GB2590303A

GB2590303A - Radar device and target distance measurement method

Info

Publication number: GB2590303A
Application number: GB2101539.1A
Authority: GB
Inventors: Kageme Satoshi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-09-13
Filing date: 2018-09-13
Publication date: 2021-06-23
Anticipated expiration: 2038-09-13
Also published as: GB202101539D0; JP6567220B1; JPWO2020054031A1; WO2020054031A1; GB2590303B

Abstract

This radar device (1) emits, to a space, a transmission signal on which in-pulse modulation is executed, performs gate processing in which a plurality of reception gates are set for a received signal generated on the basis of the transmission signal reflected by a target in the space, performs a demodulation process on a signal after the gate processing, performs frequency domain transform on a signal after the demodulation process, detects a target candidate on the basis of the intensity of a frequency domain signal, and calculates the distance to the target candidate.

Description

DESCRIPTION

TITLE OF INVENTION: RADAR DEVICE AN) TARGET DISTANCE

MEASUREMENT METHOD

TECHNICAL FIELD

[0001] The present invention relates to a radar device that measures target distances and a target distance measurement method.

BACKGROUND ART

[0002] For example, a radar device described in Patent Literature 1 radiates a transmission radio-frequency signal into the air, and receives the transmission radio-frequency signal reflected by a target. The conventional radar device generates a sum signal and a difference signal by setting reception gates with different gate widths for a reception radio-frequency signal, and measures a target distance using a discrimination pattern indicating a relationship between the ratio between the sum signal and the difference signal and the distance to the target (hereinafter, referred to as target distance).

CITATION LIST

PATENT LI1ERATURE [0003] Patent Literature 1: JP S60-164275 A

SUMMARY OF INVENTION TECHNICAL PROBLEM

[0004] The conventional radar device described in Patent Literature 1 has a problem that when there are a plurality of targets in a reception gate, since a discrimination pattern varies between conditions of the plurality of targets (e.g., a difference in amplitude between the targets or distance between the targets), target distances of each of the plurality of targets are erroneously measured [0005] The present invention is made to solve the above-described problem, and an object of the present invention is to obtain a radar device and a target distance measurement method that can accurately measure target distances even when there are a plurality of targets in a reception gate.

SOLUTION TO PROBLEM

[0006] A radar device according to the present invention includes a transmitting unit, a receiving unit, a gate processing unit, a demodulation processing unit, a target candidate detecting unit, and a target candidate distance calculating unit. The transmitting unit outputs a transmission signal having been subjected to intra-pulse modulation The receiving unit generates a reception signal on the basis of the transmission signal reflected by a target in space. The gate processing unit performs a gate process in which a plurality of reception gates are set, on the reception signal to generate signals having been subjected to the gate process. The demodulation processing unit performs a demodulation process on the signals having been subjected to the gate process on the basis of the intra-pulse modulation, to generate signals having been subjected to the demodulation process. The frequency-domain transforming unit performs a frequency-domain transform on the signals having been subjected to the demodulation process, to generate frequency-domain signals. The target candidate detecting unit detects a target candidate on the basis of strength of the frequency-domain signals. The target candidate distance calculating unit calculates a distance to the target candidate detected by the target candidate detecting unit.

ADVANTAGEOUS EFFECTS OF INVENTION

[0007] According to the present invention, a transmission signal having been subjected to intra-pulse modulation is radiated into space, a gate process in which a plurality of reception gates are set is performed on a reception signal generated on the basis of the transmission signal reflected by a target in space, a demodulation process is performed on signals having been subjected to the gate process, a frequency-domain transform is performed on signals having been subjected to the demodulation process, a target candidate is detected on the basis of the strength of frequency-domain signals, and a distance to the target candidate is calculated By this configuration, even when there are a plurality of targets in a reception gate, target distances can be accurately measured.

BRIEF DESCRIPTION OF DRAWINGS

[0008] FIG. 1 is a block diagram showing a configuration of a radar device according to a first embodiment FIG. 2 is a block diagram showing a configuration of a transmitting unit of the first embodiment.

FIG. 3 is a block diagram showing a configuration of a receiving unit of the first embodiment.

FIG. 4A is a block diagram showing a hardware configuration that implements functions of the radar device according to the first embodiment, and FIG. 4B is a block diagram showing a hardware configuration that executes software that implements the functions of the radar device according to the first embodiment.

FIG. 5 is a flowchart showing operations of the radar device according to the first embodiment.

FIG. 6A is a schematic diagram showing an overview of processes performed by a signal processing unit in the first embodiment, FIG. 6B is a diagram showing frequency-domain signals corresponding to a plurality of targets with the same velocity v, FIG. 6C is a diagram showing the waveform in a gate number direction of a frequency-domain signal corresponding to a target with the velocity v, and FIG. 6D is a diagram showing the waveform in a distance direction of a signal having been subjected to an inverse frequency-domain transforming process and corresponding to the target with the velocity v FIG. 7 is a flowchart showing operations of the transmitting unit in the first embodiment.

FIG. 8 is a diagram showing a waveform of a transmission RF signal.

FIG. 9 is a flowchart showing operations of the receiving unit in the first embodiment, FIG. 10 is a diagram showing a waveform of a reception video signal.

FIG. 11 is a flowchart showing operations of the signal processing unit in the first embodiment.

FIG. 12 is a diagram showing a relationship between a reception gate with a gate number no and a sampling number m'.

FIG. 13A is a diagram showing a waveform of a reception video signal, FIG. 13B is a diagram showing a waveform of a signal having been subjected to a gate process and corresponding to a reception gate G6, FIG. I3C is a diagram showing a waveform of a signal subjected to a gate process and corresponding to a reception gate G7, and FIG. 13D is a diagram showing a waveform of a signal having been subjected to a gate process and corresponding to a reception gate G8.

FIG. 14A is a diagram showing the waveform of the reception video signal, FIG. 14B is a diagram showing a waveform of a signal having been subjected to a demodulation process and corresponding to the reception gate G6, FIG. 14C is a diagram showing a waveform of a signal having been subjected to a demodulation process and corresponding to the reception gate G7, and FIG. 14D is a diagram showing a waveform of a signal having been subjected to a demodulation process and corresponding to the reception gate G8.

FIG. 15A is a diagram showing the waveforms of the measured values of frequency-domain signals corresponding to a plurality of targets with the same velocity present in reception gates for a case in which a transmission signal has not been subjected to intra-pulse modulation, FIG. 15B is a diagram showing the waveforms of frequency-domain signals for each of the targets with the same velocity present in reception gates for a case in which a transmission signal has not been subjected to intrapulse modulation, FIG. 15C is a diagram showing the waveforms of the measured values of frequency-domain signals corresponding to a plurality of targets with the same velocity present in reception gates for a case in which a transmission signal has been subjected to intra-pulse modulation, and FIG. 15D is a diagram showing the waveforms of frequency-domain signals for each of the targets with the same velocity present in reception gates for a case in which a transmission signal has been subjected to intrapulse modulation.

FIG. 16A is a diagram showing the waveform of the reception video signal, FIG. 16B is a diagram showing the waveforms in the gate number direction of the measured values of frequency-domain signals for each of targets with the same velocity present in reception gates for a case in which a transmission signal has not been subjected to intra-pulse modulation, and FIG. 16C is a diagram showing the waveforms in the gate number direction of the measured values of frequency-domain signals for each of targets with the same velocity present in reception gates for a case in which a transmission signal has been subjected to intra-pulse modulation.

FIG. 17A is a diagram showing the waveforms of frequency-domain signals corresponding to each of targets with the same velocity present in reception gates, and FIG. 17B is a diagram showing the waveforms of signals having been subjected to an inverse frequency-domain transforming process and corresponding to each of targets with the same velocity present in reception gates.

DESCRIPTION OF EMBODIMENTS

[0009] First Embodiment FIG. 1 is a block diagram showing a configuration of a radar device 1 according to a first embodiment The radar device 1 radiates a transmission radio-frequency signal (hereinafter, referred to as a transmission RF signal) having been subjected to intra-pulse modulation into space, receives the transmission RF signal reflected by targets in space, as a reception radio-frequency signal (hereinafter, referred to as a reception RF signal), and calculates distances to target candidates that can serve as observation targets, on the basis of a reception video signal generated from the reception RF signal.

[0010] As shown in FIG. 1, the radar device 1 includes an antenna 2, a transmitting unit 3, a transmission and reception switching unit 4, a receiving unit 5, a signal processing unit 6, and a display 7 The signal processing unit 6 includes a gate processing unit 60, a demodulation processing unit 61, a filter processing unit 62, a frequency-domain transforming unit 63, a high accuracy achievement processing unit 64, a target candidate detecting unit 65, and a target candidate distance calculating unit 66. Note that the signal processing unit 6 may omit one or both of the filter processing unit 62 and the high accuracy achievement processing unit 64 [0011] The antenna 2 radiates a transmission RF signal inputted from the transmission and reception switching unit 4 into space. The transmitting unit 3 outputs a transmission RF signal having been subjected to intra-pulse modulation to the transmission and reception switching unit 4. The transmission and reception switching unit 4 switches between an output of a transmission RF signal from the transmitting unit 3 to the antenna 2 and an output of a reception RF signal from the antenna 2 to the receiving unit 5 at timing set by the transmitting unit 3 [0012] A reflected wave of a transmission RF signal reflected by targets in space enters and is received by the antenna 2. The receiving unit 5 receives a reception RF signal received by the antenna 2, and generates a reception video signal on the basis of the reception RF signal. The signal processing unit 6 calculates distances to target candidates on the basis of the reception video signal inputted from the receiving unit 5, and outputs the calculated distances to the target candidates to the display 7. The display 7 displays information about the distances to the target candidates. The information about the distances to the target candidates includes, for example, target numbers set for each of target candidates and information indicating the distances to the target candidates from the radar device 1.

[0013] The gate processing unit 60 receives a reception video signal from the receiving unit 5, and performs a gate process in which a plurality of reception gates are set, on the reception video signal and thereby generates signals having been subjected to the gate process. The demodulation processing unit 61 performs a demodulation process on the signals having been subjected to the gate process on the basis of intrapul se modulation, and thereby generates signals having been subjected to the demodulation process. The filter processing unit 62 performs a band-pass filtering process on the signals having been subjected to the demodulation process, and thereby generates signals having been subjected to the band-pass filtering process [0014] The frequency-domain transforming unit 63 performs a frequency-domain transforming process on the signals having been subjected to the band-pass filtering process, and thereby generates frequency-domain signals. In addition, when the signal processing unit 6 does not include the filter processing unit 62, the frequency-domain transforming unit 63 receives the signals having been subjected to the demodulation process from the demodulation processing unit 61, performs a frequency-domain transform on the signals having been subjected to the demodulation process, and thereby generates frequency-domain signals.

[0015] The high accuracy achievement processing unit 64 is a transform processing unit that performs a high accuracy achieving process on the frequency-domain signals, and thereby generates signals having been subjected to the high accuracy achieving process. The high accuracy achieving process is a process in which a frequency-domain transforming process is performed on a plurality of frequency-domain signals corresponding to a plurality of reception gates, and furthermore, an inverse frequency-domain transforming process is performed on the signals having been subjected to the frequency-domain transforming process, using a larger number of points than the number of frequency-domain transform points. The signals having been subjected to the high accuracy achieving process are signals having been subjected to the above-described inverse frequency-domain transforming process.

[0016] The target candidate detecting unit 65 detects target candidates on the basis of the strength of the signals having been subjected to the high accuracy achieving process. Note that when the signal processing unit 6 does not include the high accuracy achievement processing unit 64, the target candidate detecting unit 65 detects target candidates on the basis of the strength of the frequency-domain signals inputted from the frequency-domain transforming unit 63. The target candidate distance calculating unit 66 calculates distances to the target candidates detected by the target candidate detecting unit 65 [0017] FIG. 2 is a block diagram showing a configuration of the transmitting unit 3. As shown in FIG. 2, the transmitting unit 3 includes a transmitter 30, an ntra-pulse modulator 31, a pulse modulator 32, and a local oscillator 33. The transmitter 30 outputs a transmission RF signal having been subjected to ntra-pulse modulation and generated by the intra-pulse modulator 31 to the antenna 2 through the transmission and reception switching unit 4.

[0018] The intra-pulse modulator 31 performs intra-pulse modulation on a transmission RF signal having been subjected to a pulse modulation process and generated by the pulse modulator 32, and thereby generates a transmission RF signal haying been subjected to the intra-pulse modulation. The pulse modulator 32 performs pulse modulation on a local oscillation signal inputted from the local oscillator 33, and thereby generates a transmission RF signal having been subjected to the pulse modulation. The local oscillator 33 generates a local oscillation signal and outputs the local oscillation signal to the receiving unit 5 shown in FIG. 1 and the pulse modulator 32.

[0019] FIG. 3 is a block diagram showing a configuration of the receiving unit 5. As shown in FIG. 3, the receiving unit 5 includes a receiver 50 and an AID converter 51. The receiver 50 receives, through the transmission and reception switching unit 4, a reception RF signal received by the antenna 2 The receiver 50 downconverts the reception RF signal on the basis of a local oscillation signal inputted from the local oscillator 33, and further performs signal processing on the downconverted reception RE signal and thereby generates a reception video signal The signal processing includes, for example, a band-pass filtering process, an amplification process, and a phase detection process.

[0020] The reception video signal generated by the receiver 50 is outputted to the AID converter 51. The AID converter 51 converts the reception video signal inputted from the receiver 50 into a digital signal, and outputs the converted reception video signal to the signal processing unit 6 [0021] Next, a hardware configuration that implements functions of the radar device 1 will be described.

The functions of the transmitting unit 3, the receiving unit 5, and the signal processing unit 6 in the radar device 1 are implemented by a processing circuit.

Namely, the radar device 1 includes a processing circuit for performing processes at step ST1 to step ST9 which will be described later using FIG. 5. The processing circuit may be dedicated hardware or may be a central processing unit (CPU) that executes a program stored in a memory.

[0022] FIG. 4A is a block diagram showing a hardware configuration that implements the functions of the radar device L FIG. 4B is a block diagram showing a hardware configuration that executes software that implements the functions of the radar device 1. In FIGS. 4A and 4B, an antenna 100 is the antenna 2 shown in FIG. 1, and a display 101 is the display 7 shown in FIG. I. An input and output interface 102 is an interface that relays an output of a transmission RF signal from the transmitting unit 3 shown in FIG. 1 to the antenna 100 and an output of a reflected RE signal from the antenna 100 to the receiving unit 5 shown in FIG. 1. Namely, the input and output interface 102 has a function of the transmission and reception switching unit 4 shown in FIG. I. Furthermore, the input and output interface 102 also functions as an interface that relays an output signal to the display 101.

[0023] An external storage device 103 is a storage device that stores various types of setting data and signal data which are used in signal processing performed by the signal processing unit 6 shown in FIG. 1. For example, for the external storage device 103, a volatile memory such as a synchronous dynamic random access memory (SDRAM); a hard disk drive device (HDD), or a solid state drive device (SSD) may be used. In addition, programs including an operating system (OS) may be stored in the external storage device 103. Furthermore, a memory 107 shown in FIG. 4B may be constructed in the external storage device 103. The external storage device 103 may be a storage device that is provided independently of the radar device 1 and that allows the radar device 1 to perform communication connection thereto, e.g., a storage device provided in cloud storage.

[0024] A signal path 105 is a bus through which signal data is transmitted, and in FIG. 4A, the input and output interface 102, the external storage device 103, and a processing circuit 104 are connected to each other by the signal path 105. In addition, in FIG. 4B, the input and output interface 102, the external storage device 103, a processor 106, and the memory 107 are connected to each other by the signal path 105 [0025] When the processing circuit is the processing circuit 104 which is dedicated hardware shown in FIG. 4A, the processing circuit 104 corresponds, for example, to a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof The functions of the transmitting unit 3, the receiving unit 5, and the signal processing unit 6 in the radar device 1 may be implemented by different processing circuits, or the functions may be collectively implemented by a single processing circuit.

[0026] When the processing circuit is the processor 106 shown in FIG. 4B, the functions of the transmitting unit 3, the receiving unit 5, and the signal processing unit 6 in the radar device 1 are implemented by software, firmware, or a combination of software and firmware. Note that the software or firmware is described as programs and stored in the memory 107 [0027] The processor 106 implements the functions of the transmitting unit 3, the receiving unit 5, and the signal processing unit 6 in the radar device 1 by reading and executing the programs stored in the memory 107. Namely, the radar device 1 includes the memory 107 for storing programs, the execution of which by the processor 106 results in performing processes at step ST1 to step ST9 shown in FIG. 5. The programs cause a computer to perform a procedure or a method for the transmitting unit 3, the receiving unit 5, and the signal processing unit 6. The memory 107 may be a computer readable storage medium storing therein programs for causing the computer to function as the transmitting unit 3, the receiving unit 5, and the signal processing unit 6. [0028] The memory 107 corresponds, for example, to a nonvolatile or a volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), or an electrically-EPROM (EEPROIVI); a magnetic disk, a flexible disk, an optical disc, a compact disc, a Mini Disc, or a DVD.

[0029] Some of the functions of the transmitting unit 3, the receiving unit 5, and the signal processing unit 6 may be implemented by dedicated hardware and some of the functions may be implemented by software or firmware. For example, the functions of the transmitting unit 3 and the receiving unit 5 are implemented by the processing circuit 104 which is dedicated hardware, and the functions of the signal processing unit 6 is implemented by the processor 106 reading and executing programs stored in the memory 107. As such, the processing circuit can implement the above-described functions by hardware, software, firmware, or a combination thereof.

[0030] Next, the operation will be described.

FIG. 5 is a flowchart showing operations of the radar device I according to the first embodiment, and shows a target distance measurement method according to the first embodiment. Note that intra-pulse modulation includes intra-pulse code modulation and ntra-pulse frequency modulation. The following description is made of intra-pulse code modulation as an example. In addition, FIG. 6A is a schematic diagram showing an overview of processes performed by the signal processing unit 6. FIG. GB is a diagram showing frequency-domain signals corresponding to a plurality of targets with the same velocity v. FIG. 6C is a diagram showing the waveform in a gate number direction of a frequency-domain signal corresponding to a target with the velocity v. FIG. 6D is a diagram showing the waveform in a distance direction of a signal having been subjected to an inverse frequency-domain transforming process (a signal having been subjected to a high accuracy achieving process) and corresponding to the target with the velocity v.

[0031] The transmitting unit 3 outputs a transmission RF signal having been subjected to intra-pulse code modulation to the transmission and reception switching unit 4 (step ST1). The transmission and reception switching unit 4 outputs the transmission RF signal to the antenna 2 at timing set by the transmitting unit 3. The antenna 2 radiates the transmission RF signal inputted from the transmission and reception switching unit 4 into space. A reflected wave of the transmission RF signal reflected by targets in space is received by the antenna 2. 1.3

The receiving unit 5 receives, as a reception RF signal, the signal received by the antenna 2, and generates a reception video signal on the basis of the reception RF signal (step ST2). The reception video signal generated by the receiving unit 5 is outputted to the signal processing unit 6.

[0032] The gate processing unit 60 included in the signal processing unit 6 performs a gate process in which a plurality of reception gates are set, on the reception video signal and thereby generates signals having been subjected to the gate process (step ST3).

A gate number no is a number indicating the position of a reception gate, and for example, as shown in FIG. 6A, reception gates are set in each of positions corresponding to the gate number no = 0, 1, 2, .., No-1.

[0033] Then, the demodulation processing unit 61_ performs a demodulation process on the signals having been subjected to the gate process on the basis of the intra-pulse modulation, and thereby generates signals having been subjected to the demodulation (step ST4). As shown in FIG. 6A, the demodulation processing unit 61 performs, for each reception gate, code demodulation on a reception video signal present in the reception gate.

The filter processing unit 62 performs a filtering process on the signals having been subjected to the demodulation process, and thereby generates signals having been subjected to the filtering process (step ST5). As shown in FIG. 6A, the filter processing unit 62 performs, for each reception gate, a narrow band-pass filtering process on a signal having been subjected to the demodulation process.

[0034] The frequency-domain transforming unit 63 performs a frequency-domain transforming process on the signals having been subjected to the filtering process, and thereby generates frequency-domain signals (step ST6). For example, as shown in FIG. 6A, the frequency-domain transforming unit 63 performs, for each reception gate, a fast Fourier transform (hereinafter, referred to as FFT) on a signal having been subjected to the filtering process. The frequency-domain signals each are a signal including information about Doppler frequency, i.e., velocity v, and a distance corresponding to a reception gate interval. The waveforms of signals shown in FIG. 6B are the waveforms of frequency-domain signals corresponding to each of a plurality of targets with the same velocity v. A frequency-domain signal corresponding to a target with the velocity v has, as shown in FIG. 6C, a spectrum waveform in the gate number direction, and has maximum power at a gate number no of a reception gate close to a target distance, thereby enabling ranging of the target.

[0035] The high accuracy achievement processing unit 64 performs a high accuracy achieving process on the frequency-domain signals generated by the frequency-domain transforming unit 63, and thereby generates signals having been subjected to the high accuracy achieving process (step ST7).

For example, as shown in FIG. 6A, the high accuracy achievement processing unit 64 performs an FFT process on a plurality of frequency-domain signals corresponding to each of reception gates with the gate number no = 0, 1, 2, ..., No-l. Then, the high accuracy achievement processing unit 64 performs an inverse fast Fourier transform (hereinafter, referred to as IFFT) on the signals having been subjected to the FFT process, using a larger number of points than the number of FFT points Since a sampling interval in the distance direction is subdivided by the high accuracy achieving process, the frequency-domain signals are sampled with high accuracy. The waveform of a signal having been subjected to the high accuracy achieving process has, as shown in FIG. 6D, a maximum peak near a target distance The signals having been subjected to the high accuracy achieving process and generated by the high accuracy achievement processing unit 64 are outputted to the target candidate detecting unit 65 [0036] The target candidate detecting unit 65 performs a process of detecting target candidates on the basis of the strength of the signals having been subjected to the high accuracy achieving process (step STS), Thereafter, the target candidate distance calculating unit 66 calculates distances to the target candidates detected by the target candidate detecting unit 65 (step ST9). The display 7 displays information about the distances to the target candidates inputted from the target candidate distance calculating unit 66 [0037] Next, details of operations of the transmitting unit 3 will be described.

FIG. 7 is a flowchart showing operations of the transmitting unit 3, and shows details of a process at step ST1 of FIG. 5. FIG. 8 is a diagram showing a waveform of a transmission RF signal Tx(t).

The local oscillator 33 generates a local oscillation signal Lo(t) with a constant frequency represented by the following equation (1) (step ST la). The local oscillation signal Lo(t) generated by the local oscillator 33 is outputted to the receiving unit 5 and the pulse modulator 32. In the following equation (I), t is the time, AL is the amplitude of the local oscillation signal Lo(t), and fo is the transmission frequency. Furthermore, (I)o is the initial phase of the local oscillation signal Lo(t), Tobs is the observation time, and] is the imaginary unit.

= 4:14 cxp(./(2.7r,l, [0038] The pulse modulator 32 performs a pulse modulation process that follows the following equation (2) on the local oscillation signal Lo(t) using a preset pulse repetition interval Tpn and a preset pulse width To, and thereby generates a transmission RF signal Txpts(t) having been subjected to the pulse modulation (step ST2a). The transmission RE signal Txpis(t) generated by the pulse modulator 32 is outputted to the intra-pulse modulator 31. The h is the hit number and H is the hit count.

(1) xpLi(27ef,t+R)),. < * 7 ( 2) otherwise (h 0,1, I) [0039] The hit count H is represented by the following equation (3) The floor(X) indicates an integer obtained by truncating the fractional part of a variable X. = flu f of, 7' [0040] The intra-pulse modulator 31 performs intra-pulse modulation that follows the following equation (4) on the transmission RE signal Txpis(t), using a preset pulse repetition interval Tpo, a preset pulse width To, and preset intra-pulse modulation dm.loa(t), and thereby generates a transmission RE signal Tx(t) (step ST3a). A transmission pulse a shown in FIG. 8 is a transmission pulse of the transmission RE signal Tx(t).

74t) ( 0, otherwise 13,-* 'H I) [0041] An ntra-pulse modulation code b of the transmission RE signal Tx(t) is an intra-pulse modulation code represented by a 4-bit Barker code shown in the following equation (5) Here, one bit is a sub-pulse width. The number of bits of the intrapul se modulation code b may be other than four bits. Intra-pulse modulation to be performed on the transmission RE signal Txpis(t) may be multilevel code modulation or may be intra-pulse frequency modulation. () n'

[0042] The transmitter 30 outputs the transmission RF signal Tx(t) inputted from the pulse modulator 32 to the transmission and reception switching unit 4 (step ST4a). The transmission and reception switching unit 4 outputs the transmission RF signal Tx(t) inputted from the transmitting unit 3 to the antenna 2. The antenna 2 radiates the transmission RF signal Tx(t) into the air (space).

[0043] Next, details of operations of the receiving unit 5 will be described.

FIG. 9 is a flowchart showing operations of the receiving unit 5, and shows details of a process at step ST2 of FIG. 5. FIG. 10 is a diagram showing a waveform of a reception video signal V(m').

A transmission RF signal reflected by targets in the air enters the antenna 2. The signal having entered the antenna 2 is outputted to the receiver 50, as a reception RF signal Rx(t) represented by the following equation (6) (step ST1b). In the following equation (6), nigi is the target number and No is the target count.

itv(e) x,(1) * . * th H [0044] A reception RF signal Rxiiigi(t) corresponding to a target with a target number nigi which is included in the above-described equation (6) is represented by the following equation (7). In the following equation (7), AR. Mgt is the amplitude of the reception RF signal Rxiiigi(t), Ro,ntgt is the initial target relative distance of the target with the target number nigi, and vnigi is the target relative velocity of the target with the target number mgt. The c is the speed of light. ( 7)

[0045] The receiver 50 downconverts the reception RF signal Rx(t) inputted from the antenna 2, using a local oscillation signal Lo(t) represented by the above-described equation (1), and further allows the downconverted reception RF signal Rx(t) to pass through a band-pass filter and then performs signal processing such as amplification and phase detection on the reception RF signal Rx(t) having passed through the band-pass filter (step ST2b). As a result, a reception video signal Vo(t) represented by the following equation (8) is generated The reception video signal Vo(t) generated by the receiver 50 is outputted to the AID converter 51.

s(/)/.."' (I) = th -1.) [0046] Vu, otgt(t) in the above-described equation (8) is a reception video signal corresponding to a target with a target number ntgi represented by the following equation (9) In addition, Ay litgt is the amplitude of the reception video signal VO, otgt(t) corresponding to the target with the target number ntgt. 2R,)

0, otherwise 21?, r < hT nrise

A

[0047] The AID converter 51 AID-converts the reception video signal Vu(t) inputted from the receiver 50, and thereby generates a reception video signal V(m') represented by the following equation (10) (step ST3b). The reception video signal V(m') generated by the AJD converter 51 is outputted to the signal processing unit 6. The m' is the sampling number and M' is the sampling count w.

V( ;n') r" 0,1 * (1 [0048] Vu, nio(m') included in the above-described equation (10) is a reception video signal obtained by AID-converting the reception video signal Vu, no(t) corresponding to the target with the target number mgt. The reception video signal Vo, nigi(m1) is represented by the following equation (11). In the following equation (11), At is the sampling interval of the AID-converted reception video signal Vu, nigi(m'). The reception video signal V(m') (a reception video signal c shown in FIG. 10) is a sampled signal. * (o(

[0049] When there are a plurality of targets, in the reception video signal V(m'), a plurality of reception video signals generated on the basis of a transmission RF signal reflected by each of the plurality of targets are combined together. For example, in the reception video signal c shown in FIG. 10, a reception video signal cl corresponding to a target with a target number (1) and a reception video signal c2 corresponding to a target with a target number (2) are combined together. In the reception video signal cl, an intra-pulse modulation code cl is set, and in the reception video signal c2, an intrapulse modulation code c2' is set. In FIG. 10, mod(X, Y) is the remainder after dividing a variable X by a variable Y [0050] Next, details of operations of the signal processing unit 6 will be described. FIG. 11 is a flowchart showing operations of the signal processing unit 6, and shows details of processes at step ST3 to ST9 of FIG. 5.

The signal processing unit 6 receives a reception video signal V(m') from the AJD converter 51 included in the receiving unit 5. The gate processing unit 60 included in the signal processing unit 6 performs a process on the reception video signal V(m') in accordance with the following equation (12), using a preset amount of gate slide Amu and a preset gate width, and thereby generates a signal Vu(nu, m') having been subjected to the gate process (step ST 1c). Here, NIpn is the number of samplings in a pulse repetition interval Tpri and N/Ip is the number of samplings in a pulse.

e (m'), hA1.. + niX < [0, " 0, - [00511 FIG. 12 is a diagram showing a relationship between a reception gate with a gate number no and a sampling number m'. In an example shown in FIG. 12, the gate processing unit 60 performs a gate process, with the gate width considered to be a pulse width To. Note that the position of a gate and the gate width may be arbitrarily set values. Note also that the gate processing unit 60 may set each of a plurality of reception gates to have a gate width shorter than the pulse width To. The gate processing unit 60 sets No reception gates in each of positions on the time axis corresponding to the gate number no = 0, 1, 2, No-1 at intervals of the amount of gate slide Amc.

[0052] FIG. 13A is a diagram showing the waveform of the reception video signal c. FIG. 13B is a diagram showing a waveform of a signal d having been subjected to a gate process and corresponding to a reception gate 66. FIG. 13C is a diagram showing a waveform of a signal e having been subjected to a gate process and corresponding to a reception gate G7. FIG. 13D is a diagram showing a waveform of a signal f having been subjected to a gate process and corresponding to a reception gate 68. When the gate processing unit 60 receives the reception video signal c shown in FIG. 13A, the gate processing unit 60 sets the reception gate 66, the reception gate 67, and the reception gate G8 and performs a gate process on the reception video signal c By the gate process, the signal d having been subjected to the gate process shown in FIG. 13B is generated, the signal e having been subjected to the gate process shown in FIG. 13C is generated, and the signal f having been subjected to the gate process shown in FIG. 13D is generated.

[0053] In addition, the signal having been subjected to the gate process can be represented by VG(nc, m'). The signal d having been subjected to the gate process is a signal VG(6, m') having been subjected to the gate process, the signal e having been subjected to the gate process is a signal VG(7, m') having been subjected to the gate process, and the signal f having been subjected to the gate process is a signal VG(8, m') having been subjected to the gate process. When there are a plurality of targets, in the signal VG(nG, m') having been subjected to the gate process, a plurality of signals having been subjected to the gate process and corresponding to each of plurality of targets are combined together.

[0054] For example, when the target with the target number (1) and the target with the target number (2) are present, in the signal d having been subjected to the gate process, as shown in FIG. 13B, a signal dl having been subjected to the gate process and corresponding to the target with the target number (1) and a signal d2 having been subjected to the gate process and corresponding to the target with the target number (2) are combined together. In addition, the signal dl having been subjected to the gate process includes an intra-pulse modulation code dl' and the signal d2 having been subjected to the gate process includes an intra-pulse modulation code d2'.

[0055] In the signal e having been subjected to the gate process, as shown in FIG. 13C, a signal el having been subjected to the gate process and corresponding to the target with the target number (1) and a signal e2 having been subjected to the gate process and corresponding to the target with the target number (2) are combined together. In addition, the signal el having been subjected to the gate process includes an intra-pulse modulation code el ' and the signal e2 having been subjected to the gate process includes an intra-pulse modulation code e2'.

[0056] In the signal f having been subjected to the gate process, as shown in FIG. 13D, a signal fl having been subjected to the gate process and corresponding to the target with the target number (1) and a signal f2 having been subjected to the gate process and corresponding to the target with the target number (2) are combined together. In addition, the signal fl having been subjected to the gate process includes an intra-pulse modulation code fl' and the signal 12 having been subjected to the gate process includes an intra-pulse modulation code f2'.

[0057] In addition, the reception gate 07 is a gate slid by the amount of gate slide Amu from the reception gate 06, and the reception gate 08 is a gate slid by the amount of gate slide Amu from the reception gate 07. By the gate processing unit 60 performing a gate process, there is no influence of noise other than in a reception gate, and thus, the signal-to-noise ratio (hereinafter, referred to as SNR) of frequency-domain signals generated by the frequency-domain transforming unit 63 improves and the radar device 1 with improved target detection performance can be obtained.

[0058] Now, the description goes back to FIG. 11.

Subsequently, the demodulation processing unit 61 performs a demodulation process that follows the following equation (13) on the signal Vu(nu, m') having been subjected to the gate process and generated by the gate processing unit 60, on the basis of intra-pulse demodulation li(nu, m'), and thereby generates a signal VG, D(nu, m') having been subjected to the demodulation process (step ST2c).

D

fir = 9,1,* * * "V 1) ( 1 3) (iril = 0,1, * 41 -1) [0059] The demodulation processing unit 61 calculates intra-pulse demodulation D(nG, m') in accordance with the following equation (14) to demodulate an intra-pulse modulation code, and uses the intra-pulse demodulation D4,(nG, m') in a demodulation process other n!"&n,. JIM rkArn" 1 rio.(n",a0=2 iicxx.11(- ne (n" 0,1,- -I) [0060] FIG. 14A is a diagram showing the waveform of the reception video signal c. FIG. 14B is a diagram showing a waveform of a signal g having been subjected to a demodulation process and corresponding to the reception gate G6. FIG. 14C is a diagram showing a waveform of a signal h having been subjected to a demodulation process and corresponding to the reception gate G7. FIG. 14D is a diagram showing a waveform of a signal i having been subjected to a demodulation process and corresponding to the reception gate G8. The demodulation processing unit 61 performs a demodulation process on the signal d having been subjected to the gate process shown in FIG. 13B, and thereby generates the signal g having been subjected to the demodulation process shown in FIG. 14B. In addition, the demodulation processing unit 61 performs a demodulation process on the signal e having been subjected to the gate process shown in FIG. 13C, and thereby generates the signal h having been subjected to the demodulation process shown in FIG. 14C. The demodulation processing unit 61 performs a demodulation process on the signal f having been subjected to the gate process shown in FIG. 13D, and thereby generates the signal i having been subjected to the demodulation process shown in FIG. 14D. [0061] In addition, the signal having been subjected to the demodulation process can be represented by VG, u(nG, m'). The signal g having been subjected to the demodulation process is a signal Vu, D(6, m') haying been subjected to the demodulation process, the signal h having been subjected to the demodulation process is a signal VG. D(7, m') having been subjected to the demodulation process, and the signal i having been subjected to the demodulation process is a signal VG, 0(8, m') haying been subjected to the demodulation process. A signal Vo, mg( b(no, m') having been subjected to a demodulation process and generated on the basis of a reception RF signal corresponding to a target with a target number nigt can be represented by the following equation (15). In the following equation (15), Vo ntgt(na, m') is a signal haying been subjected to the gate process and generated on the basis of the reception RF signal corresponding to the target with the target number no, and 4/Mod n(nG, m') is a code haying been subjected to the demodulation process [0062] As shown in FIG. 14B, in a signal gl haying been subjected to the demodulation process and corresponding to a reception RF signal for the target with the target number (1) present in the reception gate G6, the intra-pulse modulation code dl' and an intra-pulse demodulation code match each other, and thus, the signal gl has no modulation gl' The signal gl having been subjected to the demodulation process is Al (in1-0e,1,( -)1) (hAl. i flyAflj: fin" < hiti = ---I) taf =0,1,**. "II' -1) coherently integrated when transformed into a frequency-domain signal by the frequency-domain transforming unit 63.

On the other hand, a signal g2 having been subjected to the demodulation process and corresponding to a reception RF signal for the target with the target number (2) present in the reception gate G6, the intra-pulse modulation code d2' and an intrapulse demodulation code do not match each other, and thus, a modulation code g2' remains. The signal g2 having been subjected to the demodulation process in which the modulation code g2' remains is not coherently integrated when transformed into a frequency-domain signal. In the reception gate G6, the signal g I having been subjected to the demodulation process is coherently integrated and the target with the target number (1) can be separated.

[0063] As shown in FIG. 14C, in a signal hl having been subjected to the demodulation process and corresponding to the reception RF signal for the target with the target number (1) present in the reception gate G7, the intra-pulse modulation code hl' and an intra-pulse demodulation code do not match each other, and thus, a modulation code hi' remains. In a signal h2 having been subjected to the demodulation process and corresponding to the reception RF signal for the target with the target number (2) present in the reception gate 137, the intra-pulse modulation code h2' and an intra-pulse demodulation code do not match each other, and thus, a modulation code h2' remains. As a result, the signals hl and h2 having been subjected to the demodulation process are not coherently integrated when transformed into frequency-domain signals.

[0064] As shown in FIG. 14D, in a signal il having been subjected to the demodulation process and corresponding to the reception RF signal for the target with the target number (1) present in the reception gate G8, the intra-pulse modulation code i t ' arid an intra-pulse demodulation code do not match each other, and thus, a modulation code il' remains. On the other hand, in a signal i2 having been subjected to the demodulation process and corresponding to the reception RF signal for the target with the target number (2) present in the reception gate G8, the intra-pulse modulation code IT and an intra-pulse demodulation code match each other, and thus, the signal i2 has no modulation i2'. The signal 12 having been subjected to the demodulation process is coherently integrated when transformed into a frequency-domain signal by the frequency-domain transforming unit 63. In the reception gate G8, the signal 12 having been subjected to the demodulation process is coherently integrated and the target with the target number (2) can be separated [0065] As such, a signal having been subjected to the demodulation process and having modulation remaining therein is not coherently integrated, but a signal having been subjected to the demodulation process and having no modulation is coherently integrated, and thus, the target separation performance of the radar device 1 improves. The radar device 1 performs intra-pulse code modulation on a transmission signal, by which even when a plurality of targets are present in a single reception gate, the targets can be separated at a resolution less than or equal to the amount of gate slide Amu. The signal VG, u(nG, m') having been subjected to the demodulation process and generated by the demodulation processing unit 61 is outputted to the filter processing unit 62

[0066] Now, the description goes back to FIG. 11

Subsequently, the filter processing unit 62 performs a narrow band-pass filtering process that allows signals in a band around the center of spectrum of the frequency domain to pass through, on the signal Vau(no, m') having been subjected to the demodulation process, and thereby generates a signal having been subjected to the narrow band-pass filtering process (step ST3c). A signal VG, D, f(no, m) having been subjected to the narrow band-pass filtering process is represented by the following equation (16). In the following equation (16), m is the sampling number of the signal having been subjected to the narrow band-pass filtering process, and Nil is the sampling count of the signal having been subjected to the narrow band-pass filtering process.

in) Iirr: D * = 0,1,, * , -1) (ot XI -0 [0067] In the above-described equation (16), VG, D. f. ntgt(nG, IT) is a signal having been subjected to the narrow band-pass filtering process and represented by the following equation (17), and corresponds to a target with a target number nigi present in a reception gate with a gate number nG. In addition, AG. nIgt 1S the amplitude of the signal VG, D, Ingt(nG, m) having been subjected to the narrow band-pass filtering process. By performing the narrow band-pass filtering process, sampling with coarse sampling intervals can be performed without impairing information on the center of spectrum of the frequency domain of a signal having been subjected to the demodulation process. Since the number of signal points decreases and the amount of computation in signal processing decreases, the radar device 1 with small hardware size can be implemented.

[0068] The signal VG(nG, m') having been subjected to the gate process achieves time =0,1,-- -I) =0,1,,* * "if -1) xPicil,/b&v.,: kin £1/4All synchronization between the reception gates, and the signal Vci, o(no, m') having been subjected to the demodulation process also achieves time synchronization between the reception gates Hence, the filter processing unit 62 starts a narrow band-pass filtering process at the same time (the same sampling number) regardless of the position of each of the plurality of reception gates. As a result, the signal VG, D, ((no, m) having been subjected to the narrow band-pass filtering process achieves time synchronization between the reception gates. The signal VG, D. ((no, m) having been subjected to the narrow band-pass filtering process is outputted to the frequency-domain transforming unit 63. When the signal processing unit 6 does not include the filter processing unit 62, the signals having been subjected to the demodulation process and generated by the demodulation processing unit 61 are outputted to the frequency-domain transforming unit 63.

[0069] Then, the frequency-domain transforming unit 63 performs a frequency-domain transforming process that follows the following equation (18) on the signal VG, o, ((no, m) having been subjected to the narrow band-pass filtering process and inputted from the filter processing unit 62, and thereby generates a frequency-domain signal fd(nG, k) (step ST4c). Note, however, that in the following equation (18), k is the sampling number in the frequency domain and Mm is the number of frequency-domain transform points. Although a discrete Fourier transform shown in the following equation (18) is used in the frequency-domain transforming process, the frequency-domain transforming process may be performed using an FFT or a chirp-z transform.

(n" )exp [0070] In addition, when the signal processing unit 6 does not include the filter processing unit 62, the frequency-domain transforming unit 63 likewise performs a frequency-domain transforming process that follows the above-described equation (18) on the signals having been subjected to the demodulation process and inputted from the demodulation processing unit 61, and thereby generates a frequency-domain signal fd(no, k). The frequency-domain signal L(nG, k) generated by the frequency-domain transforming unit 63 is outputted to the high accuracy achievement processing unit 64. [0071] As shown in FIG. 6B, the frequency-domain signal fd(no, k) is a signal including information on velocity v and a distance between gate intervals. In addition, as shown in FIG. 6C, a frequency-domain signal corresponding to a target with the velocity v has a waveform in the gate number direction. The waveform exhibits maximum power at a reception gate close to a target distance, and ranging of the target using the signal in the reception gate is possible. When a filtering process is performed on a signal having been subjected to a demodulation process, the signal loses its pulse shape and is converted into a sine wave, but by transforming the signal into a frequency-domain signal, the signal whose power changes between reception gates is obtained. As a result, targets close to each other at a distance shorter than the pulse width To can be separated from each other.

[0072] FIG. 15A is a diagram showing the waveforms of the measured values of frequency-domain signals corresponding to a plurality of targets with the same velocity v present in reception gates for a case in which a transmission RF signal has not been subjected to intra-pulse modulation. In FIG. 15A, waveforms indicated by solid lines are the waveforms of the measured values of frequency-domain signals at each of gate start bins mo(no-1), mo(no), mo(no+1), and mo(no+2) of the gate number no. In the frequency-domain signals, a frequency-domain signal corresponding to the target with the target number (1) and a frequency-domain signal corresponding to the target with the target number (2) are combined together [0073] FIG. 15B is a diagram showing the waveforms of frequency-domain signals for each of the targets with the same velocity v present in reception gates for a case in which a transmission RF signal has not been subjected to intra-pulse modulation. In FIG. 15B, waveforms indicated by dashed lines are the waveforms of frequency-domain signals corresponding to the target with the target number (1), and waveforms indicated by dash-dotted lines are the waveforms of frequency-domain signals corresponding to the target with the target number (2). The waveforms of the frequency-domain signals corresponding to the target with the target number (1) have maximum power at a distance corresponding to the gate start bin mo(nG), and also have high power at distances corresponding to other gate start bins. The waveforms of the frequency-domain signals corresponding to the target with the target number (2) have maximum power at a distance corresponding to the gate start bin mct(nG+1), and also have high power at distances corresponding to other gate start bins.

[0074] FIG. 15C is a diagram showing the waveforms of the measured values of frequency-domain signals corresponding to a plurality of targets with the same velocity v present in reception gates for a case in which a transmission RF signal has been subjected to intra-pulse modulation. The waveforms are the waveforms of the measured values of frequency-domain signals at each of gate start bins mG(nG-1), mG(nG), mG(nG+1), and mG(nG+2) of the gate number nG. In the frequency-domain signals, a frequency-domain signal corresponding to the target with the target number (1) and a frequency-domain signal corresponding to the target with the target number (2) are combined together.

[0075] FIG. 15D is a diagram showing the waveforms of frequency-domain signals for each of the targets with the same velocity v present in reception gates for a case in which a transmission RF signal has been subjected to intra-pulse modulation. In FIG. 15D, waveforms indicated by dashed lines are the waveforms of frequency-domain signals corresponding to the target with the target number (1), and waveforms indicated by dash-dotted lines are the waveforms of frequency-domain signals corresponding to the target with the target number (2). The waveforms of the frequency-domain signals corresponding to the target with the target number (1) have maximum power at a distance corresponding to the gate start bin mG(nG), and have relatively low power at distances corresponding to other gate start bins. The waveforms of the frequency-domain signals corresponding to the target with the target number (2) have maximum power at a distance corresponding to the gate start bin mo(nG+1), and have relatively low power at distances corresponding to other gate start bins.

[0076] FIG. 16A is a diagram showing the waveform of the reception video signal c. FIG. 16B is a diagram showing the waveforms in the gate number direction of the measured values of frequency-domain signals for each of targets with the same velocity v present in reception gates for a case in which a transmission signal has not been subjected to intra-pulse modulation. In FIG. 16B, a waveform j 1 is a waveform of a frequency-domain signal generated on the basis of the reception video signal cl obtained by receiving a transmission RF signal having not been subjected to ntra-pulse modulation. A waveform j2 is a waveform of a frequency-domain signal generated on the basis of the reception video signal c2 obtained by receiving a transmission RF signal having not been subjected to intra-pulse modulation. The waveform jl of the frequency-domain signal corresponding to the target with the target number (1) has maximum power at a reception gate with the gate number nu = 6, and also has high power at adjacent reception gates. Likewise, the waveform j2 of the frequency-domain signal corresponding to the target with the target number (2) has maximum power at a reception gate with the gate number nu = 8, and also has high power at adjacent reception gates.

[0077] FIG. 16C is a diagram showing the waveforms in the gate number direction of the measured values of frequency-domain signals for each of targets with the same velocity v present in reception gates for a case in which a transmission RF signal has been subjected to ntra-pulse modulation. In FIG. 16C, a waveform la is a waveform of a frequency-domain signal generated on the basis of the reception video signal cl obtained by receiving a transmission RF signal having been subjected to intra-pulse modulation. A waveform k2 is a waveform of a frequency-domain signal generated on the basis of the reception video signal c2 obtained by receiving a transmission RF signal having been subjected to intra-pul se modulation. The waveform k 1 of the frequency-domain signal corresponding to the target with the target number (1) has maximum power at a reception gate with the gate number nu = 6, and has low power at adjacent reception gates. Likewise, the waveform k2 of the frequency-domain signal corresponding to the target with the target number (2) has maximum power at a reception gate with the gate number 66 = 8, and has low power at adjacent reception gates [0078] When a transmission signal has not been subjected to intra-pulse modulation, if there are a plurality of targets with the same velocity, then as shown in FIGS. 15A, 15B, and 1 6B, the distance resolution of the radar device decreases, thereby degrading target ranging performance On the other hand, when a transmission signal has been subjected to intra-pulse modulation, by performing a gate process, a demodulation process, a filtering process, and a frequency-domain transforming process on a reception signal, as shown in FIGS. 15C, 15D, and 16C, the distance resolution of the radar device improves, thereby improving target ranging performance.

[0079] A relationship in the following expression (19) holds true between the distance resolution ATO of the radar device at a time when a transmission signal has not been subjected to intra-pulse modulation and the distance resolution Am of the radar device at a time when a transmission signal has been subjected to intra-pulse modulation. As shown in the following expression (19), the distance resolution Am is higher resolution than the distance resolution ATO. A relationship in the following expression (20) holds true between the ranging accuracy ta Accuracy of the radar device at a time when a transmission signal has not been subjected to intra-pulse modulation and the ranging accuracy Tb. accuracy of the radar device at a time when a transmission signal has been subjected to intra-pulse modulation. As shown in the following expression (20), the ranging accuracy th, accuracy is higher accuracy than the ranging accuracy to, accuracy. In the following expression (20), snr is the signal-to-noise ratio.

( 1 9) ) ) [0080] Furthermore, a frequency-domain signal fa, gtgt(nG, k) corresponding to a target with a target number ntgt in a reception gate with a gate number nc is represented by the following equation (21). When a relationship shown in the following equation (22) holds true in the following equation (21), the frequency-domain signal fa, mgt(no, k) exhibits a maximum amplitude value. Note that in the following equation (22), kpeak is the sampling number k of the frequency-domain signal fa, gtgt(nG, k) at which the maximum amplitude value is exhibited.

2v, Ar kr..# xp( ( 1) [0081] As shown in FIG. 13B, passage of the reception gate G6 with the gate number no = 6 starts at the sampling number m' = 6. In addition, as shown in FIG. 13D, passage of the reception gate G8 with the gate number no = 8 starts at the sampling number m' = 8. In a gate process performed by the gate processing unit 60, the passage start times of a plurality of reception gates differ from each other, but a signal Vo(no, m') having been subjected to a gate process and a signal Vo(no, m) having been subjected to a narrow band-pass filtering process achieve time synchronization between the reception gates.

[0082] In addition, as shown in the above-described equation (18), the frequency-domain transforming unit 63 starts a frequency-domain transforming process at the same time (the same sampling number) regardless of the position of each of the plurality of reception gates. The demodulation processing unit 61 performs a demodulation process on a signal having been subjected to a gate process, and thereby demodulates an intra-pulse modulation code. Hence, the radar device 1 can perform control not to change the sampling number kpeak at which a frequency-domain signal corresponding to each of a plurality of targets exhibits its maximum amplitude value. [0083] Now, the description goes back to FIG. 11.

Subsequently, the high accuracy achievement processing unit 64 performs a high accuracy achieving process on the frequency-domain signal fa(no, k) inputted from the frequency-domain transforming unit 63, and thereby generates a signal having been subjected to the high accuracy achieving process (step ST5c). For example, the high accuracy achievement processing unit 64 performs a Fourier transform process that follows the following equation (23) on a frequency-domain signal fa(no, k) corresponding to each of the plurality of reception gates, and thereby generates a frequency-domain signal fa, G(q, k). Note, however, that in the following equation (23), NG fil is the number of Fourier transform points (the number of frequency-domain transform points between gates) and q is the sampling number of the signal having been subjected to the Fourier transform process ( 2 a) [0084] The high accuracy achievement processing unit 64 performs an inverse Fourier transform process that follows the following equation (24) on the frequency-domain signal fa G(q, k), using a larger number of transform points NG. LER than the number of Fourier transform points NG, fft as shown in the following expression (25), and thereby generates a signal f' d, G(qa-ft, k) having been subjected to the high accuracy achieving process. In the following equation (24) and the following expression (25), NG, im is the number of inverse Fourier transform points (the number of inverse frequency-domain transform points) and corresponds to the number of samplings in the distance direction of the signal having been subjected to the high accuracy achieving process. The gall is the sampling number in the distance direction of the signal having been subjected to the high accuracy achieving process.

* ( 2 4) * * * ( 2 5) [0085] For example, when the number of inverse Fourier transform points NG, im is NG, multi times the number of Fourier transform points NG, rn, a distance sampling interval airi of the signal f' d, k) having been subjected to the high accuracy achieving process is 1/No, sawn of Amu as shown in the following equation (26) As such, the distance sampling interval is subdivided into Am. ifft from AmG 7 Am, ( 2 6) [0086] FIG. 17A is a diagram showing the waveforms of frequency-domain signals corresponding to each of targets with the same velocity present in reception gates. In FIG. 17A, a reception gate with a gate number no has a gate width that is 1/4 of the pulse width To. A waveform Li indicated by a dotted line is a waveform of a frequency-domain signal corresponding to the target with the target number (I), and a waveform L2 indicated by a dash-dotted line is a waveform of a frequency-domain signal corresponding to the target with the target number (2).

[0087] The distance to the target with the target number (1) is a distance corresponding to the center of a sub-pulse corresponding to the gate number no = 6, and the distance to the target with the target number (2) is a distance corresponding to the center of a sub-pulse corresponding to the gate number no = 7. When the target with the target number (1) and the target with the target number (2) are close to each other at a distance shorter than the pulse width To, a filter shape loss occurs in the frequency-domain signals corresponding to each of targets. As a result, as shown in FIG. 17A, an integration loss occurs in the frequency-domain signals, and it becomes difficult to perform detection and separation of the targets.

[0088] FIG. 17B is a diagram showing the waveforms of signals having been subjected to a high accuracy achieving process and corresponding to each of targets with the same velocity present in reception gates. In FIG. 17B, a distance sampling interval corresponding to the gate number no is subdivided into Am. lift from AmG. A waveform ml indicated by a solid line is a waveform of a signal having been subjected to a high accuracy achieving process and corresponding to the target with the target number (1), and a waveform m2 indicated by a dash-dotted line is a waveform of a signal having been subjected to a high accuracy achieving process and corresponding to the target with the target number (2). The distance to the target with the target number (1) is a distance corresponding to the center of a sub-pulse corresponding to the gate number no = 6, and the distance to the target with the target number (2) is a distance corresponding to the center of a sub-pulse corresponding to the gate number no = 7. [0089] As shown in FIG. 17B, by performing a high accuracy achieving process on the frequency-domain signal corresponding to the target with the target number (1) and the frequency-domain signal corresponding to the target with the target number (2), the distance sampling interval is subdivided into Am. 'M. As a result, even if the target with the target number (1) and the target with the target number (2) come close to each other at a distance shorter than the pulse width To, an integration loss does not occur in the frequency-domain signals, thereby enabling detection and separation of the targets. [0090] The signal f'd G(qiret, k) having been subjected to the high accuracy achieving process and generated by the high accuracy achievement processing unit 64 is outputted to the target candidate detecting unit 65 Note that when the signal processing unit 6 does not include the high accuracy achievement processing unit 64, the target candidate detecting unit 65 receives the frequency-domain signal fd(no, k) from the frequency-domain transforming unit 63.

[0091] The target candidate detecting unit 65 detects target candidates on the basis of the strength of the signal Ca u(qait, k) having been subjected to the high accuracy achieving process (step ST6c). For example, the target candidate detecting unit 65 detects target candidates using a cell average constant false alarm rate (CA-CFAR) process. In the CA-CFAR process, target candidates are detected in such a manner that a false alarm rate Pia has a constant specified value. Hence, the target candidate detecting unit 65 can control erroneous detection of target candidates, enabling detection of target candidates on the basis of the strength of signals having been subjected to a high accuracy achieving process or frequency-domain signals, without detecting noise as much as possible. In addition, the target candidate detecting unit 65 detects target candidates on the basis of signal strength and thus can control the strength of signals corresponding to the target candidates, by which the accuracy of distance based on the strength of the signals is obtained.

[0092] Thereafter, the target candidate detecting unit 65 outputs to the target candidate distance calculating unit 66 the signal fa. c(qtra, k) having been subjected to the high accuracy achieving process and inputted from the high accuracy achievement processing unit 64, and the sampling number qiiri aigt in the distance direction and sampling number kntgt in a velocity direction of a signal having been subjected to the high accuracy achieving process and corresponding to a target candidate with a target number nita detected in the CA-CFAR process. By the sampling number gait, ntgt in the distance direction arid sampling number katLa in the velocity direction of the signal having been subjected to the high accuracy achieving process, the value in the distance direction and the value in the velocity direction of the signal obtained by a series of processes shown in FIG. 6A are identified (see the relationship between distance and velocity shown in FIG. 6A).

[0093] When the signal processing unit 6 does not include the high accuracy achievement processing unit 64, the target candidate detecting unit 65 detects target candidates on the basis of the strength of the frequency-domain signal fd(no, k) generated by the frequency-domain transforming unit 63. The target candidate detecting unit 65 outputs to the target candidate distance calculating unit 66 the frequency-domain signal fd(nG, k) inputted from the frequency-domain transforming unit 63, and the gate number no, no and sampling number kno in the velocity direction of a frequency-domain signal corresponding to a target candidate with a target number met detected in the CA-CFAR process.

[0094] The target candidate distance calculating unit 66 calculates a distance R' O. ntgt to the target candidate with the target number ntut detected by the target candidate detecting unit 65, in accordance with the following equation (27) (step ST7c). The distance Wo, id(d calculated by the target candidate distance calculating unit 66 is outputted to the display 7. The display 7 displays the distance R'o. Mgt to the target candidate with the target number nig( that is inputted from the target candidate distance calculating unit 66 on a screen, as target information.

* ( f1 7) [0095] When the signal processing unit 6 does not include the high accuracy achievement processing unit 64, the target candidate distance calculating unit 66 calculates a distance R'o.nt(rt to the target candidate with the target number ntut detected by the target candidate detecting unit 65, in accordance with the following equation (28). The distance Wu. mgt calculated by the target candidate distance calculating unit 66 is outputted to the display 7. The display 7 displays the distance Wu, mg" to the target candidate with the target number nijii that is inputted from the target candidate distance calculating unit 66 on a screen, as target information.

( 2 H* ) [0096] When the velocity of a target candidate is displayed, the target candidate distance calculating unit 66 may calculate the velocity 1/ ntgt of the target candidate with the target number mgt in accordance with the following equation (29). The Aintgt calculated by the target candidate distance calculating unit 66 is outputted to the display 7 The display 7 displays the velocity v'lligi of the target candidate with the target number nig( inputted from the target candidate distance calculating unit 66 on a screen, as a target candidate.

[0097] As described above, the radar device 1 according to the first embodiment radiates a transmission RF signal having been subjected to intra-pulse modulation into space, performs a gate process in which a plurality of reception gates are set, on a reception video signal generated on the basis of the transmission RF signal reflected by targets in space, performs a demodulation process on signals having been subjected to the gate process, performs a frequency-domain transform on signals having been subjected to the demodulation process, detects target candidates on the basis of the strength of frequency-domain signals, and calculates distances to the target candidates. By this configuration, even when there are a plurality of targets in a reception gate, target distances can be accurately measured. By performing a gate process in which a plurality of reception gates are set, the influence of noise between the reception gates is suppressed, thereby improving the target detection performance of the radar device 1. [0098] The radar device 1 according to the first embodiment includes the high accuracy achievement processing unit 64 that performs a high accuracy achieving process on frequency-domain signals generated by the frequency-domain transforming unit 63, and thereby generates signals having been subjected to the high accuracy achieving process. The target candidate detecting unit 65 detects target candidates on the basis of the strength of the signals having been subjected to the high accuracy achieving process. Since a filter shape loss is reduced by the high accuracy achieving process, the target detection performance of the radar device 1 improves and target separation performance also improves.

[0099] The radar device 1 according to the first embodiment includes the filter processing unit 62 that performs a band-pass filtering process on the signals having been subjected to the demodulation process, and thereby generates signals having been subjected to the band-pass filtering process. The frequency-domain transforming unit 63 performs a frequency-domain transform on the signals having been subjected to the band-pass filtering process, and thereby generates frequency-domain signals. By performing the band-pass filtering process, sampling with coarse sampling intervals can be performed. As a result, the number of signal points decreases and the amount of computation in signal processing decreases, and thus, the radar device 1 with small hardware size can be implemented.

[0100] Note that the present invention is not limited to the above-described embodiment, and modifications to any component of the embodiment, or omissions of any component in the embodiment are possible within the scope of the present 4:3 invention

INDUSTRIAL APPLICABILITY

[0101] Radar devices according to the present invention can accurately measure target distances even when there are a plurality of targets in a reception gate, and thus, can be used as various types of radar devices.

REFERENCE SIGNS LIST

[0102] 1: radar device, 2, 100: antenna, 3: transmitting unit, 4: transmission and reception switching unit, 5: receiving unit, 6: signal processing unit, 7, 101. display, 30: transmitter, 31: ntra-pulse modulator, 32: pulse modulator, 33: local oscillator, 50: receiver,51: AID converter, 60 ate processing unit, 61: demodulation processing unit, 62: filter processing unit, 63: frequency-domain transforming unit, 64: high accuracy achievement processing unit, 65: target candidate detecting unit, 66: target candidate distance calculating unit, 102: input and output interface, 103: external storage device, 104: processing circuit, 105. signal path, 106: processor, 107: memory

Claims

CLAIMSA radar device comprising: a transmitting unit for outputting a transmission signal having been subjected to intra-pulse modulation; a receiving unit for generating a reception signal on a basis of the transmission signal reflected by a target in space; a gate processing unit for performing a gate process in which a plurality of reception gates are set, on the reception signal to generate signals having been subjected to the gate process; a demodulation processing unit for performing a demodulation process on the signals having been subjected to the gate process on a basis of the intra-pulse modulation, to generate signals having been subjected to the demodulation process; a frequency-domain transforming unit for performing a frequency-domain transforming process on the signals having been subjected to the demodulation process, to generate frequency-domain signals; a target candidate detecting unit for detecting a target candidate on a basis of strength of the frequency-domain signals; and a target candidate distance calculating unit for calculating a distance to the target candidate detected by the target candidate detecting unit.
The radar device according to claim 1, wherein the transmitting unit generates a transmission signal having been subjected to intra-pulse code modulation.
3. The radar device according to claim 1, wherein the transmitting unit generates a transmission signal having been subjected to intra-pulse frequency modulation.
The radar device according to claim 1, wherein the gate processing unit sets each of the plurality of reception gates at a shorter interval than a pulse width.
5. The radar device according to claim 1, wherein the frequency-domain transforming unit starts the frequency-domain transforming process at a same time in each of the reception gates set by the gate processing unit.
The radar device according to claim 1, comprising a high accuracy achievement processing unit for performing a frequency-domain transforming process on the plurality of frequency-domain signals corresponding to the plurality of reception gates, and performing an inverse frequency-domain transforming process on the signals having been subjected to the frequency-domain transforming process, using a larger number of transform points than a number of frequency-domain transform points, to generate signals having been subjected to the inverse frequency-domain transforming process, wherein the target candidate detecting unit detects a target candidate on a basis of strength of the signals having been subjected to the inverse frequency-domain transforming process.
7. The radar device according to claim 1, comprising a filter processing unit for performing a band-pass filtering process on the signals having been subjected to the demodulation process, to generate signals having been subjected to the band-pass filtering process, wherein the frequency-domain transforming unit performs a frequency-domain transform on the signals having been subjected to the band-pass filtering process, to generate frequency-domain signals.
8. The radar device according to claim 7, wherein the filter processing unit starts the band-pass filtering process at a same time in each of the reception gates set by the gate processing unit.
A target distance measurement method comprising the steps of outputting, by a transmitting unit, a transmission signal having been subjected to intra-pulse modulation; generating, by a receiving unit, a reception signal on a basis of the transmission signal reflected by a target in space; performing, by a gate processing unit, a gate process in which a plurality of reception gates are set, on the reception signal to generate signals having been subjected to the gate process; performing, by a demodulation processing unit, a demodulation process on the signals having been subjected to the gate process on a basis of the intra-pulse modulation, to generate signals having been subjected to the demodulation, performing, by a frequency-domain transforming unit, a frequency-domain transform on the signals having been subjected to the demodulation, to generate frequency-domain signals; detecting, by a target candidate detecting unit, a target candidate on a basis of strength of the frequency-domain signals; and calculating, by a target candidate distance calculating unit, a distance to the target candidate detected by the target candidate detecting unit.
10. The target distance measurement method according to claim 9, comprising a step of performing, by a high accuracy achievement processing unit, a frequency-domain transforming process on the plurality of frequency-domain signals corresponding to the plurality of reception gates, and performing an inverse frequency-domain transforming process on the signals haying been subjected to the frequency-domain transforming process, using a larger number of transform points than a number of frequency-domain transform points, to generate signals having been subjected to the inverse frequency-domain transforming process, wherein the target candidate detecting unit detects a target candidate on a basis of strength of the signals haying been subjected to the inverse frequency-domain transforming process.
11. The target distance measurement method according to claim 9 or 10, comprising a step of performing, by a filter processing unit, a band-pass filtering process on the signals having been subjected to the demodulation, to generate signals having been subjected to the band-pass filtering process, wherein the frequency-domain transforming unit performs a frequency-domain transform on the signals having been subjected to the band-pass filtering process, to generate frequency-domain signals.