Radar device and target detection method

Abstract

To improve the target detection performance.SOLUTION: A radar device includes: a transmitting unit that transmits pulsed radio waves via an antenna; a receiving unit that receives, via the antenna, reflected waves in which the transmitted radio waves is reflected by a target; and a target detection unit that performs detection processing to detect the target. The transmitting unit transmits a second radio wave after transmitting a first radio wave. The target detection unit adds a delayed signal which is a signal obtained by delaying a first received signal based on the first radio wave and a second received signal based on the second radio wave, and performs the detection processing based on an addition result.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radar device and a target detection method. [Background technology]

[0002] Radar devices that detect targets using pulsed radio waves have been developed. For example, Patent Document 1 (JP Patent Publication No. 2016-16620) discloses the following radar device. That is, the radar device alternately executes a first detection process in which a short-distance pulse signal and a long-distance pulse signal having a pulse width longer than that of the short-distance pulse signal are transmitted and received to detect the surroundings, and a second detection process in which a medium-distance pulse signal having a pulse width longer than that of the short-distance pulse signal and a long-distance pulse signal are transmitted and received to detect the surroundings. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-16620 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the radar equation, when a pulsed radio wave is transmitted, the signal-to-noise ratio of the signal reflected by the target can be improved by increasing the transmission power, antenna gain, and pulse width of the radio wave.

[0005] In general, it is difficult to receive a reflected signal during the period when a pulsed radio wave is being transmitted. Therefore, if a radio wave with a large pulse width is transmitted to improve the signal-to-noise ratio of the reflected signal, the period during which the target cannot be detected becomes longer. Therefore, a method of shortening the period during which the target cannot be detected can be considered by increasing the number of types of pulsed radio waves transmitted and using other radio waves with shorter pulse widths.

[0006] However, when the number of pulses of radio waves transmitted and received by a radar device increases, the pulse repetition frequency (PRF) decreases, so the number of pulses that hit a target decreases, which may result in a decrease in target detection performance.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a radar device and a target detection method capable of improving target detection performance. [Means for solving the problem]

[0008] (1) In order to solve the above problems, a radar device according to one aspect of the present invention includes a transmitting unit that transmits pulsed radio waves via an antenna, a receiving unit that receives, via the antenna, waves reflected by a target from the transmitted radio waves, and a target detection unit that performs a detection process to detect the target, wherein the transmitting unit transmits a second radio wave after transmitting a first radio wave, and the target detection unit adds a delayed signal, which is a delayed signal obtained by delaying a first received signal based on the first radio wave, to a second received signal based on the second radio wave, and performs the detection process based on the addition result.

[0009] In this manner, by using the result of adding the delayed first reception signal based on the first radio wave and the second reception signal based on the second radio wave to detect a target, two reception signals with the same phase can be added, so that the signal-to-noise ratio of the signal for detecting the target can be improved. Also, the transmission interval of the first radio wave and the second radio wave can be shortened, so that the correlation between the two reception signals can be increased. Therefore, the detection performance of the target can be improved.

[0010] (2) In the above (1), the delayed signal may be a signal obtained by delaying the first received signal by a difference between a transmission timing of the first radio wave and a transmission timing of the second radio wave.

[0011] With this configuration, the phases of the two received signals to be added can be more accurately matched, thereby further improving the signal-to-noise ratio of the signal for detecting a target object.

[0012] (3) In the above (1) or (2), the transmission unit may transmit the second radio wave after transmitting the first radio wave, consecutively in time with the first radio wave.

[0013] With this configuration, the correlation between the two received signals to be added can be further increased, enabling more accurate detection of targets.

[0014] (4) In any one of (1) to (3) above, the pulse width of the first radio wave and the pulse width of the second radio wave may be the same.

[0015] With this configuration, for example, compared to a configuration in which the pulse width of the second radio wave is larger than the pulse width of the first radio wave, the radar device can shorten the radio wave transmission period and the reception period of the reflected signal of the radio wave reflected by a target, thereby suppressing radio wave interference and reflected signal interference between the radar device and other radar devices present in the vicinity of the radar device.

[0016] (5) In any one of (1) to (3) above, a pulse width of the second radio wave may be smaller than a pulse width of the first radio wave.

[0017] With this configuration, for example, compared to a configuration in which the pulse width of the second radio wave is larger than that of the first radio wave, the radar device can shorten the radio wave transmission period and the reception period of the reflected signal reflected by the radio wave from a target, thereby suppressing radio wave interference and reflected signal interference between the radar device and other radar devices present around the radar device. Also, during the period in which the pulsed radio wave is being transmitted, the reflected signal reflected by the target cannot be received. As described above, when transmitting the first radio wave and the second radio wave having different pulse widths, the configuration in which the pulse width of the second radio wave is smaller than the pulse width of the first radio wave transmitted before the second radio wave can shorten the period in which the reflected signal corresponding to the first radio wave cannot be received.

[0018] (6) In the above (5), the transmission unit may transmit the radio wave whose frequency changes over time.

[0019] With this configuration, the transmission power can be reduced and the circuit configuration can be simplified, compared to a configuration in which radio waves of a constant frequency are transmitted.

[0020] (7) In the above (6), the variation width of the frequency of the first radio wave may be the same as the variation width of the frequency of the second radio wave.

[0021] With this configuration, for example, when pulse compression processing is performed to compress the pulse widths of the delay signal and the second received signal, the pulse width of the delay signal after pulse compression processing can be made the same as the pulse width of the second received signal after pulse compression processing, making it possible to easily add the delay signal and the second received signal.

[0022] (8) In the above (6) or (7), a rate of change of the frequency of the first radio wave may be different from a rate of change of the frequency of the second radio wave.

[0023] For example, in a configuration in which the pulse width of the first radio wave and the pulse width of the second radio wave are different from each other and the pulse width of each of the delayed signal and the second received signal is compressed, in order to simply add the delayed signal and the second received signal, it is necessary to make the change width of the frequency of the first radio wave and the change width of the frequency of the second radio wave the same, and to make the pulse width of the delayed signal after the pulse compression processing the same as the pulse width of the second received signal after the pulse compression processing. As described above, in a configuration in which the pulse width of the first radio wave and the pulse width of the second radio wave are different from each other, by making the rate of change of the frequency of the first radio wave different from the rate of change of the frequency of the second radio wave, it is possible to adjust the rate of change of the frequency of the first radio wave and the rate of change of the frequency of the second radio wave so that the rate of change of the frequency of the first radio wave is the same as the rate of change of the frequency of the second radio wave, and therefore it is possible to simply add the delayed signal and the second received signal.

[0024] (9) In any of (1) to (8) above, the radar device may further include a pulse compression unit that performs a pulse compression process to compress a pulse width of each of the delayed signal and the second received signal, the pulse width of the delayed signal after the pulse compression process may be the same as the pulse width of the second received signal after the pulse compression process, and the target detection unit may perform the detection process based on a result of adding the delayed signal after the pulse compression process and the second received signal after the pulse compression process.

[0025] In this way, the configuration in which the pulse widths of the delay signal and the second received signal are compressed makes it possible to increase the signal-to-noise ratio of the signal for detecting a target, which is the sum of the delay signal and the second received signal. Also, the configuration in which the pulse width of the delay signal after pulse compression processing is the same as the pulse width of the second received signal after pulse compression processing makes it possible to simply add the delay signal and the second received signal.

[0026] (10) In order to solve the above problems, a target detection method according to one aspect of the present invention is a target detection method in a radar device, which transmits pulsed radio waves via an antenna, receives waves reflected by a target from the transmitted radio waves via the antenna, performs a detection process to detect the target, transmits a second radio wave after transmitting a first radio wave, adds a delayed signal that is a delayed signal obtained by delaying a first received signal based on the first radio wave to a second received signal based on the second radio wave, and performs the detection process based on the addition result.

[0027] In this way, by using the result of adding the delayed first reception signal based on the first radio wave and the second reception signal based on the second radio wave to detect a target, two reception signals with the same phase can be added, so that the signal-to-noise ratio of the signal for detecting the target can be improved. Also, the transmission interval of the first radio wave and the second radio wave can be shortened, so that the correlation between the two reception signals can be increased. Therefore, the detection performance of the target can be improved.

[0028] (11) In the above (10), the delayed signal may be a signal obtained by delaying the first received signal by a difference between a transmission timing of the first radio wave and a transmission timing of the second radio wave.

[0029] By using this method, the phases of the two received signals to be added can be more accurately matched, thereby further improving the signal-to-noise ratio of the signal for detecting a target object.

[0030] (12) In the above (10) or (11), after transmitting the first radio wave, the second radio wave may be transmitted consecutively in time to the first radio wave.

[0031] This method can further increase the correlation between the two received signals to be added, enabling more accurate detection of targets. Effect of the Invention

[0032] According to the present invention, it is possible to improve the detection performance of a target. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a diagram showing a configuration of a radar device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a conceptual diagram illustrating an example of a transmission wave transmitted by the radar device according to the embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram conceptually illustrating an example of a reception signal received by the radar device according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram conceptually illustrating an example of a delayed signal transmitted in a radar device according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram for explaining the pulse compression process performed by the radar device according to the embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of an added signal generated by the radar device according to the embodiment of the present invention. [Figure 7] FIG. 7 is a flowchart defining an operation procedure when the radar device according to the embodiment of the present invention performs detection processing. [Figure 8] FIG. 8 is a diagram conceptually illustrating an example of a transmission wave transmitted by the radar device according to the first modification of the embodiment of the present invention. [Figure 9] FIG. 9 is a diagram conceptually illustrating an example of a transmission wave transmitted by the radar device according to the second modification of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference characters and their description will not be repeated. In addition, at least some of the embodiments described below may be arbitrarily combined.

[0035] <Radar device configuration> Fig. 1 is a diagram showing a configuration of a radar device according to an embodiment of the present invention. Referring to Fig. 1, a radar device 301 includes a radar unit 201 and a display processing unit 202. The radar unit 201 includes a transmission control unit 21, a transmission unit 22, a circulator 23, an antenna 24, a reception unit 25, oscillators 26A and 26B, mixers 27A and 27B, BPFs (Band Pass Filters) 28A and 28B, a delay unit 29, a pulse compression unit 30, and a target detection unit 31. A part or all of the transmission control unit 21, the pulse compression unit 30, the target detection unit 31, and the display processing unit 202 are realized, for example, by a processing circuit including one or more processors.

[0036] The radar device 301 is, for example, a pulse radar device. The radar device 301 is mounted on, for example, a ship. The radar device 301 performs processing to display, on a display device (not shown), an echo image indicating the presence or absence of a target in a detection target area that is an area monitored by the ship, and the distance between the radar device 301 and the target. The ship is an example of a surface vehicle.

[0037] The radar unit 201 outputs echo data indicating the detection result of a target in a detection target area to the display processing unit 202. The radar unit 201 outputs echo data indicating the detection result of a target in a detection target area for each sweep period T to the display processing unit 202.

[0038] The display processing unit 202 performs processing for displaying an echo image in the detection target area on a display device based on the multiple echo data received from the radar unit 201 .

[0039] [Radar section] (Transmitted wave) The transmitting unit 22 transmits pulsed radio waves (hereinafter also referred to as "transmission waves") via the antenna 24. More specifically, the transmitting unit 22 transmits two types of transmission waves, transmission wave E1 and transmission wave E2, during a sweep period T. The transmission wave E1 is an example of a first radio wave, and the transmission wave E2 is an example of a second radio wave.

[0040] Specifically, for example, the transmission control unit 21 outputs a pulsed transmission trigger to the transmission unit 22. For example, the transmission control unit 21 outputs to the transmission unit 22 a transmission trigger Tr1 which is a transmission trigger for generating a transmission wave E1, and a transmission trigger Tr2 which is a transmission trigger for generating a transmission wave E2.

[0041] The transmitter 22 generates a transmission wave in accordance with a transmission trigger received from the transmission control unit 21, and transmits the generated transmission wave to the detection target area via the circulator 23 and the antenna 24. The transmitter 22 includes, for example, a magnetron used to generate the transmission wave. The transmitter 22 generates a transmission wave with a frequency specific to the magnetron. Here, for example, the transmitter 22 includes a magnetron used to generate the transmission wave E1 and a magnetron used to generate the transmission wave E2.

[0042] Specifically, for example, the transmitter 22 generates a sine wave of frequency F1 in X band (X band: 8 GHz to 12 GHz) as the transmission wave E1 during a period corresponding to the pulse width of the transmission trigger Tr1 received from the transmission control unit 21.

[0043] Also, for example, the transmitting unit 22 generates a sine wave of frequency F2 in the same band as frequency F1 as the transmission wave E2 during a period corresponding to the pulse width of the transmission trigger Tr2 received from the transmission control unit 21. For example, the transmitting unit 22 generates a sine wave of frequency F2 in the X band. Frequency F2 is different from frequency F1. This makes it possible to suppress interference between the transmission waves E1 and E2. In this embodiment, for example, frequency F2 is higher than frequency F1.

[0044] The transmitter 22 transmits a transmission wave E1 and a transmission wave E2 to a detection target area at a predetermined pulse repetition interval (PRI).

[0045] The frequency F1 of the transmission wave E1 and the frequency F2 of the transmission wave E2 are not limited to the frequency of the X band, but may be a frequency of another band different from the X band, for example, a frequency of the S band (S band: 2 GHz to 4 GHz).

[0046] FIG. 2 is a conceptual diagram illustrating an example of a transmission wave transmitted by the radar device according to the embodiment of the present invention.

[0047] In Fig. 2, the upper diagram is a diagram showing an example of the waveform of a transmission wave. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram is a diagram showing an example of the change over time in the frequency of a sine wave in a transmission wave. In the lower diagram, the horizontal axis indicates time, and the vertical axis indicates frequency.

[0048] 2, the transmitting unit 22 transmits a transmission wave E1 and then transmits a transmission wave E2. Specifically, for example, the transmitting unit 22 transmits the transmission wave E1 and then transmits the transmission wave E2 successively in time with the transmission wave E1.

[0049] In the example shown in FIG. 2, the transmitting unit 22 transmits a transmission wave E1 in the period from time t1 to time t2. The transmitting unit 22 transmits a transmission wave E2 in the period from time t2 to time t3. In addition, in the example shown in FIG. 2, the pulse width of the transmission wave E1 is the same as the pulse width of the transmission wave E2. Hereinafter, the pulse width of each of the transmission waves E1 and E2 is also referred to as a "pulse width PW1." As an example, the pulse width PW1 is 5 μs. In other words, the transmission period of the transmission waves E1 and E2 in the radar device 301 is 10 μs.

[0050] As described above, in this embodiment, the transmitter 22 transmits the transmission wave E1 and then transmits the transmission wave E2 successively in time with the transmission wave E1. When the pulse width PW1 of the transmission wave E1, i.e., the transmission period of the transmission wave E1, is 5 μs, the difference d between the transmission timing of the transmission wave E1 and the transmission timing of the transmission wave E2 is 5 μs.

[0051] For example, the transmitter 22 transmits a transmission wave whose frequency changes over time. Specifically, for example, in the period of one pulse, the frequency F1 of the transmission wave E1 and the frequency F2 of the transmission wave E2 increase at a constant rate with respect to time.

[0052] 2, the frequency F1 of the transmission wave E1 increases from frequency f11 to frequency f12 in the period from time t1 to time t2. The frequency f11 is, for example, 10 GHz.

[0053] The frequency F2 of the transmission wave E2 increases from frequency f21 to frequency f22 during the period from time t2 to time t3. The frequency f21 is greater than the frequency f12. For example, the difference between the frequency f21 and the frequency f12 is 10 MHz.

[0054] In the example shown in FIG. 2, the rate of change C1 per unit time of the frequency of the transmission wave E1 is the same as the rate of change C2 per unit time of the frequency of the transmission wave E2.

[0055] The frequency F1 of the transmission wave E1 and the frequency F2 of the transmission wave E2 may decrease at a constant rate over time. Also, the frequency F1 of the transmission wave E1 and the frequency F2 of the transmission wave E2 may be constant values ​​that do not change over time.

[0056] (Received signal) Referring back to FIG. 1, the receiver 25 receives, via the antenna 24, a reflected wave that is the result of the transmission wave transmitted from the transmitter 22 being reflected by a target.

[0057] More specifically, for example, the receiving unit 25 receives a receiving signal R1, which is a signal including a reflected wave of the transmission wave E1, via the antenna 24 and the circulator 23. The receiving unit 25 also receives a receiving signal R2, which is a signal including a reflected wave of the transmission wave E2, via the antenna 24 and the circulator 23. The reception period of the receiving signals R1 and R2 in the radar device 301 is, for example, 30 μs. That is, the receiving unit 25 receives a receiving signal R1 based on the transmission wave E1 and a receiving signal R2 based on the transmission wave E2. The receiving signal R1 is an example of a first receiving signal. The receiving signal R2 is an example of a second receiving signal. In the following description, each of the receiving signals R1 and R2 is also referred to as a "receiving signal R."

[0058] FIG. 3 is a diagram conceptually illustrating an example of a reception signal received by the radar device according to the embodiment of the present invention.

[0059] In Fig. 3, the upper diagram is a diagram showing an example of the waveforms of the received signals R1 and R2. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram is a diagram showing an example of the change over time in the frequency of the sine waves in the received signals R1 and R2. In both the upper and lower diagrams, the horizontal axis indicates time, and the vertical axis indicates amplitude.

[0060] 3, the receiving unit 25 cannot receive the receiving signal R1 during the period from time t2 to time t3 when the transmission wave E2 is transmitted, i.e., during the transmission period of the transmission wave E2. The receiving unit 25 receives the receiving signal R1 during a period after the transmission period of the transmission wave E2, for example, during the period from time t4 to time t5. The receiving unit 25 also receives the receiving signal R2 during a period after the reception period of the receiving signal R1, for example, during the period from time t5 to time t6.

[0061] As described above, the pulse width of the transmission wave E1 and the pulse width of the transmission wave E2 are the same pulse width PW1. For simplicity, the pulse width of the reception signal R1 and the pulse width of the reception signal R2 are the same. Hereinafter, the pulse widths of the reception signals R1 and R2 are also referred to as "pulse width PW2." As an example, the pulse width PW2 is 5 μs.

[0062] 3, the frequency of the received signal R1 increases from frequency f11 to frequency f12 during the period from time t4 to time t5, similar to the frequency F1 of the transmitted wave E1. The frequency of the received signal R2 increases from frequency f21 to frequency f22 during the period from time t5 to time t6, similar to the frequency F2 of the transmitted wave E2. The receiving unit 25 outputs the received received signal R to the mixers 27A and 27B.

[0063] 1 again, for example, the oscillator 26A generates a local signal L1 with a frequency fa and outputs the generated local signal L1 to the mixer 27A. The frequency fa is, for example, the same as the frequency F1 of the transmission wave E1. Note that the frequency fa may be different from the frequency F1.

[0064] Also, for example, the oscillator 26B generates a local signal L2 of a frequency fb and outputs the generated local signal L2 to the mixer 27B. The frequency fb is greater than the frequency fa. The frequency fb is, for example, the same as the frequency F2 of the transmission wave E2. Note that the frequency fb may be different from the frequency F2.

[0065] Mixer 27A multiplies received signal R received from receiving unit 25 by local signal L1 received from oscillator 26A, and outputs a signal indicating the multiplication result (hereinafter also referred to as "multiplication result signal Sr1") to BPF 28A.

[0066] Mixer 27B multiplies received signal R received from receiving unit 25 by local signal L2 received from oscillator 26B, and outputs a signal indicating the multiplication result (hereinafter also referred to as "multiplication result signal Sr2") to BPF 28B.

[0067] BPF 28A extracts reception signal R1 corresponding to transmission wave E1 from multiplication result signal Sr1 received from mixer 27A.

[0068] Specifically, for example, BPF28A attenuates components other than a predetermined pass band B1 among the frequency components of multiplication result signal Sr1 received from mixer 27A. For example, the center frequency of BPF28A is frequency F1 of transmission wave E1. BPF28A outputs to delay unit 29 a signal obtained by attenuating components other than the pass band B1 among the frequency components of multiplication result signal Sr1 received from mixer 27A, i.e., a reception signal R1 corresponding to transmission wave E1.

[0069] BPF 28A extracts reception signal R2 corresponding to transmission wave E2 from multiplication result signal Sr2 received from mixer 27B.

[0070] The BPF 28B attenuates frequency components of the multiplication result signal Sr2 received from the mixer 27B that are outside a predetermined pass band B2. For example, the center frequency of the BPF 28B is the frequency F2 of the transmission wave E2. The BPF 28B outputs to the pulse compression unit 30 a signal obtained by attenuating frequency components of the multiplication result signal Sr1 received from the mixer 27B that are outside the pass band B2, i.e., a reception signal R2 corresponding to the transmission wave E2.

[0071] (Delayed signal) The delay unit 29 outputs a signal obtained by delaying the received signal R1 (hereinafter, also referred to as a "delayed signal R11"). For example, the delayed signal R11 is a signal obtained by delaying the received signal R1 by a difference d between the transmission timing of the transmission wave E1 and the transmission timing of the transmission wave E2.

[0072] FIG. 4 is a diagram conceptually illustrating an example of a delayed signal transmitted in a radar device according to an embodiment of the present invention.

[0073] 4, the upper diagram shows the received signal R1 before delay, and the lower diagram shows the delayed signal R11. In the upper and lower diagrams, the horizontal axis shows time, and the vertical axis shows amplitude.

[0074] 4, delay unit 29 delays received signal R1 received from BPF 28A by difference d, and outputs to pulse compressor 30 a delayed signal R11 which is received signal R1 after the delay.

[0075] (Pulse compression processing) FIG. 5 is a diagram for explaining the pulse compression process performed by the radar device according to the embodiment of the present invention.

[0076] 1 and 5, for example, the pulse compressor 30 performs a pulse compression process to compress the pulse width of each of the delayed signal R11 and the received signal R2.

[0077] More specifically, for example, when the pulse compressor 30 receives the delayed signal R11 from the delay unit 29, the pulse compressor 30 compresses the pulse width of the delayed signal R11. Also, for example, the pulse compressor 30 compresses the pulse width of the received signal R2 that has passed through the BPF 28B.

[0078] 5, the upper diagram shows delayed signal R11 after pulse compression processing, and the lower diagram shows received signal R2 after pulse compression processing. The horizontal axis indicates time, and the vertical axis indicates amplitude.

[0079] 5, the delayed signal R11 after pulse compression processing and the received signal R2 after pulse compression processing have a peak at the same time t10.

[0080] 5, the pulse width of the delayed signal R11 after the pulse compression processing is the same as the pulse width of the received signal R2 after the pulse compression processing. Also, the amplitude A1 of the delayed signal R11 after the pulse compression processing is the same as the amplitude A2 of the received signal R2 after the pulse compression processing.

[0081] The pulse compressor 30 outputs the delayed signal R11 and the received signal R2 after the pulse compression process to the target detection unit 31.

[0082] (Detection Processing) The target object detection unit 31 adds the delayed signal R11 and the received signal R2, and performs detection processing to detect a target object based on the result of the addition.

[0083] More specifically, for example, when the target detection unit 31 receives the delayed signal R11 after pulse compression processing and the received signal R2 from the pulse compression unit 30, it generates a sum signal R20 by adding the delayed signal R11 after pulse compression processing and the received signal R2 after compression processing.

[0084] 6 is a diagram showing an example of an added signal generated by the radar device according to the embodiment of the present invention, in which the horizontal axis indicates time and the vertical axis indicates amplitude.

[0085] 6, the sum signal R20 has a peak at time t20 corresponding to time t10. As described above, the amplitude A1 of the delayed signal R11 after pulse compression processing is the same as the amplitude A2 of the received signal R2 after pulse compression processing. Therefore, the amplitude A10 of the sum signal R20 at time t20 is twice the amplitude A1 of the delayed signal R11 after pulse compression processing or the amplitude A2 of the received signal R2 after pulse compression processing. This makes it possible to improve the signal-to-noise ratio of the signal for detecting a target object.

[0086] After generating the sum signal R20, the target object detection unit 31 generates echo data using a value obtained by logarithmically converting the absolute value of the amplitude of the sum signal R20. Then, the target object detection unit 31 outputs the generated echo data to the display processing unit 202.

[0087] Referring back to FIG. 1, the display processing unit 202 performs processing for displaying an echo image in the detection target area on a display device, based on the echo data received from the target object detection unit 31.

[0088] Next, the process performed by the radar device 301 from transmitting the transmission waves E1 and E2 to generating the sum signal R20 will be described using equations.

[0089] The radar device 301 transmits a transmission wave E1 expressed by the following formula (1) and a transmission wave E2 expressed by the following formula (2). As described above, the radar device 301 transmits the transmission wave E2 after transmitting the transmission wave E1.

[0090] In equations (1) and (2), p(t) is an arbitrary transmission signal. d is the difference between the transmission timing of the transmission wave E2 and the transmission timing of the transmission wave E1. j is an imaginary unit. f is the frequency of the transmission wave E1. f+Δf is the frequency of the transmission wave E2. Note that p(t) may be a fixed value. E1=p(t)×exp(-j2πft) ···(1) E2=p(td)×exp(-j2π(f+Δf)t) ···(2)

[0091] The radar device 301 receives a reception signal R1 expressed by the following formula (3) and a reception signal R2 expressed by the following formula (4). Here, the amplitude of the reception signal R1 is the same as the amplitude of the reception signal R2. In formulas (3) and (4), A is the amplitude of each of the reception signals R1 and R2. P is the distance from the ship on which the radar device 301 is mounted to the target. c is the speed of light. Na(t) and Nb(t) are additive noises.

[0092]

number

[0093]

number

[0094] The oscillator 26A outputs a local signal L1 represented by the following equation (5) to the mixer 27A. L1 = exp(-j2πft) (5)

[0095] The oscillator 26B outputs a local signal L2 represented by the following equation (6) to the mixer 27B. L2=exp(-j2π(f+Δf)t) ···(6)

[0096] The mixer 27A multiplies the received signal from the receiver 25 by the local signal L1 from the oscillator 26A, and outputs a multiplication result signal Sr1 indicating the multiplication result to the BPF 28A.

[0097] The BPF 28A extracts a received signal R1 corresponding to the transmission wave E1 from the multiplication result signal Sr1 received from the mixer 27A. The received signal R1 extracted by the BPF 28A is expressed by the following equation (7).

[0098]

number

[0099] The mixer 27B multiplies the received signal from the receiver 25 by the local signal L2 from the oscillator 26B, and outputs a multiplication result signal Sr2 indicating the multiplication result to the BPF 28B.

[0100] The BPF 28B extracts a received signal R2 corresponding to the transmission wave E2 from the multiplication result signal Sr2 received from the mixer 27B. The received signal R2 extracted by the BPF 28B is expressed by the following equation (8).

[0101]

number

[0102] The delay unit 29 delays the received signal R1 that has passed through the BPF 28A by the difference d between the transmission timing of the transmitted wave E2 and the transmission timing of the transmitted wave E2. The delayed signal R11, which is the received signal R1 delayed by the difference d, is expressed by the following equation (9).

[0103]

number

[0104] Here, if the second term on the right side of equation (9) is N1(t), the delayed signal R11 is expressed by the following equation (10).

[0105]

number

[0106] Furthermore, if the second term on the right side of equation (8) is N2(t), then the received signal R2 is expressed by the following equation (11).

[0107]

number

[0108] In equation (11), when Δf is much smaller than f, the received signal R2 is expressed by the following equation (12).

[0109]

number

[0110] The target object detection unit 31 adds together the delayed signal R11 expressed by the formula (10) and the received signal R2 expressed by the formula (12). The added signal R20 indicating the addition result is expressed by the following formula (13).

[0111]

number

[0112] As shown in equation (13), the amplitude of the sum signal R20 is twice the amplitude A of each of the delayed signal R11 and the received signal R2.

[0113] <Operation flow> The radar device according to the embodiment of the present invention includes a computer including a memory, and a processor such as a CPU in the computer reads out from the memory a program including some or all of the steps of the following flowcharts and executes it. The program of this device can be installed from the outside. The program of this device is distributed in a state stored on a recording medium or via a communication line.

[0114] FIG. 7 is a flowchart defining an operation procedure when the radar device according to the embodiment of the present invention performs detection processing.

[0115] 7, first, the radar device 301 transmits a transmission wave E1 having a frequency F1 to a detection target area (step S101).

[0116] Next, the radar device 301 transmits a transmission wave E2 of a frequency F2 different from the frequency F1 to the detection target area. For example, as described above, the radar device 301 transmits the transmission wave E1 and then transmits the transmission wave E2 successively in time with the transmission wave E1 (step S102).

[0117] Next, the radar device 301 receives a reception signal R1 based on the transmission wave E1 (step S103).

[0118] Next, the radar device 301 receives a reception signal R2 based on the transmission wave E2 (step S104).

[0119] Next, the radar device 301 delays the received signal R1 by the difference d between the transmission timing of the transmission wave E1 and the transmission timing of the transmission wave E2 (step S105).

[0120] Next, the radar device 301 performs a pulse compression process to compress the pulse width of the delayed signal R11, which is obtained by delaying the received signal R1 by the difference d, and the pulse width of the received signal R2 (step S106).

[0121] Next, the radar device 301 generates a sum signal R20 by adding the delayed signal R11 after the pulse compression processing and the received signal R2 after the pulse compression processing (step S107).

[0122] Next, the radar device 301 performs a detection process to detect a target based on the generated sum signal R20. For example, as described above, when the radar device 301 generates the sum signal R20, the radar device 301 generates echo data using a value obtained by logarithmically converting the absolute value of the amplitude of the sum signal R20 (step S108).

[0123] Next, the radar device 301 displays an echo image of the detection target area on a display device based on the generated echo data (step S109).

[0124] However, when the number of pulses of radio waves transmitted and received by a radar device increases, the pulse repetition frequency decreases, and the number of pulses that hit a target decreases. In this case, the detection performance of the target may decrease. In addition, since the transmission and reception time of radio waves becomes longer, if there is another ship around the ship on which the radar device 301 is installed, radio wave interference may occur between the radar device 301 and another radar device installed on the other ship.

[0125] In contrast, the radar device 301 according to the embodiment of the present invention can improve the target detection performance by using the above-mentioned configuration and method. Also, in the radar device 301, the transmission period of the transmission waves E1, E2 and the reception period of the reception signal R can be shortened, so that the occurrence of radio wave interference between the radar device 301 and other radar devices existing around the radar device 301 can be suppressed.

[0126] <Variation 1> In the radar device 301, the rate of change of the pulse width and frequency F2 of the transmission wave E2 may be different from the rate of change of the pulse width and frequency F1 of the transmission wave E1, respectively.

[0127] Fig. 8 is a diagram conceptually illustrating an example of a transmission wave transmitted by the first modified example of the radar device according to the embodiment of the present invention. In Fig. 8, the upper diagram is a diagram illustrating an example of a waveform of the transmission wave. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram is a diagram illustrating an example of a change over time in the frequency of a sine wave in the transmission wave. In the lower diagram, the horizontal axis indicates time, and the vertical axis indicates frequency.

[0128] 8, in Modification 1, the pulse width PW11 of the transmission wave E1 is larger than the pulse width PW12 of the transmission wave E2. In the example shown in Fig. 8, the pulse width PW11 is 10 µs, and the pulse width PW12 is 5 µs.

[0129] Also, for example, the variation width D1 of the frequency F1 of the transmission wave E1 is the same as the variation width D2 of the frequency F2 of the transmission wave E2. In the example shown in Fig. 8, the variation width D1 is the difference between the frequency f11 at time t1 and the frequency f12 at time t2. The variation width D2 is the difference between the frequency f21 at time t3 and the frequency f22 at time t4.

[0130] Also, for example, the rate of change C1 per unit time of frequency F1 is different from the rate of change C2 per unit time of frequency F2. In the example shown in Fig. 8, the period from time t1 to time t2 is longer than the period from time t3 to time t4. Therefore, the rate of change C1 is smaller than the rate of change C2.

[0131] <Variation 2> The radar device 301 may be configured to transmit a transmission wave E2 at a predetermined interval G after transmitting a transmission wave E1.

[0132] Fig. 9 is a diagram conceptually illustrating an example of a transmission wave transmitted by the radar device according to the second modification of the embodiment of the present invention. In Fig. 9, the upper diagram is a diagram illustrating an example of a waveform of the transmission wave. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram is a diagram illustrating an example of a change over time in the frequency of a sine wave in the transmission wave. In the lower diagram, the horizontal axis indicates time, and the vertical axis indicates frequency.

[0133] 9, in the second modification, the transmitter 22 transmits the transmission wave E1 during the period from time t21 to time t22, and then starts transmitting the transmission wave E2 at time t23, which is a predetermined time Ta after time t22. For example, the predetermined time Ta is shorter than the pulse width PW1 of each of the transmission waves E1 and E2. The transmitter 22 then transmits the transmission wave E2 during the period from time t23 to time t24.

[0134] The frequency F1 of the transmission wave E1 increases from frequency f11 to frequency f12 in the period from time t21 to time t22. The frequency F2 of the transmission wave E2 increases from frequency f21 to frequency f22 in the period from time t23 to time t24.

[0135] The above-described embodiments should be considered as illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0136] 21 Transmission control section 22 Transmitter 23 Circulator 24 Antenna 25 Receiving section 26A, 26B Oscillator 27A, 27B Mixer 28A, 28B BPF 29 Delay Unit 30 Pulse Compression Section 31 Target Detection Department 201 Radar Section 202 Display processing unit 301 Radar Equipment E1,E2 transmission wave R1, R2 received signal R11 Delay signal

Claims

1. A transmitter that transmits a pulsed radio wave via an antenna; a receiving unit that receives, via the antenna, a reflected wave of the transmitted radio wave reflected by a target; a target detection unit that performs a detection process to detect the target, The transmission unit transmits the second radio wave after transmitting the first radio wave, The target detection unit adds a delayed signal, which is a signal obtained by delaying a first received signal based on the first radio wave, to a second received signal based on the second radio wave, and performs the detection process based on the addition result.

2. 2. The radar device according to claim 1, wherein the delayed signal is a signal obtained by delaying the first received signal by a difference between a transmission timing of the first radio wave and a transmission timing of the second radio wave.

3. 3. The radar device according to claim 1, wherein the transmission unit transmits the second radio wave after transmitting the first radio wave, and the second radio wave is transmitted successively to the first radio wave.

4. 3. The radar device according to claim 1, wherein a pulse width of the first radio wave is the same as a pulse width of the second radio wave.

5. 3. The radar device according to claim 1, wherein a pulse width of the second radio wave is smaller than a pulse width of the first radio wave.

6. The radar device according to claim 5 , wherein the transmission unit transmits the radio waves whose frequency changes over time.

7. 7. The radar device according to claim 6, wherein a change width of the frequency of the first radio wave is the same as a change width of the frequency of the second radio wave.

8. The radar device according to claim 7 , wherein a rate of change of the frequency of the first radio wave is different from a rate of change of the frequency of the second radio wave.

9. The radar device further comprises: a pulse compression unit that performs a pulse compression process to compress a pulse width of each of the delayed signal and the second received signal, a pulse width of the delayed signal after the pulse compression processing is equal to a pulse width of the second received signal after the pulse compression processing; 3. The radar device according to claim 1, wherein the target detection unit performs the detection process based on a result of adding the delayed signal after the pulse compression process and the second received signal after the pulse compression process.

10. A method for detecting a target in a radar device, comprising: A pulsed radio wave is transmitted through an antenna, The transmitted radio wave is reflected by a target and the reflected wave is received via the antenna; performing a detection process for detecting the target; transmitting the second radio wave after transmitting the first radio wave; A target detection method comprising adding a delayed signal, which is a delayed signal of a first received signal based on the first radio wave, to a second received signal based on the second radio wave, and performing the detection processing based on a result of the addition.

11. 11. The target detection method according to claim 10, wherein the delayed signal is a signal obtained by delaying the first received signal by a difference between a transmission timing of the first radio wave and a transmission timing of the second radio wave.

12. 12. The target detection method according to claim 10, further comprising transmitting the second radio wave successively in time to the first radio wave after transmitting the first radio wave.

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