104 generates a reference signal corresponding to a plurality of predetermined gaze direction speed Doppler frequencies for each channel with the maximum gaze direction speed of the detection target as an upper limit. The target detector 105 detects a target signal by threshold determination from the pulse-compressed signal output from the pulse compressor A102 or the pulse compressor B103.

  The correlation data extractor 106 extracts target signal data that is estimated to be the same target when the distance offset is corrected in each channel. The peak detector 107 performs curve fitting of each plot on the graph when the horizontal axis represents the Doppler frequency and the vertical axis represents the amplitude value of each channel of the plurality of extracted target data. A Doppler frequency corresponding to the peak value of the approximate curve is obtained. The correction value calculator 108 calculates a gaze direction velocity corresponding to the obtained Doppler frequency, calculates a distance offset by pulse compression from the obtained gaze direction velocity, and outputs a correction value. The distance corrector 109 calculates the target distance by adding the correction value calculated by the correction value calculator 108 to the distance obtained by the channel of the pulse compressor A102.

  FIG. 3 is a diagram showing a second embodiment of a radar pulse compression apparatus according to the present invention, in which a distributor 101, a pulse compressor A102, a pulse compressor B103, a reference signal generator / generator 104, and a target detector are shown. The operations of 105, the peak detector 107, the correction value calculator 108, and the distance corrector 109 are the same as those of the first embodiment shown in FIG.

  In the second embodiment, only when the target is detected by the target detector 105 after being pulse-compressed by the pulse compressor A102 with the reference signal corresponding to the line-of-sight velocity 0, the detected target distance is the center. The region extractor 104A extracts a received signal in a region expanded in a predetermined range stored in the memory 110, inputs the signal to the distributor 101, performs pulse compression processing in the pulse compressor B103, and then detects the amplitude. The amplitude value is detected by the device 111 and the subsequent processing by the peak detector 107 and the correction value calculator 108 is performed based on the detected amplitude value.

  By doing in this way, unless the target is detected, it is not necessary to perform the pulse compression in parallel with a plurality of channels. Compared to the case of the first embodiment in which the parallel processing of the pulse compressor B103 is always performed. The processing load can be reduced, and when the target is detected, the distance offset can be corrected.

  The pulse compression apparatus of the present invention can be used in various radar apparatuses that transmit linear chirp pulses, with functions and apparatus forms other than those described in the embodiments, usage methods, and the like being arbitrary.

101 Distributor 102 Pulse compressor A
103 Pulse compressor B
104 Reference signal generator 104A Region extractor 105 Target detector 106 Correlation data extractor 107 Peak detector 108 Correction value calculator 109 Distance corrector 110 Memory 111 Amplitude detector

Claims (5)

A distributor for distributing a digital reception signal obtained by digitizing a radar reception signal to a plurality of channels;
A reference signal generator that generates a reference signal corresponding to each Doppler frequency of a predetermined gaze direction speed, with the maximum gaze direction speed of the target to be detected as an upper limit;
A second pulse compressor for performing a pulse compression process on the distributed digital reception signal using the reference signal;
A target detector for detecting a target signal by threshold determination from a signal after pulse compression output from the second pulse compressor;
A correlation data extractor that extracts target signal data that is estimated to be the same target when the distance offset is corrected in each channel;
Approximation of the graph obtained by performing curve fitting of each plot point on the graph when the horizontal axis represents the Doppler frequency and the vertical axis represents the amplitude value of each channel. A peak detector for determining the Doppler frequency corresponding to the peak value of the curve;
A correction value calculator for obtaining a target speed corresponding to the obtained Doppler frequency, calculating a distance offset by pulse compression from the obtained target speed, and obtaining a distance correction value;
A pulse compression apparatus comprising: The pulse compression device according to claim 1, wherein
A first pulse compressor that performs pulse compression processing with a reference signal corresponding to a line-of-sight velocity of 0;
A pulse compression apparatus comprising: a distance corrector that obtains a true distance by adding the distance correction value to the measured distance obtained by the first pulse compressor.   The pulse compression apparatus according to claim 1 or 2, wherein a chirp pulse system that performs frequency modulation within a transmission pulse and transmits is used as a transmission pulse modulation system in the pulse compression.   The chirp pulse is characterized in that the modulation frequency in the transmission pulse changes linearly, and the frequency modulation in the reception pulse changes from the transmission pulse by the Doppler frequency corresponding to the target line-of-sight velocity. The pulse compression apparatus as described in any one of thru | or 3.   5. The pulse compression device according to claim 1, wherein a peak amplitude position of the linear chirp pulse after pulse compression is offset in accordance with a line-of-sight direction velocity.

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