Radar Apparatus and Target Tracking Method

Abstract

A radar apparatus for detecting a target of the present invention, comprising: a transmission module configured to: transmit a first pulsed electromagnetic wave from an antenna; and transmit a second pulsed electromagnetic wave from the antenna after transmitting the first pulsed electromagnetic wave; a receiver configured to receive the first reflected wave reflected at a target and output a first reception signal based on the first reflected wave, and receive the second reflected wave reflected at the target and output a second reception signal based on the second reflected wave; and processing circuitry configured to: delay the first reception signal by a predetermined time, add the second reception signal to the delayed first reception signal, and perform the detection processing based on the added reception signal. (FIG. 1)

Description

Radar Apparatus and Target Tracking Method

[0001] The present invention relates to a radar apparatus and a target detection method.

[0002] A radar apparatus that detects a target using pulsed electromagnetic waves has been developed. For example, Patent Document 1 (Japanese Patent Laid-Open Publication No. 2016-016620) discloses the following radar device. That is, the radar apparatus alternately performs a first detection process for detecting the surroundings by transmitting and receiving a pulse signal for a short distance and transmitting and receiving a pulse signal for a long distance with a pulse width longer than the pulse signal for a short distance, and a second detection process for detecting the surroundings by transmitting and receiving the pulse signal for a long distance.

[0003] Patent Literature: Japanese Patent Laid-Open No. 2016-16620

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

[0005] Generally, it is difficult to receive a reflected signal during a period when a pulsed electromagnetic wave is being transmitted. When an electromagnetic wave with a large pulse width is transmitted in order to improve the signal-to-noise ratio of the reflected signal, the period during which the object cannot be detected is prolonged. Therefore, it is possible to shorten the period during which the object cannot be detected by increasing the type of pulsed electromagnetic wave transmitted and using other electromagnetic waves with a shorter pulse width.

[0006] However, in the radar apparatus, the number of pulses of electromagnetic wave transmitted and received increases, the pulse repetition frequency (PRF) decreases, and thus the number of pulses hitting the object decreases. In this case, the detection performance of the target may decrease.

[0007] The purpose of the present invention is to provide a radar apparatus and a target detecting method capable of improving the detection performance of the target.

[0008] In order to solve the above problem, the radar apparatus for detecting a target of the present invention comprises a transmitter configured to: transmit a first pulsed electromagnetic wave from an antenna; and transmit a second pulsed electromagnetic wave from the antenna after transmitting the first pulsed electromagnetic wave; a receiver configured to receive the first reflected wave reflected at a target and output a first reception signal based on the first reflected wave, and receive the second reflected wave reflected at the target and output a second reception signal based on the second reflected wave. The radar apparatus further comprises processing circuitry configured to: delay the first reception signal by a predetermined time, add the second reception signal to the delayed first reception signal, and perform the detection processing based on the added reception signal.

[0009] In this manner, by using the addition result of the signal obtained by delaying the first reception signal based on the first electromagnetic wave and the second reception signal based on the second electromagnetic wave to detect the target, it is possible to add two received signals in phase. In result, the signal-to-noise ratio of the signal for detecting the target can be improved.

[0010] Moreover, since the transmission interval between the first electromagnetic wave and the second electromagnetic wave can be shortened, the correlation between the two received signals can be enhanced. Therefore, the detection performance of the object can be improved.

[0011] In the radar apparatus, the predetermined time may be the difference between the transmission timing of the first electromagnetic wave and the second transmission timing of the second electromagnetic wave. With such a configuration, the phases of the two received signals to be added can be more accurately matched, and thus the signal-to-noise ratio of the signal for detecting the object can be further improved.

[0012] In the radar apparatus, the frequency of the first electromagnetic wave may be different from the frequency of the second electromagnetic wave.

[0013] Also, the transmitter may transmit the second electromagnetic wave consecutively in time with the first electromagnetic wave after transmitting the first radio wave. With such a configuration, the correlation between the two received signals to be added can be further enhanced, so that the object target can be detected more accurately.

[0014] In the radar apparatus, the pulse width of the first pulsed electromagnetic wave may be the same as the pulse width of the second pulsed electromagnetic wave. With such a configuration, for example, compared with a configuration in which the pulse width of the second electromagnetic wave is larger than the pulse width of the first electromagnetic wave, the transmission period of the electromagnetic wave can be shortened and the reception period of the reflected signal reflected by the target can be shortened in the radar device. In result, it is possible to suppress the occurrence of interference of the electromagnetic wave and the interference of the reflected signal with other radar apparatus existing around the radar device.

[0015] Also, the pulse width of the second pulsed electromagnetic wave may be narrower than the pulse width of the first pulsed electromagnetic wave. With such a configuration, for example, compared with a configuration in which the pulse width of the second electromagnetic wave is larger than the pulse width of the first electromagnetic wave, the transmission period of the electromagnetic wave can be shortened in the radar device, and the reception period of the reflected signal reflected by the target by the electromagnetic wave can be shortened. In the result, it is possible to suppress the occurrence of interference of the electromagnetic wave and the interference of the reflected signal with other radar devices existing around the radar device.

[0016] In addition, during the period in which the pulsed electromagnetic wave is transmitted, the reflected signal reflected by the target cannot be received. As described above, when the first electromagnetic wave and the second electromagnetic wave are transmitted with different pulse widths, the period in which the reflected signal corresponding to the first electromagnetic wave cannot be received can be shortened by making the pulse width of the second electromagnetic wave smaller than the pulse width of the first electromagnetic wave transmitted before the second electromagnetic wave.

[0017] Either the first pulsed electromagnetic wave or the second pulsed electromagnetic wave may change in frequency. Also, both the first pulsed electromagnetic wave and the second pulsed electromagnetic wave may change in frequency. With such a configuration, the transmission power can be reduced, and the circuit configuration can be simplified compared with a configuration that transmits the electromagnetic wave whose frequency is constant.

[0018] In the radar apparatus, the frequency change rate of the first pulsed electromagnetic wave may be the same as the frequency change rate of the second pulsed electromagnetic wave. With such a configuration, for example, when pulse compression processing is performed to compress the pulse width of each of the delay signal and the second reception signal, the pulse width of the delay signal after pulse compression processing and the pulse width of the second reception signal after pulse compression processing can be made the same, so that the delay signal and the second reception signal can be easily added together.

[0019] The frequency change rate of the first pulsed electromagnetic wave may be different from the frequency change rate of the second pulsed electromagnetic wave. For example, in a configuration in which the pulse widths of the first electromagnetic wave and the pulse widths of the second electromagnetic wave are different from each other, the pulse widths of the delay signal and the second received signal are compressed. In order to easily add the delay signal and the second received signal, it is necessary to make the range of change of the frequency of the first electromagnetic wave and the range of change of the frequency of the second electromagnetic wave the same, so that the pulse width of the delay signal after pulse compression processing and the pulse width of the second received signal after pulse compression processing are the same.

[0020] As described above, in a configuration in which the pulse width of the first electromagnetic wave and the pulse width of the second electromagnetic wave are different from each other, the frequency change rate of the first electromagnetic wave is different from the frequency change rate of the second electromagnetic wave, whereby the frequency change rate of the frequency of the first electromagnetic wave and the frequency change rate of the second electromagnetic wave can be adjusted so that the frequency change rate of the first electromagnetic wave is the same as the frequency change rate of the second electromagnetic wave, so that the delay signal and the second received signal can be easily added.

[0021] In the radar apparatus, the processing circuitry may further compress the pulse width of the delay first signal and the second reception signal, wherein the pulse width of the compressed delay first signal is the same as the pulse width of the compressed second reception signal and perform the detection processing based on the added signal obtained by adding the compressed delay signal to the compressed second reception signal.

[0022] In this manner, by the configuration of compressing the pulse width of each of the delay signals and the second reception signal, the signal-to-noise ratio of the signal for detecting the object can be increased by adding the delay signal and the second reception signal. Further, since the pulse width of the delay signal after the pulse compression processing is the same as the pulse width of the second reception signal after the pulse compression processing, the delay signal and the second reception signal can be easily added.

[0023] The radar apparatus of the present invention may further include an oscillator configured to generate a first local signal having a first frequency and a second local signal having a second frequency different from the first frequency. In this configuration, the apparatus further includes a mixer configured to: mix the first local signal to the first reception signal, and the second local signal to the second reception signal, respectively. Also, the apparatus includes a bandpass filter configured to: be inputted the mixed first signal and the mixed second signal, respectively, selectively pass a first signal of a first predetermined frequency and a second signal of a second predetermined frequency, respectively, and output the past first signal to the delay unit and output the past second signal to the pulse compressor, respectively.

[0024] The target tracking method for detecting a target of the present invention comprises: transmitting a first pulsed electromagnetic wave from an antenna; transmitting a second pulsed electromagnetic wave from the antenna after transmitting the first pulsed electromagnetic wave; outputting a first reception signal and a second reception signal, wherein the first reception signal and the second reception signal are reflected waves from a target, respectively; delaying the first reception signal by a predetermined time, adding the second reception signal to the delayed first reception signal, and performing the detection processing based on the added reception signal.

[0025] Thus, by the method of detecting the object using the addition result of the signal obtained by delaying the first reception signal based on the first electromagnetic wave and the second reception signal based on the second electromagnetic wave, two received signals in phase can be added, and thus the signal-to-noise ratio of the signal for detecting the object can be improved. Moreover, since the transmission interval between the first electromagnetic wave and the second electromagnetic wave can be shortened, the correlation between the two received signals can be enhanced. Therefore, the detection performance of the object can be improved.

[0026] In the target tracking method, the predetermined time may be the difference between the transmission timing of the first electromagnetic wave and the second transmission timing of the second electromagnetic wave. Also, the second electromagnetic wave may transmit consecutively in time with the first electromagnetic wave after transmitting the first radio wave. By such a method, the phases of the two received signals to be added can be more accurately matched, and the signal-to-noise ratio of the signals for detecting the object can be further improved.

[0027] With such a configuration, the transmission power can be reduced and the circuit configuration can be simplified compared with a configuration that transmits the electromagnetic wave whose frequency is constant. By such a method, the correlation between the two received signals to be added can be further enhanced, so that the target can be detected more accurately.

[0028] According to the present invention, the detection performance of the target can be improved.

[0029] FIG. 1 is a diagram showing a configuration of a radar apparatus according to an embodiment of the present invention.

[0030] FIG. 2 is a diagram conceptually showing an example of a transmission wave transmitted by a radar apparatus according to an embodiment of the present invention.

[0031] FIG. 3 is a diagram conceptually showing an example of a reception signal received by a radar apparatus according to an embodiment of the present invention.

[0032] FIG. 4 is a diagram conceptually showing an example of a delay signal transmitted by a radar apparatus according to an embodiment of the present invention.

[0033] FIG. 5 is a diagram for explaining pulse compression processing by a radar apparatus according to an embodiment of the present invention.

[0034] FIG. 6 is a diagram showing an example of added signal generated by a radar apparatus according to an embodiment of the present invention.

[0035] FIG. 7 is a flowchart defining an operation procedure when a radar apparatus according to an embodiment of the present invention performs detection processing.

[0036] FIG. 8 is a diagram conceptually showing an example of a transmission wave transmitted by a modification 1 of a radar apparatus according to an embodiment of the present invention.

[0037] FIG. 9 is a diagram conceptually showing an example of a transmission wave transmitted by a modification 2 of a radar apparatus according to an embodiment of the present invention.

[0038] Embodiments of the present invention will now be described with reference to the drawings. The same reference numerals are used for the same or equivalent portions in the drawings, and the description is not repeated. In addition, at least a part of the following embodiments may be optionally combined. (Configuration of radar apparatus)

[0039] 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 apparatus 301 includes a radar 201 and a display 202. The radar 201 includes a transmission controller 21, a transmitter 22, a circulator 23, an antenna 24, a receiver 25, oscillators 26 A and 26B, mixers 27 A and 27B, band pass filters 28A and 28B, a delay unit 29, a pulse compressor 30, and a target detector 31. Some or all of the transmission controller 21, the pulse compressor 30, the target detector 31 and the display 202 are implemented, for example, by a processing circuit (Circuitry) including one or more processors.

[0040] The radar apparatus 301 is, for example, a pulsed radar device. The radar apparatus 301 is arranged on a movable body on the water, for example, vessel. The radar apparatus 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, which is an area monitored by the vessel, and the distance between the radar apparatus 301 and the target. The vessel is an example of a moving object on water.

[0041] The radar 201 outputs echo data indicating the detection result of the object in the detection target area to the display 202. The radar 201 outputs echo data indicating the detection result of the object in the detection target area for each sweep period T to the display 202. The display 202 performs processing to display the echo image in the detection target area on the display device based on the plurality of echo data received from the radar 201. (Transmit wave)

[0042] The transmitter 22 transmits a pulsed electromagnetic wave (Hereinafter also referred to as "transmission wave") via the antenna 24. More specifically, the transmitter 22 transmits two types of transmission waves, transmission wave E1 and transmission wave E2, during the sweep period T. Transmission wave E1 is an example of a first electromagnetic wave, and transmission wave E2 is an example of a second electromagnetic wave.

[0043] Specifically, for example, the transmission controller 21 outputs a pulse transmission trigger to the transmitter 22. For example, the transmission controller 21 outputs the transmission trigger Tr1, which is a transmission trigger for generating the transmission wave E1, and the transmission trigger Tr2, which is a transmission trigger for generating the transmission wave E2, to the transmitter 22.

[0044] In accordance with the transmission trigger received from the transmission controller 21, the transmitter 22 generates a transmission wave 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 for generating the transmission wave. The transmitter 22 generates a transmission wave having a frequency specific to the magnetron. Here, for example, the transmitter 22 includes a magnetron used for generating the transmission wave E1 and a magnetron used for generating the transmission wave E2.

[0045] Specifically, for example, the transmitter 22 generates, as the transmission wave E1, a sinusoidal wave having a frequency F1 of, for example, an X-band (X-band: 8GHz to 12GHz) during a period corresponding to the pulse width of the transmission trigger Tr1 received from the transmission controller 21.

[0046] Also, for example, the transmitter 22 generates, as the transmission wave E2, a sinusoidal wave having a frequency F2 of the same band as the frequency F1 during a period corresponding to the pulse width of the transmission trigger Tr2 received from the transmission controller 21. For example, the transmitter 22 generates a sinusoidal wave having a frequency F2 of the X-band. The frequency F2 is different from the frequency F1. Thus, the interference of transmission waves E1 and E2 can be suppressed. In this embodiment, for example, the frequency F2 is larger than the frequency F1.

[0047] The transmitter 22 transmits transmission wave E1 and transmission wave E2 to the detection target area at a predetermined pulse repetition period (PRI: Pulse Repetition Interval). 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 the frequency of another band different from the X band, for example, the frequency of the S band (S band: 2 GHz to 4 GHz).

[0048] FIG. 2 is a conceptual diagram showing an example of a transmission wave transmitted by a radar apparatus according to an embodiment of the present invention. FIG. 2 shows an example of a waveform of a transmission wave. In the upper FIG. of FIG. 2, the horizontal axis indicates time, and the vertical axis indicates amplitude of the transmission wave. The lower FIG. of FIG. 2 shows an example of the frequency change over time of a sine wave in a transmission wave. The horizontal axis indicates time, and the vertical axis indicates frequency.

[0049] The transmitter 22 transmits transmission wave E2 after transmitting transmission wave E1. Specifically, for example, the transmitter 22 transmits transmission wave E2 consecutively in time with transmission wave E1 after transmitting transmission wave E1.

[0050] In the example shown in FIG. 2, the transmitter 22 transmits transmission wave E1 in the period from time t1 to time t2. The transmitter 22 transmits transmission wave E2 in the period from time t2 to time t3. In the example shown in FIG. 2, the pulse width of transmission wave E1 and the pulse width of transmission wave E2 are the same. Hereinafter, the respective pulse widths of transmission wave E1 and transmission wave E2 are also referred to as “pulse width PW1”. As an example, the pulse width PW1 is 5 μs. That is, the transmission period of the transmission waves E1 and E2 in the radar apparatus 301 is 10μs.

[0051] As described above, in the present embodiment, after transmitting the transmission wave E1, the transmitter 22 transmits the transmission wave E2 consecutively 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.

[0052] For example, the transmitter 22 transmits a transmission wave whose frequency changes in time. Specifically, for example, in a 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.

[0053] In the example shown in FIG. 2, the frequency F1 of the transmission wave E1 increases from the frequency f11 to the frequency f12 in the period from the time t1 to the time t2. The frequency f11 is, for example, 10 GHz. The frequency F2 of the transmission wave E2 increases from the frequency f21 to the frequency f22 in the period from the time t2 to the time t3. The frequency f21 is larger than the frequency f12. For example, the difference between the frequency f21 and the frequency f12 is 10MHz.

[0054] In the example shown in FIG. 2, the change rate C1 per unit time of the frequency of the transmission wave E1 and the change rate C2 per unit time of the frequency of the transmission wave E2 are the same. Note that the frequency F1 of the transmission wave E1 and the frequency F2 of the transmission wave E2 may decrease at a constant rate with respect to time. 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 in time. (Reception signal)

[0055] Referring again to FIG. 1, the receiver 25 receives, via the antenna 24, the reflected wave reflected at the target by the transmitted wave transmitted from the transmitter 22.

[0056] More specifically, for example, the receiver 25 receives, via the antenna 24 and the circulator 23, the received signal R1, which is a signal containing the reflected wave of the transmission wave E1. The receiver 25 also receives, via the antenna 24 and the circulator 23, the received signal R2, which is a signal containing the reflected wave of the transmission wave E2. The reception period of the received signals R1 and R2 in the radar apparatus 301 is, for example, 30μs. That is, the receiver 25 receives the received signal R1 based on the transmission wave E1 and the received signal R2 based on the transmission wave E2. The received signal R1 is an example of the first received signal. The reception signal R2 is an example of the second reception signal. In the following description, each of the reception signal R1 and the reception signal R2 is also referred to as the “reception signal R”.

[0057] FIG. 3 is a diagram conceptually showing an example of a reception signal received by a radar apparatus according to an embodiment of the present invention.

[0058] In FIG. 3, the upper diagram is a diagram showing an example of waveforms of reception signals R1 and R2. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram shows an example of the frequency change over time of the sine wave in the received signals R1 and R2. In the upper and lower diagrams, the horizontal axis indicates time and the vertical axis indicates amplitude.

[0059] Referring to FIG. 3, the receiver 25 cannot receive the received signal R1 in the period from the time t2 at which the transmission wave E2 is transmitted to the time t3, that is, the transmission period of the transmission wave E2. The receiver 25 receives the received signal R1 in the period after the transmission period of the transmission wave E2, for example, from the time t4 to the time t5. The receiver 25 receives the received signal R2 in the period after the reception period of the received signal R1, for example, from the time t5 to the time t6.

[0060] As described above, the pulse width of the transmission wave E1 and the pulse width of the transmission wave E2 have the same pulse width PW1. In order to simplify the explanation, 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 signal R1 and the reception signal R2 are also referred to as “pulse width PW2”. As an example, the pulse width PW2 is 5μs.

[0061] In the example shown in FIG. 3, the frequency of the received signal R1 increases from the frequency f11 to the frequency f12 in the same manner as the frequency F1 of the transmission wave E1 in the period from the time t4 to the time t5. The frequency of the received signal R2 increases from the frequency f21 to the frequency f22 in the same manner as the frequency F2 of the transmission wave E2 during the period from the time t5 to the time t6. The receiver 25 outputs the received signal R to the mixers 27A and 27B.

[0062] Referring again to FIG. 1, for example, the oscillator 26A generates a local signal L1 having a frequency fa and outputs the generated local signal L1 to the mixer 27A. The frequency fa is the same as, for example, the frequency F1 of the transmission wave E1. The frequency fa may be different from the frequency F1. For example, the oscillator 26B generates a local signal L2 having the 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 transmission wave E2. The frequency fb may be different from the frequency F2.

[0063] The mixer 27A multiplies the received signal R received from the receiver 25 and the local signal L1 received from the oscillator 26A, and outputs a signal (Hereinafter also referred to as “multiplication result signal Sr1”) indicating the multiplication result to the BPF 28A. The mixer 27B multiplies the received signal R received from the receiver 25 and the local signal L2 received from the oscillator 26B and outputs a signal (Hereinafter also referred to as “multiplication result signal Sr2”) indicating the multiplication result to the BPF 28B.

[0064] The BPF 28A extracts the received signal R1 corresponding to the transmission wave E1 from the multiplication result signal Sr1 received from the mixer 27A.

[0065] Specifically, for example, the BPF 28A attenuates the components other than the predetermined passband B1 among the frequency components of the multiplication result signal Sr1 received from the mixer 27A. For example, the center frequency of the BPF 28A is the frequency F1 of the transmission wave E1. The BPF 28A outputs to the delay unit 29 a signal obtained by attenuating a component other than the passband B1 among the frequency components of the multiplication result signal Sr1 received from the mixer 27A, that is, a received signal R1 corresponding to the transmission wave E1.

[0066] The BPF 28A extracts the received signal R2 corresponding to the transmission wave E2 from the multiplication result signal Sr2 received from the mixer 27B. The BPF 28B attenuates the components other than the predetermined passband B2 among the frequency components of the multiplication result signal Sr2 received from the mixer 27B. 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 compressor 30 a signal obtained by attenuating a component other than the passband B2 out of the frequency component of the multiplication result signal Sr1 received from the mixer 27B, that is, a received signal R2 corresponding to the transmission wave E2. (Delayed signal)

[0067] The delay unit 29 outputs a signal (Hereinafter also referred to as “delayed signal R11”) obtained by delaying the reception signal R1. 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.

[0068] FIG. 4 is a conceptual diagram showing an example of a delay signal transmitted in a radar apparatus according to an embodiment of the present invention.

[0069] In FIG. 4, the upper diagram shows a received signal R1 before a delay. The lower diagram shows a delayed signal R11. In the upper and lower diagrams, the horizontal axis indicates time and the vertical axis indicates amplitude. The delay unit 29 delays the received signal R1 received from the BPF 28A by a difference d, and outputs the delayed signal R11, which is the received signal R1 after the delay, to the pulse compressor 30. (Pulse Compression Processing)

[0070] FIG. 5 is a diagram for explaining pulse compression processing by a radar apparatus according to an embodiment of the present invention.

[0071] Referring to FIGs. 1 and 5, for example, the pulse compressor 30 performs pulse compression processing for compressing the pulse widths of each of the delayed signal R11 and the received signal R2. More specifically, for example, when the pulse compressor 30 receives the delayed signal R11 from the delay unit 29, it 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.

[0072] FIG. 5 shows the delayed signal R11 after pulse compression processing. FIG. 5 shows the received signal R2 after pulse compression processing. The horizontal axis indicates time, and the vertical axis indicates amplitude. The delayed signal R11 after pulse compression processing and the received signal R2 after pulse compression processing have peaks at the same time t10.

[0073] In the example shown in FIG. 5, the pulse width of the delayed signal R11 after pulse compression processing and the pulse width of the received signal R2 after pulse compression processing are the same. In addition, the amplitude A1 of the delayed signal R11 after pulse compression processing and the amplitude A2 of the received signal R2 after pulse compression processing are the same. The pulse compressor 30 outputs the delayed signal R11 and the received signal R2 after pulse compression processing to the target detector 31. (Detection Processing)

[0074] The target detector 31 adds the delayed signal R11 to the received signal R2 and performs detection processing for detecting the object target based on the addition result. More specifically, for example, when the target detector 31 receives the delayed signal R11 and the received signal R2 after pulse compression processing from the pulse compressor 30, it generates the added signal R20 obtained by adding the delayed signal R11 after pulse compression processing and the received signal R2 after compression processing.

[0075] FIG. 6 is a diagram showing an example of an added signal generated by a radar apparatus according to an embodiment of the present invention. The horizontal axis indicates time, and the vertical axis indicates amplitude. The added signal R20 has a peak at time t20 corresponding to time t10. As described above, the amplitude A1 of delayed signal R11 after pulse compression processing and the amplitude A2 of received signal R2 after pulse compression processing are the same. Therefore, the amplitude A10 of added signal R20 at time t20 is twice the amplitude A1 of delayed signal R11 after pulse compression processing or the amplitude A2 of received signal R2 after pulse compression processing. Thus, the signal-to-noise ratio of the signal for detecting the object target can be improved.

[0076] When the target detector 31 generates the added signal R20, it generates echo data using the log-transformed absolute value of the amplitude of the added signal R20. Then, the target detector 31 outputs the generated echo data to the display 202. Referring again to FIG. 1, the display 202 performs processing to display the echo image in the detection target area on the display device based on the echo data received from the target detector 31.

[0077] Next, the processing from the time the radar apparatus 301 transmits the transmission waves E1 and E2 to the time when the added signal R20 is generated will be described using an expression. The radar apparatus 301 transmits the transmission wave E1 represented by the following equation (1) and the transmission wave E2 represented by the following equation (2). As described above, radar apparatus 301 transmits transmission wave E2 after transmitting transmission wave E1.

[0078] In equations (1) and (2), p (t) is an arbitrary transmission signal. The character “d” is the difference between the transmission timing of transmission wave E2 and the transmission timing of transmission wave E1. The character “j” is an imaginary unit and “f” is the frequency of transmission wave E1. “f+Δf” is the frequency of transmission wave E2. Note that p (t) may be a fixed value.

[0079] The radar apparatus 301 receives the reception signal R1 represented by the following equation (3) and the reception signal R2 represented by the following equation (4). Here, the amplitude of the reception signal R1 and the amplitude of the reception signal R2 are the same. In equations (3) and (4), “A” is the amplitude of each of the reception signal R1 and the reception signal R2. The character “P” is the distance from the vessel on which the radar apparatus 301 is mounted to the target. The character “c” is the speed of light. Na (t) and Nb (t) are additional noise.

[0080] The oscillator 26 A outputs the local signal L1 represented by the following equation (5) to the mixer 27 A.

[0081] The oscillator 26B outputs the local signal L2 represented by the following equation (6) to the mixer 27B.

[0082] The mixer 27A multiplies the received signal from the receiver 25 and the local signal L1 from the oscillator 26A, and outputs the multiplication result signal Sr1 indicating the multiplication result to the BPF 28A.

[0083] The BPF 28A extracts the reception signal R1 corresponding to the transmission wave E1 from the multiplication result signal Sr1 received from the mixer 27A. The reception signal R1 extracted by the BPF 28A is represented by the following equation (7).

[0084] The mixer 27B multiplies the received signal from the receiver 25 and the local signal L2 from the oscillator 26B, and outputs the multiplication result signal Sr2 indicating the multiplication result to the BPF 28B.

[0085] The BPF 28B extracts the reception 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 represented by the following equation (8).

[0086] The delay unit 29 delays the received signal R1 that has passed through the BPF 28A by a difference d between the transmission timing of the transmission wave E2 and the transmission timing of the transmission wave E2. The delayed signal R11 for which the received signal R1 has been delayed by a difference d is represented by the following equation (9).

[0087] Here, when the second term on the right-hand side of Equation (9) is N1(t), the delayed signal R11 is expressed by Equation (10) below.

[0088] When the second term on the right-hand side of Equation (8) is N2(t), the received signal R2 is represented by Equation (11) below.

[0089] In Equation (11), when Δf is much smaller than f, the received signal R2 is represented by Equation (12) below.

[0090] The target detector 31 adds the delayed signal R11 represented by the expression (10) and the received signal R2 represented by the expression (12). The added signal R20 representing the addition result is represented by the following expression (13).

[0091] As shown in Equation (13), the amplitude of added signal R20 is twice the amplitude A of each of the delayed signal R11 and the received signal R2. (Flow of operation)

[0092] A radar apparatus according to an embodiment of the present invention is provided with a computer including a memory, and a processor such as a CPU in the computer reads and executes a program including part or all of the steps of the following flowchart from the memory. The program of this device can be installed externally. The program of this device is distributed in a state stored in a recording medium or through a communication line.

[0093] FIG. 7 is a flowchart defining an operation procedure when a radar device according to an embodiment of the present invention performs detection processing. The radar apparatus 301 first transmits transmission wave E1 of frequency F1 to the detection target area (step S101).

[0094] Next, the radar apparatus 301 transmits transmission wave E2 of frequency F2 different from frequency F1 to the detection target area. For example, as described above, the radar apparatus 301 transmits transmission wave E1 and then transmits transmission wave E2 consecutively in time (step S102).

[0095] Next, the radar apparatus 301 receives the reception signal R1 based on the transmission wave E1 (step S103).

[0096] Next, the radar apparatus 301 receives the reception signal R2 based on the transmission wave E2 (step S104).

[0097] Next, the radar apparatus 301 delays the received reception signal R1 by a difference d between the transmission timing of the transmission wave E1 and the transmission timing of the transmission wave E2 (step S105).

[0098] Next, the radar apparatus 301 performs pulse compression processing to compress the pulse width of the delayed signal R11, in which the reception signal R1 is delayed by a difference d, and the pulse width of the reception signal R2 (step S106).

[0099] Next, the radar apparatus 301 generates the added signal R20 obtained by adding the delayed signal R11 after pulse compression processing and the reception signal R2 after pulse compression processing (step S107).

[0100] Next, the radar apparatus 301 performs detection processing for detecting the object target based on the generated added signal R20. For example, as described above, when the radar apparatus 301 generates the added signal R20, it generates echo data using the value obtained by logarithmically transforming the absolute value of the amplitude of the added signal R20 (step S108).

[0101] Next, the radar apparatus 301 displays an echo image in the area to be detected on the display device based on the generated echo data (step S109).

[0102] By the way, when the number of pulses of electromagnetic wave transmitted and received by the radar apparatus increases, the pulse repetition frequency decreases, so that the number of pulses hitting the target decreases. In this case, the detection performance of the target may decrease. In addition, since the transmission / reception time of the electromagnetic wave is prolonged, an interference of the electromagnetic wave with another radar apparatus arranged on another vessel may occur when there is another vessel around the vessel on which the radar apparatus 301 is arranged.

[0103] On the other hand, in the radar apparatus 301 according to the embodiment of the present invention, the detection performance of the object can be improved by the structure and method described above. Since the transmission period of the transmission waves E1 and E2 and the reception period of the reception signal R can be shortened in the radar apparatus 301, the occurrence of interference of electromagnetic waves with other radar devices existing around the radar apparatus 301 can be suppressed. (Example 2)

[0104] In the radar apparatus 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.

[0105] FIG. 8 is a diagram conceptually showing an example of a transmission wave transmitted by the modified example 1 of the radar apparatus according to the embodiment of the present invention. In FIG. 8, the upper diagram is a diagram showing axis indicates time, and the vertical axis indicates amplitude. The lower diagram shows an example of the frequency change over time of a sine wave in a transmission wave. In the lower diagram, the horizontal axis indicates time, and the vertical axis indicates frequency.

[0106] In the modified example 1, the pulse width PW11 of transmission wave E1 is larger than the pulse width PW12 of transmission wave E2. In the example shown in FIG. 8, the pulse width PW11 is 10μs, and the pulse width PW12 is 5μs.

[0107] For example, the change width D1 of the frequency F1 of the transmission wave E1 and the change width D2 of the frequency F2 of the transmission wave E2 are the same. In the example shown in FIG. 8, the change width D1 is the difference between the frequency f11 at time t1 and the frequency f12 at time t2. The change width D2 is the difference between the frequency f21 at time t3 and the frequency f22 at time t4.

[0108] For example, the change rate C1 per unit time of the frequency F1 is different from the change rate C2 per unit time of the 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 change rate C1 is smaller than the change rate C2. (Example 3)

[0109] The radar apparatus 301 may be configured to transmit transmission wave E2 at a predetermined interval G after transmitting transmission wave E1.

[0110] FIG. 9 is a diagram conceptually showing an example of a transmission wave transmitted by a modification 2 of a radar apparatus according to an embodiment of the present invention. In FIG. 9, the upper diagram shows an example of a waveform of a transmission wave. In the upper diagram, the horizontal axis indicates time, and the vertical axis indicates amplitude. The lower diagram shows an example of the frequency change over time of a sine wave in a transmission wave. In the lower diagram, the horizontal axis indicates time, and the vertical axis indicates frequency.

[0111] In the modified example 2, after transmitting the transmission wave E1 in the period from time t21 to time t22, the transmitter 22 starts transmitting the transmission wave E2 at time t23 when a predetermined time Ta has elapsed from time t22. For example, the predetermined time Ta is shorter than the respective pulse widths PW1 of the transmission wave E1 and the transmission wave E2. Then, the transmitter 22 transmits the transmission wave E2 during the period from the time t23 to the time t24.

[0112] The frequency F1 of the transmission wave E1 increases from the frequency f11 to the frequency f12 during the period from the time t21 to the time t22. The frequency F2 of the transmission wave E2 increases from the frequency f21 to the frequency f22 during the period from the time t23 to the time t24.

[0113] The above embodiments should be considered to be illustrative and not restrictive in all respects. It is intended that the scope of the present invention be indicated by the claims rather than the above description and include all changes within the meaning and scope of the claims and equivalence.

[0114] 21 transmission controllers 22 transmitters 23 circulators 24 antennas 25 receivers 26A, 26B oscillators 27A, 27B mixers 28A, 28B BPF (Band Pass Filter) 29 delay units 30 pulse compressors 31 target detectors 201 radars 202 displays 301 radar apparatus E1, E2 transmission waves R1, R2 reception signals R11 delayed signals

Claims

1. A radar apparatus for detecting a target, comprising: a transmitter configured to: transmit a first pulsed electromagnetic wave from an antenna; and transmit a second pulsed electromagnetic wave from the antenna after transmitting the first pulsed electromagnetic wave; a receiver configured to: receive the first reflected wave reflected at a target and output a first reception signal based on the first reflected wave, and receive the second reflected wave reflected at the target and output a second reception signal based on the second reflected wave; and processing circuitry configured to: delay the first reception signal by a predetermined time, add the second reception signal to the delayed first reception signal, and perform the detection processing based on the added reception signal.

2. The radar apparatus according to claim 1, wherein: the predetermined time is the difference between the transmission timing of the first electromagnetic wave and the second transmission timing of the second electromagnetic wave.

3. The radar apparatus according to claim 2, wherein: the frequency of the first electromagnetic wave is different from the frequency of the second electromagnetic wave.

4. The radar apparatus according to any of claim 1 to 3, wherein: the transmitter configured to transmit the second electromagnetic wave consecutively in time with the first electromagnetic wave after transmitting the first radio wave.

5. The radar apparatus according to claim 4, wherein: the pulse width of the first pulsed electromagnetic wave is the same as the pulse width of the second pulsed electromagnetic wave.

6. The radar apparatus according to claim 4, wherein: the pulse width of the second pulsed electromagnetic wave is narrower than the pulse width of the first pulsed electromagnetic wave.

7. The radar apparatus according to claim 4, wherein: either the first pulsed electromagnetic wave or the second pulsed electromagnetic wave changes in frequency.

8. The radar apparatus according to claim 4, wherein: both the first pulsed electromagnetic wave and the second pulsed electromagnetic wave change in frequency.

9. The radar apparatus according to claim 8, wherein: the frequency change rate of the first pulsed electromagnetic wave is the same as the frequency change rate of the second pulsed electromagnetic wave.

10. The radar apparatus according to claim 8, wherein: the frequency change rate of the first pulsed electromagnetic wave is different from the frequency change rate of the second pulsed electromagnetic wave.

11. The radar apparatus according to claim 4, wherein: the processing circuitry further configured to: compress the pulse width of the delay first signal and the second reception signal, wherein the pulse width of the compressed delay first signal is the same as the pulse width of the compressed second reception signal; and perform the detection processing based on the added signal obtained by adding the compressed delay signal to the compressed second reception signal.

12. The radar apparatus according to claim 11, further comprising: an oscillator configured to: generate a first local signal having a first frequency, and a second local signal having a second frequency different from the first frequency; and a mixer configured to: mix the first local signal to the first reception signal, and the second local signal to the second reception signal, respectively, a bandpass filter configured to: be inputted the mixed first signal and the mixed second signal, respectively, selectively pass a first signal of a first predetermined frequency and a second signal of a second predetermined frequency, respectively, and output the past first signal to the delay unit, and output the past second signal to the pulse compressor, respectively.

13. A target tracking method for detecting a target, comprising: transmitting a first pulsed electromagnetic wave from an antenna; transmitting a second pulsed electromagnetic wave from the antenna after transmitting the first pulsed electromagnetic wave; outputting a first reception signal and a second reception signal, wherein the first reception signal and the second reception signal are reflected waves from a target, respectively; delaying the first reception signal by a predetermined time, adding the second reception signal to the delayed first reception signal, and performing the detection processing based on the added reception signal.

14. The target tracking method according to claim 13, wherein: the predetermined time is the difference between the transmission timing of the first electromagnetic wave and the second transmission timing of the second electromagnetic wave.

15. The target tracking method according to claim 13 or 14, wherein: the second electromagnetic wave is transmitted consecutively in time with the first electromagnetic wave after transmitting the first radio wave.

Images