JP2008151698A - Radar equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To save timely resource by needing no transmission and receiving of short transmission pulses for covering a blind region. <P>SOLUTION: Radar equipment periodically, which transmits the transmission pulses modulating a frequency, pulse-compresses to receive reflection pulses reflected from targets and detects the positions of the targets together with the pulse compression result, includes: pulse compressors 4a-4e for a plurality of blind regions performing pulse compression processing by preparing reference function having band width of frequency modulation corresponding to different receiving pulse width by each and using the different reference function; and a plurality of target detectors 6a-6e for performing target detection processing by using the pulse compression processing result by the plurality of the pulse compressors 4a-4e. The radar equipment detects the targets in the blind region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radar apparatus that irradiates a target with radio waves and detects the position of the target based on radio waves reflected from the target.

  In order to satisfy the distance performance and distance resolution at the same time, the conventional radar device transmits a long pulse signal, performs pulse compression processing on the received signal, and performs target detection processing on the signal after pulse compression. By doing so, the presence / absence of the target is determined and the target distance is measured. That is, in a conventional radar using pulse compression, when detecting a target at a long distance, a long pulse having a transmission time of several tens of the pulse repetition period is used in order to improve the average transmission power. When a long pulse is used, since it cannot be received during transmission, a large blind region in which a target cannot be detected occurs in a short distance. For example, if the duty (transmission pulse width / pulse repetition period) is set to 30%, 30% on the short distance side of the covered area (instrument range) becomes a blind area.

  In order to cover such a blind region, in Patent Document 1, a transmission signal obtained by adding a chirp signal having a short pulse and a different chirp frequency after a long pulse is used, and a radar reflected wave by this transmission signal is received, The received reflected wave is Fourier-transformed and divided into two frequency band spectrums, and each pulse is obtained by inverse Fourier-transforming the vector product of the two spectrums and the individual filter coefficients created from the long and short chirp signals. The reflected wave corresponding to the launch time position is obtained.

JP 2004-53569 A

  However, in the method of Patent Document 1 for separately transmitting such a short transmission pulse, a time resource is used for transmission / reception of a short transmission pulse for covering the blind region, and the repetition cycle of the transmission pulse becomes long. There's a problem.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a radar apparatus that can save time resources by making it unnecessary to transmit and receive a short transmission pulse for covering a blind area. Objective.

  In order to solve the above-described problems and achieve the object, the present invention periodically transmits a frequency-modulated transmission pulse, receives a reflected pulse reflected from a target, and performs pulse compression. A reference function having a frequency modulation bandwidth corresponding to a different received pulse width is prepared, and the pulse compression processing is performed using the different reference function. A plurality of blind region pulse compressors, and a plurality of target detectors that perform target detection processing using the result of pulse compression processing by the plurality of pulse compressors, and only receive pulses having a width shorter than the transmission pulse. It is characterized by detecting a target in a blind area where it cannot be received.

  According to the present invention, pulse compression is performed using a reference function having frequency modulation bandwidths corresponding to different received pulse widths, and target detection processing in the blind region is performed using these pulse compression processing results. As a result, transmission / reception of a short transmission pulse for covering the blind area becomes unnecessary, and there is an effect that time resources can be saved. Further, since the received pulse and the reference function have the same modulation band, normal pulse compression can be performed, and an increase in range side lobe that occurs when pulse compression with a different modulation band is performed does not occur.

  Hereinafter, embodiments of a radar apparatus according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a configuration diagram of a first embodiment of a radar apparatus according to the present invention. As shown in FIG. 1, the radar apparatus includes an antenna 1, a transceiver 2, a normal pulse compressor 3, a plurality of (5 in this case) Eclipse pulse compressors 4 a to 4 e, and a normal target detector 5. And a plurality of (in this case, five) low-resolution target detectors 6 a to 6 e and a distance synthesizer 7. This radar apparatus is installed on a ship or the seaside, for example.

  Next, the operation of the radar apparatus of FIG. 1 will be described. The transceiver 2 generates a transmission signal subjected to linear FM modulation (up-chirp modulation or down-chirp modulation) and outputs the transmission signal to the antenna 1. The antenna 1 radiates a transmission signal in the air and receives a reflected signal from a target. A signal received by the antenna 1 is output to the transceiver 2, amplified and frequency-converted by the transceiver 2, and output to the normal pulse compressor 3 and the plurality of Eclipse pulse compressors 4 a to 4 e.

  The operation of the normal pulse compressor 3 will be described. As shown in FIG. 2, the normal pulse compressor 3 performs a pulse compression process on a signal in a distance range excluding the blind area BL on the short distance side, that is, a signal in a distance range in which the pulse compression process can be normally performed. Here, since the reflected signal cannot be received during the transmission period of the transmission pulse, a reception pulse defect (Eclipse) as shown in FIG. 4 occurs. The blind region BL refers to a distance range in which a pulse having the same length as the transmission pulse width cannot be received, in other words, a distance range in which only a reception pulse having a pulse width shorter than the transmission pulse width can be received. As shown in FIG. 2, the normal pulse compressor 3 performs linear FM pulse compression processing on the input signal in the distance range from the rear end of the transmission pulse to the front end of the next transmission pulse, so that the blind region on the short distance side A pulse-compressed signal in a distance range excluding BL (distance range from the rear end of the blind area BL to the front end of the next transmission pulse) is output to the normal target detector 5.

  The operation of the Eclipse pulse compressors 4a to 4e will be described. As shown in FIG. 3, the Eclipse pulse compressors 4a to 4e perform linear FM Eclipse pulse compression processing on the input signal in the distance range of the blind region BL, as shown in FIG. Are output to the low-resolution target detectors 6a to 6e.

  As described above, since a loss (Eclipse) of the reception pulse occurs in the blind region BL, the reception pulse from the target in the blind region BL is shorter than the pulse width of the transmission pulse. As shown in FIG. 4, the Eclipse pulse compression processing pays attention to the fact that the modulation band Δf of the linear FM modulated wave varies depending on the reception pulse width, and the modulation bandwidth Δf that can be received for each reception distance (each reception pulse width). Is calculated in advance, a plurality of different reference functions corresponding to these modulation bands are generated in advance, and pulse compression processing is performed using the generated plurality of reference functions.

  FIG. 5 shows the concept of the pulse compression processing performed by each of the Eclipse pulse compressors 4a to 4e. The hatched portion is a received pulse portion, and the portion surrounded by a broken line is Eclipse. In addition, the diagonal straight line written in the received pulse and the Eclipse portion indicates the same modulation band as in FIG. For example, the Eclipse pulse compressor 4a performs pulse compression processing using a reference function having a modulation band Δfa corresponding to a received pulse width of 0 to Δta. The Eclipse pulse compressor 4b performs pulse compression using a reference function having a modulation band Δfb corresponding to the received pulse width of 0 to Δtb, and the Eclipse pulse compressor 4c receives received pulses of 0 to Δtc. Pulse compression processing is performed using a reference function having a modulation band Δfc corresponding to the width, and the Eclipse pulse compressor 4d performs pulse compression using a reference function having a modulation band Δfd corresponding to a received pulse width of 0 to Δtd. The Eclipse pulse compressor 4e performs pulse compression processing using a reference function having a modulation band Δfe corresponding to a received pulse width of 0 to Δte. In this case, the reception pulse width is divided into five stages, but the number of divisions is arbitrary.

  In the Eclipse pulse compression processing, since the received pulse and the reference function have the same modulation band, normal pulse compression can be performed, and an increase in the range side lobe that occurs when pulse compression with a different modulation band is performed does not occur. However, if the reception pulse width is reduced, the modulation bandwidth of the reference function is reduced accordingly, so that the pulse width after pulse compression is increased and the distance resolution is degraded.

  Further, in the Eclipse pulse compression processing, since the pulse compression processing is performed on the received pulse in which the entire transmission pulse width is not received, the target signal after the pulse compression is lower in power than the normal pulse compression. . However, since the blind region BL occurs at a short distance and the span loss is small, the detection performance for the target having the same radar effective reflection area does not deteriorate.

  The normal target detector 5 performs an S / N improvement process and an unnecessary signal removal process on the input signal, then performs an amplitude detection process, and determines the presence / absence of a target for each distance by the normal target detection process. The result is output to the distance synthesizer 7.

  The normal target detection process is shown in FIG. The normal target detection process is a process generally called CFAR. The threshold level is determined by using the received power in the reference cell in the moving window, and whether or not the target cell signal is larger than the threshold level. Is determined. That is, the arithmetic units 10 and 11 calculate the sum of the received signals of the reference cells, the arithmetic unit 12 divides the total value of the received signals of the reference cells by the number of reference cells, and the arithmetic unit 13 adds the coefficient to the division result. The threshold level is calculated by multiplication, and the comparator 14 determines the presence or absence of the target by comparing the signal in the target cell with the threshold level. The guard cell that exists between the target cell and the reference cell prevents the base level of the target signal from entering the reference cell and increasing the threshold level when the target signal exists in the target cell. The cell length is equivalent to the peak pulse width after normal pulse compression.

  Each of the low resolution target detectors 6a to 6e, like the normal target detector 5, performs an S / N improvement process and an unnecessary signal removal process on the input signal, and then performs an amplitude detection process to obtain a low resolution target. The presence / absence of the target is determined for each distance by the detection output process, and the determination result is output to the distance synthesizer 7.

  The low resolution target detection processing is shown in FIG. That is, the arithmetic units 20 and 21 calculate the sum of the received signals of the reference cells, the arithmetic unit 22 divides the total value of the received signals of the reference cells by the number of reference cells, and the arithmetic unit 23 adds the coefficient to the division result. The threshold level is calculated by multiplication, and the comparator 24 compares the signal in the target cell with the threshold level to determine the presence or absence of the target. The only difference between the low resolution target detection process and the normal target detection process is the guard cell length. In the low-resolution target detection process, the guard cell length is changed for each reception distance to obtain a cell length corresponding to the pulse width after the Eclipse pulse compression. That is, the cell lengths of the guard cells in the moving window in the plurality of low resolution target detectors 6a to 6e are made different so as to become the cell length corresponding to the pulse width after pulse compression according to the received pulse width. Specifically, since the low-resolution target detector 6a is targeted for detection with the shortest received pulse width, the peak pulse width after pulse compression is the widest, so the guard cell is also lengthened accordingly and low. Since the resolution target detector 6e has the longest received pulse width as a detection target, the peak pulse width after the pulse compression becomes the narrowest, so the guard cell is also shortened accordingly.

  The distance synthesizer 7 integrates the outputs of the normal target detector 5 and the plurality of low resolution target detectors 6a to 6e, and outputs target detection results for the entire distance range including the blind region BL.

  Since this radar apparatus operates as described above, it is possible to perform pulse compression that does not deteriorate the range side lobe even for a signal in a region that has conventionally been blind. In addition, when performing target detection for signals in areas that were previously blind, the target signal is mixed into the reference cell due to the wide pulse width after compression, leading to an increase in the threshold level, and target detection performance. Can be prevented from deteriorating. As a result, even when a long pulse is transmitted, it is not necessary to transmit and receive a short transmission pulse for covering a blind area, which can save time resources.

  As described above, the radar apparatus according to the present invention periodically transmits a frequency-modulated transmission pulse, receives the reflected pulse reflected from the target, compresses the pulse, and based on the pulse compression result, This is useful for radar devices that detect the position of an object.

It is a block diagram which shows the radar apparatus by embodiment of this invention. It is a figure which shows the input / output distance range of the normal pulse compressor by embodiment of this invention. It is a figure which shows the input / output distance range of the pulse compressor for Eclipse by embodiment of this invention. It is a figure which shows the modulation band of the reference function in the pulse compression process for Eclipse by embodiment of this invention. It is a conceptual diagram which shows the pulse compression process in the pulse compression process for Eclipse by embodiment of this invention. It is a figure explaining the normal target detection process by embodiment of this invention. It is a figure explaining the target detection process for low resolution by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Transceiver 3 Normal pulse compressor 4a-4e Eclipse pulse compressor 5 Normal target detector 6a-6e Low resolution target detector 7 Distance synthesizer

Claims (2)

In a radar apparatus that periodically transmits a frequency-modulated transmission pulse, receives a reflected pulse reflected from a target, compresses the pulse, and detects the position of the target based on the pulse compression result.
A reference function having a frequency modulation bandwidth corresponding to a different received pulse width is prepared, and a plurality of blind region pulse compressors that perform the pulse compression processing using the different reference functions;
A plurality of target detectors for performing target object detection processing using a result of pulse compression processing by the plurality of pulse compressors;
And detecting a target in a blind region in which only a received pulse having a width shorter than a transmitted pulse can be received. The plurality of target detectors determine a threshold value using a signal in a reference cell in a moving window, and perform CFAR processing for determining the presence / absence of a target based on whether or not a signal of a target cell is larger than the threshold value. Is,
The cell length of the guard cell existing between the target cell and the reference cell in the moving window in the plurality of target detectors is changed to be a cell length corresponding to the pulse width after pulse compression according to the received pulse width. The radar apparatus according to claim 1.

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