JP2016024173A - Radar system and radar signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a false image derived from an autonomous response signal in a radar system utilizing pulse compression.SOLUTION: A first modulated pulse wave and a second modulated pulse wave different from the first modulated pulse wave are alternately designated as a modulated pulse wave in relation to each sweep. A non-modulated pulse wave and the modulated pulse wave are transmitted, and a receiving signal is received during each sweep. A first separation signal having a frequency band corresponding to that of the modulated pulse wave is separated from the receiving signal received during each sweep. Each of the first separation signals obtained during respective sweeps is subjected to compression processing of correlating the first separation signal with the modulated pulse wave designated by a transmission unit. Thus, a first compressed signal based on the first modulated pulse wave and a second compressed signal based on the second modulated pulse wave are produced, and a correlation signal is produced by correlating the first compressed signal with the second compressed signal.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a radar apparatus and a radar signal processing method using pulse compression.

  In a conventional radar apparatus, in particular, in a situation where the transmission power cannot be increased due to hardware limitations, the pulse compression method is used as a technique for improving the transmission power in a pseudo manner and improving the long-range detection performance. It is known to use. A typical method as the pulse compression method is to transmit a linear FM modulated wave (linear chirp wave), receive a reflected wave reflected from a reflection source such as a target, and the like. This is a method of obtaining a pulse compression wave by taking the above correlation.

  By the way, in the signal received by the radar device, in addition to the reflected wave reflected by the reflection source such as the target, a response wave from the automatic response device that receives the radar signal and automatically responds may be mixed. Examples of such an automatic response device include a SART (Search And Rescue Transponder) and a radar beacon (hereinafter referred to as a racon). In some cases, it is required to display an automatic response signal from these automatic response devices with a radar device.

  Here, SART and racon will be described. FIG. 7 is an explanatory diagram showing the relationship between transmission and reception between a conventional radar device and SART. FIG. 8 is an explanatory diagram showing a transmission / reception relationship between a conventional radar apparatus and a racon.

  SART is used for finding and locating surviving boats (lifeboats and liferafts). When a radar signal of a specific frequency is received, a signal is returned in response thereto. As shown in FIG. 7A, when a radar signal from a general radar device 50 is received by the SART 60, the SART 60 generates a frequency-modulated wave a plurality of times as shown in FIGS. 7B and 7C. Reply repeatedly. In the radar device 50, as shown in FIG. 7 (d), in order to pass only the components of the reception band of the receiver, the display device of the radar device 50 has a plurality of rearward components from the position where the SART 60 exists. The volatile point is displayed.

  A racon is installed in a radio beacon station and returns a signal in response to a radar signal having a specific frequency, similar to a SART. Specifically, as shown in FIG. 8 (a), when the radar signal from the radar apparatus 50 is received by the racon 70, the racon 70 receives the encoded response signal as shown in FIG. 8 (b). Reply. As shown in FIG. 8C, the radar apparatus 50 passes only the components in the reception band of the receiver in response to this response signal. Therefore, the display device of the radar apparatus 50 has a racon. A volatile point is displayed behind the position.

  The racon includes a frequency agile racon that responds at the same frequency as the carrier frequency of the received radar signal, and a low-speed sweep racon that responds at a preset carrier frequency based on the response setting value stored in the racon. is there.

  When a radar apparatus using pulse compression receives an automatic response signal as described above, a false image is generated by expanding the automatic response signal in the distance direction as shown in FIG. As a result, the automatic response signal cannot be correctly displayed.

  Further, a technique for removing interference by a jitter method (for example, Patent Document 1) is known for a radar apparatus.

U.S. Pat. No. 4,973,968

  However, according to the method of removing interference by the above-described jitter method, the pulse expanded in the distance direction cannot be sufficiently removed, and as a result, generation of a false image due to an automatic response signal cannot be prevented. There was a problem.

  Embodiments of the present invention have been made to solve the above-described problems, and an object thereof is to prevent generation of a false image due to an automatic response signal.

  In order to solve the above-described problem, the radar apparatus according to the present embodiment is a radar apparatus including an antenna that transmits a pulse wave for each sweep and receives a reflected wave from a reflection source and an automatic response signal from an automatic response apparatus. Then, the first modulated pulse wave and the second modulated pulse wave different from the first modulated pulse wave are alternately set as the modulated pulse wave for each sweep, and the unmodulated pulse wave, the unmodulated pulse wave and the frequency are set. A transmitting unit that transmits the modulated pulse wave having a different band by the antenna, a receiving unit that receives a received signal corresponding to each sweep, and a frequency band corresponding to the modulated pulse wave from the received signal of each sweep A compression process is performed by correlating the separation unit that separates the first separation signal and the first separated reception signal of each sweep with the modulated pulse wave set by the transmission unit. A compression unit for generating a first compressed signal based on the first modulated pulse wave and a second compressed signal based on the second modulated pulse wave; and correlating the first compressed signal and the second compressed signal. And a correlation unit for generating a correlation signal.

  According to the embodiment of the present invention, generation of a false image due to an automatic response signal can be prevented.

It is the schematic which shows the hardware constitutions of the radar apparatus which concerns on embodiment of this invention. It is a block diagram which shows the function structure of a signal processing part. It is a flowchart which shows operation | movement of a signal processing part. It is a wave form diagram showing the process by a signal processing part. It is a wave form diagram showing a modulation pulse wave. It is a wave form diagram showing the waveform of a pulse-compressed automatic response signal. It is explanatory drawing showing the relationship of transmission / reception with the conventional radar apparatus and SART. It is explanatory drawing showing the relationship of transmission / reception with the conventional radar apparatus and racon.

1
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the hardware configuration of the radar apparatus according to the embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating a hardware configuration of a radar apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, a radar device 10 includes an antenna 12 that transmits and receives radio waves while rotating, a transceiver unit 14 that includes a semiconductor amplifier and a circulator that switches between transmission and reception, and that performs amplification and transmission / reception switching. / A converter 16, A / D converter 18, and signal processing unit 30. The radar apparatus 10 is connected to an indicator (not shown) provided with a display device that displays a radar image.

  The D / A converter 16 converts the digital transmission signal output from the signal processing unit 30 into an analog transmission signal and outputs the analog transmission signal to the transceiver unit 14, and the A / D converter 18 is output from the transceiver unit 14. The analog reception signal is converted into a digital reception signal and output to the signal processing unit 30. The signal processing unit 30 includes a CPU (Central Processing Unit) 31 and a memory 32, and the CPU 31 and the memory 32 cooperate to execute various functions described later.

  Next, the functional configuration of the signal processing unit will be described. FIG. 2 is a block diagram illustrating a functional configuration of the signal processing unit.

  As shown in FIG. 2, the signal processing unit 30 includes a transmission data storage unit 320 that stores first modulated pulse wave data and second modulated pulse wave data as two different types of modulated pulse transmission waveform data, and a received signal. And a reception data storage unit 321 that stores a signal being processed for each sweep, a transmission wave generation unit 310 that generates an unmodulated pulse transmission signal and a modulated pulse transmission signal, a reception unit 311 that receives a reception signal, and a reception signal Is separated into a first separated signal and a second separated signal, a compression unit 313 that performs compression processing on the first separated signal, and an interference signal from the compressed signal obtained by compressing the first separated signal. A correlation unit 314 that generates a correlation signal from which the automatic response signal is removed, a synthesis unit 315 that generates a combined signal by combining the correlation signal and the second separated signal, and a radar image of the combined signal And an output unit 316 for outputting to the indicator, as a function as No..

  Next, the operation of the signal processing unit will be described. FIG. 3 is a flowchart showing the operation of the signal processing unit. FIG. 4 is a waveform diagram showing processing by the signal processing unit. FIG. 5 is a waveform diagram showing a modulated pulse wave. FIG. 6 is a waveform diagram showing the waveform of the pulse-compressed automatic response signal.

  As shown in FIG. 3, first, the transmission wave generation unit 310 reads the first modulated pulse wave data from the transmission data storage unit 320 (step S101). Here, the first modulated pulse wave is specifically an up-chirp wave whose frequency increases as time passes, as shown in FIG. The transmission wave generation unit 310 sets the modulation pulse wave in the transmission signal to the first modulation pulse wave based on the read first modulation pulse wave data, and generates a transmission signal transmitted by the antenna 12 (step S102). .

  Here, the transmission signal will be described. As shown in FIG. 4A, the transmission signal includes an unmodulated pulse wave S1, which is a short pulse wave with a short pulse width, and a modulated pulse having a longer pulse width than the unmodulated pulse wave S1, as shown in FIG. Wave S2 is included. Here, the modulation pulse wave may be either a linear chirp wave whose frequency changes linearly or a non-linear chirp wave whose frequency changes nonlinearly. The non-modulated pulse wave and the modulated pulse wave are set so that their frequency bands do not overlap. Further, an unmodulated pulse wave with a short pulse width is searched for a short distance from the antenna 12 and a search for a SART / Racon signal for synthesis. A modulated pulse wave with a long pulse width is a long distance from the antenna 12. In order to perform a long distance search, the time interval between the unmodulated pulse wave and the modulated pulse wave (hereinafter referred to as the first time T1) is a distance range (display distance range) required to be displayed on the indicator. ). One sweep means a sweep operation of one cycle based on the transmission repetition cycle (second time T2) of the antenna 12. The second time T2 is set to be twice or more the first time T1.

  When transmission / reception is performed from the antenna 12 via the transceiver unit 14 based on the transmission signal generated by the transmission wave generation unit 310, a reception signal as illustrated in FIG. 4B is received by the reception unit 311 and received. It is stored in the data storage unit 321 (step S103). Since the transmission wave is strong, it is received as R1 and R2 by the receiving unit 311 as a non-modulated pulse wave and a modulated pulse wave due to wraparound in the transceiver unit 14, respectively.

  Here, the relationship between the target and the automatic response device in the sweep range and the received signal will be described. When the target exists at a short distance, the unmodulated pulse wave is reflected by the short distance target, and the reflected wave is received by the antenna 12 at a time corresponding to the propagation time. On the other hand, the modulated pulse wave has a long transmission pulse width, and thus is reflected during transmission and returns to the antenna 12. During transmission, the receiver is saturated due to the sneak of the transmission wave, and the reflected wave from the target received during this period is not correctly displayed.

  In addition, when the target exists at a long distance, both the unmodulated pulse wave and the modulated pulse wave are reflected on the long-distance target, so that the reflected wave of the unmodulated pulse wave and the reflected wave of the modulated pulse wave are respectively As shown as R3 and R4 in FIG. 4B, the reflected wave is received by the antenna 12 at a time corresponding to the propagation time. These reflected waves basically have the same frequency characteristics as the transmission pulse wave.

  On the other hand, when the automatic response device exists in the sweep range, the automatic response device responds to the non-modulated pulse wave S1, and is determined according to the automatic response device as shown as R5 in FIG. 4B. An automatic response signal having frequency characteristics is received by the antenna 12. Similarly, when the automatic response device responds to the modulation pulse S2, an automatic response signal is received by the antenna 12, as indicated by R6 in FIG.

  Next, as illustrated in FIG. 4C, the separation unit 312 receives the short-pulse and the first separation signal corresponding to the modulated pulse wave S <b> 2 with respect to the reception signal for one sweep received by the reception unit 311. Separated into a second separated signal corresponding to the wave S1 (step S104). Specifically, the separation unit 312 separates the first separated signal having the frequency band of the modulated pulse wave S2 and the second separated signal having the frequency band of the short pulse wave S1 by frequency filtering. Here, the first separated signal includes an automatic response having R2 which is a wraparound of the modulated pulse wave as a transmission wave, R4 which is a reflected wave from the target with respect to the modulated pulse wave, and a frequency band which at least partially overlaps the modulated pulse wave. The signal R60 is included. The second separation signal includes R1 that is a wraparound of a short pulse wave as a transmission wave, R3 that is a reflected wave from the target with respect to the short pulse wave, and an automatic response signal having a frequency band that at least partially overlaps the short pulse wave R50 is included.

  Next, the compression unit 313 performs pulse compression on the first separated signal (step S105). This pulse compression is performed by taking a correlation with the first separated signal using the waveform set in the modulated pulse wave stored in the transmission data storage unit 320 as a reference signal.

  After pulse compression by the compression unit 313, the correlation unit 314 determines whether there are a plurality of compressed signals (step S106).

  When there are not a plurality of compressed signals (NO in step S106), the transmission wave generating unit 310 waits until the next sweep, and determines whether the second modulated pulse wave is set as the modulated pulse wave (step S107). .

  When the second modulation pulse wave is not set as the modulation pulse wave (step S107, NO), the transmission wave generation unit 310 reads the second modulation pulse wave data from the transmission data storage unit 320 (step S108). Here, the second modulated pulse wave is, specifically, a down chirp wave whose frequency decreases as time passes, as shown in FIG. 5B. In this down chirp wave and up chirp, the upper and lower limits of the instantaneous frequency change range are the same. The transmission wave generation unit 310 sets the modulation pulse wave in the transmission signal to the second modulation pulse wave based on the read second modulation pulse wave data, and generates a transmission signal transmitted by the antenna 12 (step S102). Thereafter, the processes of steps S103 to S106 are performed.

  On the other hand, when the second modulated pulse wave is set as the modulated pulse wave in the determination in step S107 (step S107, YES), the transmission wave generating unit 310 receives the first modulated pulse wave data from the transmission data storage unit 320. Read (step S101).

  Further, when it is determined in step S106 that there are a plurality of compressed signals (step S106, YES), the correlation unit 314 removes the automatic response signal included in the first separated signal (step S109).

  Here, a method for removing the automatic response signal will be described. At the time of step S109, the received data storage unit 321 stores the first compressed signal and the second compressed signal as signals being processed as compressed signals in the current sweep and the previous sweep. Here, the first compressed signal has a correlation between the first separated signal obtained by separating the received signal in the sweep in which the first modulated pulse wave is set as the modulated pulse wave, and the first modulated pulse wave as the reference signal. Thus, pulse compression is performed. Further, the second compressed signal is obtained by correlating the first separated signal obtained by separating the received signal in the sweep in which the second modulated pulse wave is set as the modulated pulse wave and the second modulated pulse wave as the reference signal. Pulse compression was performed.

  The first compressed signal and the second compressed signal correspond to the wraparound of the modulated pulse wave, respectively, and R20a and R20b that are not properly compressed because the signal is saturated, and the reflected wave from the target with respect to the modulated pulse wave Compressed R40a and R40b are included. Further, as shown in FIG. 6A, the first compressed signal includes R60a in which a plurality of pulses as the automatic response signal R60 are stretched in the time direction in an up-chirp manner, and the second compressed signal As shown in FIG. 6B, the signal includes R60b obtained by extending a plurality of pulses as the automatic response signal R60 in the time direction in a down-chirp manner.

  The correlation unit 314 generates a signal obtained by correlating the first compressed signal and the second compressed signal as described above as a correlation signal as shown in FIG. Remove the response signal. Here, the correlation unit 314 may obtain a correlation between the first compressed signal and the second compressed signal based on the instantaneous frequency, and also divides the first compressed signal and the second compressed signal into a plurality of units at a predetermined time interval. Correlation may be taken for each. Here, the first compressed signal and the second compressed signal are correlated in a state where the transmission time points of the modulated pulse waves are matched.

  After the correlation signal is generated, the combining unit 315 combines the correlation signal and the second separated signal to generate a combined signal (Step S110). In this synthesis, since the second separated signal is acquired for two sweeps, the second separated signal having a high average reception intensity between sweeps is used. Further, the synthesis unit 315 matches the transmission time point of the short pulse wave in the adopted second separated signal with the transmission time point of the modulated pulse wave in the correlation signal, compares the reception intensity at each time point during one sweep, The higher one is adopted, and the second separated signal is adopted between the transmission time and the end time of R21 to generate a composite signal. According to such a synthesized signal, as shown in FIG. 4 (f), R1 in the second separated signal, R41 in the correlation signal, and R50 in the second separated signal are respectively Y1, Y2, and Y3 in the synthesized signal. Become.

  After the synthesized signal is generated, the output unit 316 outputs a radar video signal to the indicator based on the synthesized signal (step S110), and the transmission wave generating unit 310 again receives the first modulation from the transmission data storage unit 320. The pulse wave data is read (step S101).

  As described above, a different modulation pulse wave is set for each adjacent sweep, and the compression process is performed by correlating the first separated signal and the set modulation pulse wave for each sweep, and the two sweeps in the adjacent sweep are performed. By correlating the two compressed signals with only the automatic response signals between the compressed signals being significantly different in waveform, the automatic response signal causing the false image can be removed. Further, according to such a removal method, since a signal having low correlation with the transmitted modulated pulse wave is removed, it is determined whether the automatic response signal is a SART or a racon. Can be removed without any problems. The first modulated pulse wave and the second modulated pulse wave are chirp waves whose instantaneous frequencies are different from each other in a state where the start points thereof coincide with each other and both are within a predetermined frequency band. desirable.

  The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Radar apparatus 12 Antenna 310 Transmission wave generation part 311 Reception part 312 Separation part 313 Compression part 314 Correlation part 315 Synthesis | combination part

Claims (6)

A radar device including an antenna that transmits a pulse wave for each sweep and receives a reflected wave from a reflection source and an automatic response signal from an automatic response device,
A first modulated pulse wave and a second modulated pulse wave different from the first modulated pulse wave are alternately set as a modulated pulse wave for each sweep, and the unmodulated pulse wave, the unmodulated pulse wave, and the frequency band are A transmitter for transmitting the different modulated pulse waves by the antenna;
A receiving unit for receiving a received signal corresponding to each sweep;
A separation unit that separates a first separated signal having a frequency band corresponding to the modulated pulse wave from the received signal of each sweep;
For each first separated signal of each sweep, a compression process is performed by correlating with the modulated pulse wave set by the transmitter, and the first compressed signal and the second modulated pulse wave based on the first modulated pulse wave A compression unit for generating a second compressed signal based on
A radar apparatus comprising: a correlation unit that generates a correlation signal by correlating the first compressed signal and the second compressed signal.   The radar apparatus according to claim 1, wherein the first modulated pulse wave is an up-chirp wave, and the second modulated pulse wave is a down-chirp wave. The separation unit separates the received signal of each sweep into the first separated signal and a second separated signal having a frequency band corresponding to the unmodulated pulse wave,
The radar apparatus according to claim 1, further comprising a combining unit that combines the second separated signal and the correlation signal to generate a combined signal. A radar signal processing method for transmitting a pulse wave for each sweep and receiving a reflected wave from a reflection source and an automatic response signal from an automatic response device,
A first modulated pulse wave and a second modulated pulse wave different from the first modulated pulse wave are alternately set as a modulated pulse wave for each sweep, and the unmodulated pulse wave, the unmodulated pulse wave, and the frequency band are Sending different modulated pulse waves,
Receive the received signal corresponding to each sweep,
Separating a first separated signal having a frequency band corresponding to the modulated pulse wave from the received signal of each sweep;
For each first separated signal of each sweep, a compression process is performed by correlating with the modulated pulse wave set by the transmitter, and the first compressed signal and the second modulated pulse wave based on the first modulated pulse wave And a second compressed signal based on
A radar signal processing method for causing a computer to execute a process of generating a correlation signal by correlating the first compressed signal and the second compressed signal.   The radar signal processing method according to claim 4, wherein the first modulated pulse wave is an up-chirp wave, and the second modulated pulse wave is a down-chirp wave. The received signal of each sweep is separated into the first separated signal and the second separated signal having a frequency band corresponding to the unmodulated pulse wave,
6. The radar signal processing method according to claim 4 or 5, further causing the computer to execute a process of generating a combined signal by combining the second separated signal and the correlation signal.

Images