GB2552599A

GB2552599A - Radar device

Info

Publication number: GB2552599A
Application number: GB1712766.3A
Authority: GB
Inventors: Kageme Satoshi; Suzuki Nobuhiro
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2015-04-10
Filing date: 2015-04-10
Publication date: 2018-01-31
Anticipated expiration: 2035-04-10
Also published as: GB2552599C; JPWO2016163027A1; JP6289744B2; WO2016163027A1; GB2552599B; GB2552599C2; GB201712766D0

Abstract

A radar device is provided with a pulse modulator (203) for generating a pulse signal, a transmitter (101) for generating a transmission signal from the pulse signal, an antenna element (102) for emitting the transmission signal into the air, a plurality of antenna elements (204) for receiving reception signals reflected by a target, phase shifters (205) for converting the received reception signals into signals having mutually different wavelengths, an adder (206) for adding the converted reception signals and generating a reception video signal, an A/D converter (208) for carrying out A/D conversion on the added reception video signal, a frequency range conversion unit (301) for converting the A/D converted reception video signal into frequency ranges, a target candidate detection unit (302) for detecting a target candidate from the signal power of the converted reception video signal, and a target candidate direction calculation unit (303) for calculating the direction of the target candidate from the detection results.

Description

(54) Title of the Invention: Radar device Abstract Title: Radar device (57) A radar device is provided with a pulse modulator (203) for generating a pulse signal, a transmitter (101) for generating a transmission signal from the pulse signal, an antenna element (102) for emitting the transmission signal into the air, a plurality of antenna elements (204) for receiving reception signals reflected by a target, phase shifters (205) for converting the received reception signals into signals having mutually different wavelengths, an adder (206) for adding the converted reception signals and generating a reception video signal, an A/D converter (208) for carrying out A/D conversion on the added reception video signal, a frequency range conversion unit (301) for converting the A/D converted reception video signal into frequency ranges, a target candidate detection unit (302) for detecting a target candidate from the signal power of the converted reception video signal, and a target candidate direction calculation unit (303) for calculating the direction of the target candidate from the detection results.

Transmission unit

Reception unit

Signal processor

Display

101 Transmitter

201 Local oscillator

202 Para meter ca leu lator

203 Pulse modulator

208 A/D converter

301 Frequency range conversion unit

302 Target candidate detection unit

303 Target candidate direction calculation unit

304 Target candidate relative speed calculation unit

305 Target candidate relative distance calculation unit

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DESCRIPTION

TITLE OF INVENTION

RADAR APPARATUS

TECHNICAL FIELD [0001]

The present invention relates to a radar apparatus that searches for a target which is an observation object.

BACKGROUND ART [0002]

Conventionally, a radar apparatus that forms a plurality of antenna patterns by performing digital signal processing and carries out signal processing and that uses DBF (Digital Beam Forming) is known (for example, refer to Nonpatent Literature 1). In this radar apparatus, A/D converters are disposed respectively for antenna elements. As a result, a received signal received by each antenna element can be inputted to a digital signal processing unit, and the digital signal processing unit can form a plurality of antenna patterns. Therefore, the radar apparatus can carry out signal processing at a time of orienting an antenna pattern toward each of a plurality of directions, and detect a target in each of the directions .

CITATION LIST

Non Patent Literature [0003]

Non Patent Literature 1: Institute of Electronics, Information and Communication Engineers, Radar engineering revised edition, 11.5.2.

SUMMARY OF INVENTION

TECHNICAL PROBLEM [0004]

In the conventional radar apparatus, A/D converters are disposed respectively for antenna elements, as mentioned above . Therefore, a problem is that the H/W scale increases. A further problem is that when searching for targets in a plurality of directions, the amount of arithmetic operation required at a time of forming an antenna pattern in each of a plurality of directions becomes huge because of the digital signal processing.

[0005]

The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a radar apparatus that can reduce its H/W scale as compared with conventional configurations, and that can search for targets in a plurality of directions with a low amount of arithmetic operation.

SOLUTION TO PROBLEM [0006]

According to the present invention, there is provided a radar apparatus including: a pulse signal generating unit for generating a pulse signal; a transmitter unit for generating a transmission signal from the pulse signal generated by the pulse signal generating unit; a transmitting antenna element for radiating the transmission signal generated by the transmitter unit into space; a plurality of receiving antenna elements each for receiving, as a received signal, a signal which is radiated by the transmitting antenna element and is reflected by a target; a frequency converting unit for converting received signals received by the plurality of receiving antenna elements into received signals having mutually different frequencies; a synthesizer for synthesizing the received signals after the conversion performed by the frequency converting unit to generate a received video signal; an A/D converter for A/D converting the received video signal after the synthesis performed by the synthesizer; a time-to-frequency domain converter for converting a received video signal after the A/D conversion performed by the A/D converter into a received video signal in a frequency domain; a target-candidate detector for detecting a candidate for the target from the signal power of the received video signal after the conversion performed by the time-to-frequency domain converter; and a target-candidate direction calculator for calculating the direction pointing to the target candidate from a detection result acquired by the target-candidate detector.

ADVANTAGEOUS EFFECTS OF INVENTION [0007]

Because the radar apparatus according to the present invention is configured as above, the H/W scale can be reduced as compared with conventional configurations, and targets in a plurality of directions can be searched for with a low amount of arithmetic operation.

BRIEF DESCRIPTION OF DRAWINGS [0008]

Fig. lisa diagram showing an example of the configuration of a radar apparatus according to Embodiment 1 of the present invention;

Fig. 2 is a diagram showing an example of the hardware configuration of the radar apparatus according to Embodiment 1 of the present invention;

Fig. 3 is a flow chart showing an example of an operation of transmitting a transmission signal which is performed by the radar apparatus according to Embodiment 1 of the present invention;

Fig. 4 is a diagram showing an example of a relationship between a pulse repetition interval and a pulse width which are calculated by a parameter calculator in the radar apparatus according to Embodiment 1 of the present invention;

Fig. 5 is a diagram explaining an example of the influence of the relationship between the pulse repetition interval and the pulse width on discrete Fourier transform results, and Fig. 5A is a diagram showing an example in a case in which the pulse repetition interval is an integral multiple of the pulse width and Fig. 5B is a diagram showing an example in a case in which the pulse repetition interval is not an integral multiple of the pulse width;

Fig. 6 is a flow chart showing an example of an operation of receiving received signals which is performed by the radar apparatus according to Embodiment 1 of the present invention;

Fig. 7 is a diagram showing an example of a relationship among the phases of received signals received by antenna elements in the radar apparatus according to Embodiment 1 of the present invention;

Fig. 8 is an diagram showing an example of the interval between the received signals on which frequency conversion are performed by phase shifters in the radar apparatus according to Embodiment 1 of the present invention, and Fig. 8A is a diagram showing an example of the interval in a case of an angular frequency domain and Fig. 8B is a diagram showing an example of the interval in a case of a time domain;

Fig. 9 is a diagram showing an example of a received video signal after synthesis performed by a synthesizer in the radar apparatus according to Embodiment 1 of the present invention, and Fig. 9A is a diagram showing an example in a case in which no weight is assigned and Fig. 9B is a diagram an example in a case in which a weight (humming window) is assigned;

Fig. 10 is a flow chart showing an example of a signal processing operation performed by a signal processor in the radar apparatus according to Embodiment 1 of the present invention;

Fig. 11 is a diagram showing an example of a relationship between an angular frequency and a directional orientation in the radar apparatus according to Embodiment 1 of the present invention;

Fig. 12 is a diagram explaining an example of forming an antenna pattern which is changed with time in the radar apparatus according to Embodiment 1 of the present invention;

Fig. 13 is a diagram explaining an example of the influence of a relationship between the period of the angular frequency and the pulse width on the distance measurement performance;

Fig. 14 is a diagram showing an example of processing results provided by the radar apparatus according to Embodiment 1 of the present invention;

Fig. 15 is a diagram showing an example of the configuration of a radar apparatus according to Embodiment 2 of the present invention; and

Fig. 16 is a diagram explaining an example of the influence of a relationship between a pulse repetition interval and a pulse width on discrete Fourier transform results.

DESCRIPTION OF EMBODIMENTS [0009]

Hereafter, the preferred embodiments of the present invention will be explained in detail with reference to the drawings .

Embodiment 1.

Fig. lisa diagram showing an example of the configuration of a radar apparatus according to Embodiment 1 of the present invention.

The radar apparatus includes a transmitter 1, a receiver 2, a signal processor 3 and a display device 4, as shown in Fig.

1.

[0010]

The transmitter 1 has a transmitter unit 101 and an antenna element (transmitting antenna element) 102.

[0011]

The transmitter unit 101 generates a transmission signal using a pulse signal received from a pulse modulator 203 which is disposed in the receiver 2 and which will be described below. The transmission signal generated by this transmitter unit 101 is outputted to the antenna element 102.

[0012]

The antenna element 102 radiates the transmission signal (radio wave) from the transmitter unit 101 into space.

[0013]

The receiver 2 has a local oscillator 201, a parameter calculator 202, the pulse modulator (pulse signal generating unit) 203, a plurality of antenna elements (receiving antenna elements) 204 (204-1 to 204-M), a plurality of phase shifters (frequency converting unit) 205 (205-1 to 205-M) , a synthesizer 206, a mixer 207 and a single A/D converter 208.

[0014]

The local oscillator 201 generates a local oscillation signal. The local oscillation signal generated by this local oscillator 201 is outputted to the pulse modulator 203 and the mixer 207.

[0015]

The parameter calculator 202 calculates a pulse repetition interval (PRI) and a pulse width which are parameters of the pulse signal generated by the pulse modulator 203. The parameter calculator 202 also calculates an angular frequency, which is used by the phase shifters 205, from the pulse width calculated thereby. Pieces of information showing the pulse repetition interval and the pulse width which are calculated by this parameter calculator 202 are outputted to the pulse modulator 203, and information showing the calculated angular frequency is outputted to each of the phase shifters 205. The information showing the pulse repetition interval is also outputted to a time-to-frequency domain converter 301 which is disposed in the signal processor 3 and which will be described below.

[0016]

The pulse modulator 203 pulse-modulates the local oscillation signal from the local oscillator 201 in accordance with the pieces of information sent from the parameter calculator 202 and showing the pulse repetition interval and the pulse width, to generate a pulse signal. The pulse signal generated by this pulse modulator 203 is outputted to the transmitter unit 101 of the transmitter 1.

[0017]

Each antenna element 204 receives, as a received signal, a signal which is radiated by the transmitter unit 101 of the transmitter 1 and is reflected by a target which is an observation object. The received signal received by each antenna element 204 is outputted to the corresponding phase shifter 205.

In this embodiment, the antenna element 102 for radiating the transmission signal and the antenna elements 204 each for receiving a received signal are configured as different elements. As an alternative, the antenna element 102 and the antenna elements 204 can be configured integrally. More specifically, by using a common antenna element, a transmission signal can be radiated when transmitting this signal and a received signal can be received when receiving this signal. [0018]

The plurality of phase shifters 205 are disposed respectively for the plurality of antenna elements 204, and each of the phase shifters shifts the phase of the received signal from the corresponding antenna element 204, thereby converting the received signals into received signals whose frequencies are different from one another among the plurality of antenna elements 204. At that time, each phase shifter 205 calculates a phase shift amount (frequency changing amount) from the information sent from the parameter calculator 202 and showing the angular frequency, and shifts the phase of the received signal in accordance with this phase shift amount. The received signal on which frequency conversion is performed by each phase shifter 205 is outputted to the synthesizer 206.

[0019]

The synthesizer 206 synthesizes the received signals from the phase shifters 205, to generate a received video signal. When reducing the sidelobes of the antenna pattern, the synthesizer 206 carries out the synthesis after assigning the received signal from each phase shifter 205 a weight corresponding to the corresponding antenna element 204. The received video signal generated by this synthesizer 206 is outputted to the mixer 207.

[0020]

The mixer 207 downconverts the received video signal from the synthesizer 206 by using the local oscillation signal from the local oscillator 201. A received video signal after the downconversion performed by this mixer 207 is outputted to the A/D converter 208.

[0021]

The A/D converter 208 A/D converts the received video signal from the mixer 207 by performing phase detection on the received video signal. A received video signal after the A/D conversion performed by this A/D converter 208 is outputted to the time-to-frequency domain converter 301 which is disposed in the signal processor 3 and which will be described below. [0022]

The signal processor 3 has the time-to-frequency domain converter 301, a target-candidate detector 302, a target-candidate direction calculator 303, a target-candidate relative-velocity calculator 304 and a target-candidate relative-distance calculator 305.

[0023]

The time-to-frequency domain converter 301 converts the received video signal from the A/D converter 208 of the receiver 2 into a received video signal in a frequency domain in accordance with the information sent from the parameter calculator 202 of the receiver 2 and showing the pulse repetition interval. The received video signal in the frequency domain after the conversion performed by this time-to-frequency domain converter 301 is outputted to the target-candidate detector 302. This received video signal is also outputted to the display device 4 via the target-candidate detector 302, the target-candidate direction calculator 303, the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0024]

The target-candidate detector 302 detects a candidate for a target in accordance with the signal power of the received video signal from the time-to-frequency domain converter 301. Information showing the target candidate detected by this target-candidate detector 302 is outputted to the target-candidate direction calculator 303, the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0025]

The target-candidate direction calculator 303 calculates the direction pointing to the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate. Information showing the direction pointing to the target candidate calculated by this target-candidate direction calculator 303 is outputted to the display device 4 via the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0026]

The target-candidate relative-velocity calculator 304 calculates the relative-velocity of the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate. Information showing the relative-velocity of the target candidate calculated by this target-candidate relative-velocity calculator 304 is outputted to the display device 4 via the target-candidate relative-distance calculator 305.

[0027]

The target-candidate relative-distance calculator 305 calculates the relative distance of the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate. Information showing the relative distance of the target candidate calculated by this target-candidate relative-distance calculator 305 is outputted to the display device 4.

[0028]

The display device 4 outputs the pieces of information sent from the signal processor 3 on a screen thereof as processing results.

[0029]

Next, an example of a hardware configuration for implementing the radar apparatus configured as above will be explained with reference to Fig. 2.

The hardware configuration of the radar apparatus is comprised of a transmitter device 51, a receiver device 52, a processor 53, a memory 54 and a display 55, as shown in, for example, Fig. 2.

[0030]

In this configuration shown in Fig. 2, the transmitter 1 shown in Fig. 1 is implemented by the transmitter device 51. Further, the receiver 2 shown in Fig. 1 is implemented by the receiver device 52 . Further, the display device 4 shown in Fig. 1 is implemented by the display 55. Further, the signal processor 3 shown in Fig. 1 is implemented by the processor 53 that executes a program stored in the memory 54. Further, a plurality of processors 53 and a plurality of memories 54 can perform the above-mentioned functions in cooperation with each other .

[0031]

Next, operations of the radar apparatus according to Embodiment 1 will be explained.

First, an operation of transmitting a transmission signal will be explained with reference to Fig. 3.

In the operation of transmitting a transmission signal, the local oscillator 201 generates a local oscillation signal Lo(t) in accordance with the following equation (1), first (step ST301), as shown in Fig. 3.

In this equation, t denotes a time, T_obs denotes an observation time of the radar apparatus, to denotes the frequency of the local oscillation signal L_o (t), and A_L denotes the amplitude of the local oscillation signal Lo(t) . The local oscillation signal Lo(t) generated by this local oscillator 201 is outputted to the pulse modulator 203 and the mixer 207. [0032]

Further, the parameter calculator 202 calculates the pulse repetition interval T_PRI and the pulse width T_pi_s which are parameters of the pulse signal (step ST302). In Embodiment 1, as shown in Fig. 4, the pulse repetition interval T_PRI is set to an integral multiple of the pulse width T_pi_s in accordance with the following equation (2).

T — Λ’ T ¹ PRl ~ RT-¹ ph

In this equation, N_int is a positive integer. The pieces of information showing the pulse repetition interval T_PRI and the pulse width T_pi_s which are calculated by this parameter calculator 202 are outputted to the pulse modulator 203. The information showing the pulse repetition interval T_PRI is also outputted to the time-to-frequency domain converter 301 of the signal processor 3.

[0033]

The parameter calculator 202 also calculates the angular frequency ω from the calculated pulse width T_pi_s (step ST303). At this time, the parameter calculator calculates the angular frequency ω in which a time period T during which its phase goes around once is equal to the pulse width T_pi_s, in accordance with ( 3 ) denotes the frequency interval whose frequencies are converted Information showing the angular frequency ω calculated by this parameter calculator 202 is outputted to each phase shifter 205.

[0034]

Even when the received signals are converted into 25 received signals having different frequencies by the phase shifters 205 by calculating the pulse repetition interval T_PRIand the pulse width T_pi_s, which satisfy the equation (2), and the angular frequency ω, which satisfies the equation (3), as the following equation (3,

2π 2π

- ραΐΐί this equation, At between the received signals by the phase shifters 205.

mentioned above, the received signals become coherent during one pulse repetition interval (during a time interval between ai and a₂ shown in Fig. 5) , as shown in Fig. 5A, and are therefore oriented toward the same direction. Therefore, when the time-to-frequency domain converter 301 performs a discrete Fourier transform on this received video signal at intervals of the pulse repetition interval T_PRI, the received video signal is integrated coherently for the Doppler frequency (relative-velocity) of the target candidate. Fig. 5 is a diagram showing a relationship between the pulse signal and frequency-converted received signals . In this Fig. 5, a dashed dotted line shows a received signal whose frequency is converted into a frequency 1ω, and a broken line shows a received signal whose frequency is converted into a frequency 2ω.

[0035]

On the other hand, when the equations (2) and (3) are not satisfied simultaneously, the received signals become non-coherent during one pulse repetition interval, as shown in Fig. 5B. Therefore, even when the time-to-frequency domain converter 301 performs a discrete Fourier transform on this received video signal at intervals of the pulse repetition interval T_PRI, the received video signal is not integrated coherently for the Doppler frequency (relative-velocity) of the target candidate, and other components are also integrated. As a result, it becomes difficult to calculate the relative-velocity of the target candidate.

[0036]

The pulse modulator 203 then pulse-modulates the local oscillation signal Lo(t) from the local oscillator 201 in accordance with the pieces of information sent from the parameter calculator 202 and showing the pulse repetition interval T_PRI and the pulse width T_pi_s, and in accordance with the following equations (4) and (5) , to generate a pulse signal Lpis(t) (step ST304) .

ijtl· <'A_l exph'T,,.,, < t < hT_m + 0, otherwise

V (/7 = 0,1,---,//-1) (4 ) (5) !’!?/

In these equations, h denotes a hit number, and H denotes the number of hits. The pulse signal L_pi_s(t) generated by this pulse modulator 203 is outputted to the transmitter unit 101 of the transmitter 1.

[0037]

The transmitter unit 101 then generates a transmission signal using the pulse signal L_pi_s(t) received from the pulse modulator 203 of the receiver 2 (step ST305) . The transmission signal generated by this transmitter unit 101 is outputted to the antenna element 102.

The antenna element 102 then radiates the transmission signal from the transmitter unit 101 into space (step ST306). [0038]

Next, an operation of receiving a received signal will be explained with reference to Fig. 6.

In the operation of receiving a received signal, each antenna element 204 receives, as a received signal, a signal which is radiated by the transmitter unit 101 of the transmitter

1 and is reflected by a target, first (step ST601), as shown in Fig. 6. Hereafter, it is assumed that a uniform linear array is provided as the plurality of antenna elements 204. It is further assumed that the target has a direction Θ, a relative distance Ro and a relative-velocity v. Further, the received signal Rx_m(t) received by each antenna element 204 is expressed by the following equation (6).

Rx_m (/) = (/ )exp }2π/₀ sin //J (0</<7;J (6) (m - 1,2,·>ΛΤ)

In this equation, Rx₀(t) denotes the received signal of an antenna element 204 located at a reference point, M denotes the number of antenna elements 204, m denotes the number of each antenna element 204, d denotes the interval between adjacent antenna elements 204, and c denotes the velocity of light. [0039]

Further, the received signal Rxo (t) of the antenna element 204 located at the reference point is expressed by the following equation (7).

W4=Λ, ^exp( I ₍₇)

In this equation, A_Rx denotes the amplitude of the received signal Rxo (t) . A relationship among the phases of the received signals received by the antenna elements 204 is shown in Fig.

7.

The received signal Rx_m(t) received by each antenna element 204 is outputted to the corresponding phase shifter 205 . [0040]

Then, each phase shifter 205 shifts the phase of the received signal Rx_m(t) from the corresponding antenna element 204, thereby converting the received signals into received signals whose frequencies are different from one another among the antenna elements 204 (step ST602) . At this time, each phase shifter 205 calculates a phase shift amount <%, _m(t) from the information sent from the parameter calculator 202 and showing the angular frequency ω, in accordance with the following equation (8) , and shifts the phase of the received signal Rx_m(t) .

< k·.: (0 ·“ 4· W (“ ./(« “ ί M = 4 exp (- j2x{m -) . , x ’ 'lb / (o s ι< n„)

MVsM)

In this equation, A_c denotes the amplitude of the phase shift amount <%, _m (t) , and ω denotes the angular frequency between the received signals (Fig. 8) which is shown by the equation (3) .

[0041]

Further, the received signal Rx^, _m(t) on which the frequency conversion is performed is expressed by the following equation ( 9) .

2(7?_O - w) f / , (« •••iV .

exp] ; -2,-.,4-* 2¾ hT_nef + < t < hT^ + —a. * _Tnfr c c

0, otherwise , (., ,(. 2ί4-ν4ϊι f., f . _ ,

4,. exp] | _exp j2xl - ,f_it~-- sin & + - Ι /Δ// ,

V ' \ ^e Λ/ L v ~ ^€' '' J J hT_w + + c c

0, tfj&erW'ise ((}</<?;□ (w ~ 1,2,', Λ

In this equation, * denotes complex conjugate,

The received signal Rx^, _m(t) on which the frequency conversion is performed by each phase shifter 205 is outputted to the synthesizer 206.

[0042]

Then, the synthesizer 206 synthesizes the received 5 signals Rx^, _m(t) from the phase shifters 205, to generate a received video signal (step ST603) . The received video signal Rx^, sum (t) after the synthesis performed by this synthesizer 206 is expressed by the following equation (10).

Λ, exp I /2zr/₀ Z-v ( 1

2(Z · vzi

V exp J /\ - ——— sin Θ + (m -1 Rot j I,

Ζί V l c ^{! 1} , 2R₀ , „ 2R_n hT,_Rl + ~~^<t< hi™ +~~PL + T, mi pis

0, otherwise ) Σ2 ^exP f Y ^2/rf Λ sin Θ + (m - \)kft ] |, w«l

IR 7R hT_PRl +^<t<hT_Mi, + + ;0, otherwise to * > < r„)

PM ’ ‘ *' pis

C C (10) [0043]

Further, when reducing the sidelobes of the antenna pattern, the synthesizer 206 carries out the synthesis after assigning the received signal Rx^, _m(t) from each phase shifter 205 a weight w_m corresponding to the corresponding antenna element 204. As the weight w_m, a humming window or the like is set in accordance with the sidelobe levels, the signal to noise ratio, or the like.

In this case, the received video signal Rx^, _sum(t) is expressed by the following equation (11).

^,„,«(0=ΣΟηΑ,,,Μ) w=i (11)

By carrying out the synthesis after assigning the received signal Rx^, _m(t) the weight w_m, there is provided an advantage of reducing the sidelobes of the antenna pattern, as shown in Fig. 9B, as compared with a case, as shown in Fig. 9A, in which no weight w_m is assigned to the received signal.

The received video signal Rx^, _sum(t) generated by this synthesizer 206 is outputted to the mixer 207.

[0044]

The mixer 207 then downconverts the received video signal Rx^, sum (t) from the synthesizer 206 by using the local oscillation signal Lo (t) received from the local oscillator 201 (step ST604) . A received video signal V(t) after the downconversion performed by this mixer 207 is expressed by the following equation (12).

uo=.fc,,„„wA(f) exp

Vexpl /2^1 - —— sin0 + («-l)A/?

¹' ¹ c y (12) hr ₊ .²V. <_t<hT + +τ ft A. PRI · t ft A r>i>_f t i A 'MV

0, otherwise (us'-Vd

In this equation, A_v denotes the amplitude of the received 20 video signal V(t). The received video signal V(t) after the downconversion performed by this mixer 207 is outputted to the

A/D converter 208.

[0045]

The A/D converter 208 then performs A/D conversion on the received video signal V(t) from the mixer 207 by performing phase detection on the received video signal (step ST605). A received video signal V (h, n) after the A/D conversion performed by this A/D converter 208 is expressed by the following equation (13) .

1(/7,/7)

A- exp /2/r/₀

2(/?_u - v(hT_m + «Δ/))'

Vexpi y'2/ΤΪ - ™ sin Θ + (m I. V ‘ C ' jj _{(1 3)} i rr, 2// , 2R_n /i/™_r -t--< t < hT_PR! -I---l· T,

PR!

C

0, otherwise (// = 0,1,---,//-1) (/7 = 0,1, ···,¥-!) ph:

In this equation, N denotes the number of samplings within one pulse repetition interval, n denotes a sampling number within one pulse repetition interval, and ΔΤ denotes a sampling interval within one pulse repetition interval. The received video signal V (h, n) after the A/D conversion performed by this

A/D converter 208 is outputted to the time-to-frequency domain converter 301 of the signal processor 3.

[0046]

Next, a signal processing operation performed by the signal processor 3 will be explained with reference to Fig. 10.

In the signal processing operation performed by the signal processor 3, first, the time-to-frequency domain converter 301 converts the received video signal V(h, n) from the A/D converter 208 of the receiver 2 into a received video signal in the frequency domain in accordance with the information sent from the parameter calculator 202 and showing the pulse repetition interval T_PRI (step ST1001), as shown in

Fig. 10. The received video signal fd, v(k, n) in the frequency domain after the conversion performed by this time-to-f requency domain converter 301 is expressed by the following equation (14) .

(k,n) = n)exp

(k = 0,1,--I) (« = 0,1, ¢14)

In this equation, H_FFT denotes the number of conversion points in the frequency domain, and k denotes a sampling number in the frequency domain. The received video signal fd, v(k, n) in the frequency domain after the conversion performed by this time-to-frequency domain converter 301 is outputted to the target-candidate detector 302, and is also outputted to the display device 4 via the target-candidate detector 302, the target-candidate direction calculator 303, the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0047]

The time-to-frequency domain converter 301 performs a discrete Fourier transform at intervals of the pulse repetition interval T_PRI, thereby converting the received video signal into a received video signal in the frequency domain. Therefore, this converting operation provides an effect of performing coherent integration on the received video signal, and provides an advantage of improving the signal to noise ratio (SNR) . In this embodiment, although the converting operation is explained using a discrete Fourier transform as the frequency domain conversion, a fast Fourier transform can be alternatively used. [0048]

Further, when expanding the equation (14), the following equation (15) can be acquired.

Λ,,.- (k, w) = Ay £ exp I ,/2/ri - f₀ sin Θ + [m - l}^f{hT_PRJ + ζ?Δί) λ:-]

H-\

Σ^εχρ h ²U> ~^iT_M c j f (m -- 1)4 ,,

-k

CXp ~~ '1 ±71---------------K) t ,

A,, exp | ./2^-ρ,/θ.........-•sin + + «Δί) exp j2?cj\ ( 2(//,, - vnAt) y/~j

Eexp

FFT

E^expf./2/T( ~/₀™—^sin0 + (/«+«Δ/) exp j ]2π/_ϋ f 2(&,-ν«Δ/)Υ^ ⁽ p^-y:—“IE®* / Αχ-O /2ττ| ./^-/ y V c H _CT:.

(15) [0049]

It can be seen from this equation (15) that terms associated with the frequency conversion exist as shown in the following expressions (16) and (17).

εχρΟ'2^(/?/-ΐ)Δ#ζΓ,.._Λ/) (1 7) [0050]

In these expressions, because the equation (3) shows

Af=l/Tpi_s, and the pulse repetition interval T_PRI is an integral multiple N_int of the pulse width, the expression (17) is expressed as shown by an expression (18) . Therefore, even if the hit number h or the antenna element number M, which is an integer, changes, a change in the exponent of the expression is simply an integral multiple of 2n, and no influence is exerted on the result of the frequency domain conversion (discrete Fourier transform) . More specifically, the Doppler frequency (relative-velocity) can be determined correctly even if the receiver converts the received signals from the plurality of antenna elements 204 into received signals having different frequencies by using the parameter calculator 202. More specifically, as shown in Fig. 14, the received video signal can be integrated so as to provide the relative-velocity of a target candidate, and this relative-velocity exhibits a maximum.

exp (./2tt(w - ) = expl ]2π(η ( * pis = exp(/2zr(m -1 ) (18) [0051]

The target-candidate detector 302 then detects a target candidate in accordance with the signal power of the received video signal fd, v(k, n) from the time-to-frequency domain converter 301 (step ST1002) . At this time, the target-candidate detector 302 detects a target candidate by performing, for example, a CFAR (Constant False Alarm Rate) process. Information showing the target candidate detected by this target-candidate detector 302 (pieces of information showing a sampling number k' of the target candidate in the frequency domain and a sampling number n' of the target candidate within one pulse repetition interval) is outputted to the target-candidate direction calculator 303, the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0052]

Hereafter, an effect produced by the receiver 2 according to the present invention will be explained.

The phase shifters 205 of the receiver 2 convert the frequencies of the received signals into frequencies which are different from one another by the angular frequency ω. This frequency conversion means that the phases among the received signals are controlled in such a way that the phases are different from one another by an integral multiple of ωΤ, as shown in the equations (8) and (9). More specifically, by converting the frequencies of the received signals into frequencies which are different from one another by the angular frequency ω, the directional orientation of the antenna pattern can be changed with time, as shown in Figs. 11 and 12. As a result, it is not necessary to form an antenna pattern for each direction, unlike in the case of conventional radar apparatuses, and multi-beam data for which the amount of arithmetic operation is reduced can be acquired. In Fig. 11, A denotes a phase front at a time t, A' denotes a phase front at a time t+At, Di denotes a distance corresponding to a phase ωί, D_m-i denotes a distance corresponding to a phase (Μ-Ι)ωί, and D'_m-i denotes a distance corresponding to a phase (M-l)ω(t+At). In Fig. 12, a reference numeral 1201 denotes the antenna pattern.

[0053]

In the equation (15), a term associated with a time direction within one pulse repetition interval is shown by an equation (19), and, when an equation (20) is satisfied, the beam (antenna pattern) can be oriented toward a direction Θ. In Embodiment 1, by converting the frequencies of the received signals into frequencies which are different from one another by the angular frequency ω (=2nhf) , a beam can be formed in such a way as to be changed with time. Therefore, as shown in Fig. 14, a relationship between the time t and the direction Θ becomes clear, and it becomes possible to calculate the direction θ of the beam (antenna pattern) at the time t in accordance with an equation (21).

exp ^/2^- f₀ ——— sin Θ + (m -

5g ^exP ί j2zr| - /₀ — sin Θ + AfiAt -1) — sin Θ + Mi At - 0 c (20) = sin c

fjd λ

AfiAt

J (2 1) [0054]

The target-candidate direction calculator 303 then 15 calculates the direction θ' of the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate (the sampling number n' of the target candidate within one pulse repetition interval), and in accordance with the following equation (22) (step ST1003) .

= sin ’ -^-AfirAt (22)

The information showing the direction θ' of the target candidate calculated by this target-candidate direction calculator 303 is outputted to the display device 4 via the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305.

[0055]

Further, the target-candidate relative-velocity calculator 304 calculates the relative-velocity ν' of the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate (sampling number k' of the target candidate in the frequency domain), and in accordance with the following equations (23) and (24) (step ST1004).

= <2 3)

Λν

In these equations, Av_samp denotes a velocity sampling interval. Information showing the relative-velocity ν' of the target candidate calculated by this target-candidate relative-velocity calculator 304 is outputted to the display device 4 via the target-candidate relative-distance calculator

305.

[0056]

Further, the target-candidate relative-distance calculator 305 calculates the relative distance Ro' of the target candidate in accordance with the information sent from the target-candidate detector 302 and showing the target candidate (sampling number n' of the target candidate within one pulse repetition interval), and in accordance with the following equation (25) (step ST1005).

z

J (25)

In this equation, floor (Z) is an integer which is equal to or smaller than a variable Z and which is the nearest to the variable Z. Information showing the relative distance Ro' of the target candidate calculated by this target-candidate relative-distance calculator 305 is outputted to the display device 4.

[0057]

In this embodiment, the parameter calculator 202 sets the time period T during which the phase of the angular frequency ω goes around once as the pulse width T_pi_s. Therefore, the radar apparatus can carry out the distance measurement and the direction measurement while eliminating ambiguity in the distance, as shown in Fig. 13A. Further, the radar apparatus can calculate the number of target candidates nonerroneously. In contrast, when the time period T during which the phase of the angular frequency ω goes around once is not set as the pulse width Tpi_s, distance ambiguity occurs and the performance of the distance measurement gets worse. Further, because the angular frequency ω becomes high in the example of Fig. 13B, the sampling frequency also becomes high and the amount of arithmetic operation increases.

[0058]

After that, the display device 4 outputs the pieces of information from the signal processor 3 (the received video signal fd, v(k, n), the direction θ' of the target candidate, the relative-velocity ν' of the target candidate and the relative distance Ro' of the target candidate) onto the screen as processing results.

[0059]

As mentioned above, because the radar apparatus according to Embodiment 1 is configured so as to convert received signals received by the antenna elements 204 into received signals having mutually different frequencies, the synthesizer 206 can be disposed and A/D converts to be disposed can be limited to the single A/D converter 208, the H/W scale can be reduced as compared with conventional configurations, and targets in a plurality of directions can be searched for with a low amount of arithmetic operation.

[0060]

Further, because the pulse modulator 203 generates a pulse signal whose pulse repetition interval is an integral multiple of its pulse width, each phase shifter 205 calculates a phase shift amount by using an angular frequency in which a time period during which its phase goes around once is equal to the pulse width, and performs frequency conversion, and the time-to-frequency domain converter 301 performs conversion into a signal in the frequency domain at intervals of the pulse repetition interval, the radar apparatus can calculation the relative-velocity of a target candidate.

[0061]

In the above-mentioned embodiment, the radar apparatus converts the received signals received by the antenna elements 204 into received signals having mutually different frequencies by using the plurality of phase shifters 205. However, the frequency converting unit has only to be able to convert the received signals received by the antenna elements 204 into received signals having mutually different frequencies, and is limited to the above-mentioned example. For example, as the frequency converting unit, a plurality of local oscillators disposed respectively for the antenna elements 204, for generating local oscillation signals having mutually different frequencies, and a plurality of mixers disposed respectively for the antenna elements 204, each for performing frequency conversion by downconverting the received signal received by the corresponding antenna element 204 by using the local oscillation signal generated by the corresponding local oscillator can be used.

[0062]

Further, the example in which the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305 are disposed in the radar apparatus shown in Fig. 1 is shown above. However, the target-candidate relative-velocity calculator 304 and the target-candidate relative-distance calculator 305 are not indispensable components, these units do not have to be disposed in a case in which it is not necessary to calculate the relative-velocity and the relative distance of a target candidate .

[0063]

Embodiment 2 .

Fig. 15 is a diagram showing an example of the configuration of a radar apparatus according to Embodiment 2 of the present invention. In the radar apparatus according to Embodiment 2 shown in Fig. 15, the receiver 2 of the radar apparatus according to Embodiment 1 shown in Fig. 1 is changed to a receiver 2b, and the signal processor 3 of the radar apparatus is changed to a signal processor 3b. In this receiver

2b, the parameter calculator 202 of the receiver 2 according to Embodiment 1 shown in Fig. 1 is changed to a parameter calculator 202b. Further, in the signal processor 3b, the time-to-frequency domain converter 301 of the signal processor 3 according to Embodiment 1 shown in Fig. 1 is changed to a time-to-f requency domain converter 301b. The other components are the same as those according to Embodiment 1, and are denoted by the same reference numerals and the explanation of the components will be omitted hereafter.

[0064]

The parameter calculator 202b calculates parameters (a pulse repetition interval and a pulse width) of a pulse signal, and an angular frequency, like the parameter calculator 202 according to Embodiment 1. At this time, the pulse repetition interval does not have to be an integral multiple of the pulse width. The parameter calculator 202b also performs calculation of a time interval which is the least common multiple of the pulse repetition interval and the pulse width. Pieces of information showing the pulse repetition interval and the pulse width which are calculated by this parameter calculator 202b are outputted to a pulse modulator 203, information showing the calculated angular frequency is outputted to each of phase shifters 205, and information showing the calculated time interval is outputted to the time-to-f requency domain converter 301b of the signal processor

3b.

[0065]

The time-to-frequency domain converter 301b converts a received video signal from an A/D converter 208 of the receiver 2b into a received video signal in a frequency domain by performing a Fourier transform (discrete Fourier transform or fast Fourier transform) on the received video signal at intervals of the above-mentioned time interval, in accordance with the information sent from the parameter calculator 202b and showing the time interval. The received video signal in the frequency domain after the conversion performed by this time-to-frequency domain converter 301b is outputted to a target-candidate detector 302. This received video signal is also outputted to a display device 4 via the target-candidate detector 302, a target-candidate direction calculator 303, a target-candidate relative-velocity calculator 304 and a target-candidate relative-distance calculator 305.

[0066]

In Embodiment 2, the parameter calculator 202b calculates the pulse repetition interval T_PRI and the pulse width T_pi_s which satisfy the equation (2), and the angular frequency ω which satisfies the equation (3), and further calculates the time interval T_Lcm which is the least common multiple of the pulse repetition interval T_PRI and the pulse width T_pi_s, in accordance with an equation (26) .

Tum ~ LCM{t_pjii ,T_p!s) ( 2 6 )

In this equation, LCM(A, B) is the least common multiple of a variable A and a variable B.

[0067]

Then, the time-to-frequency domain converter 301b converts the received video signal V (h, n) from the A/D converter 208 of the receiver 2b into a received video signal fd, v(k, n) in the frequency domain, in accordance with the equation (14) . In Embodiment 2, the time-to-frequency domain converter performs a Fourier transform at intervals of, instead of the pulse repetition interval T_PRI, the time interval T_LCm which is the least common multiple of the pulse repetition interval T_PRI and the pulse width T_pi_s.

[0068]

It is assumed in this Embodiment 2 that the pulse repetition interval T_PRI is a nonintegral multiple of the pulse width Tpi_s. In this case, as shown in Fig. 16, because the received signals are not coherent during one pulse repetition interval (during a time interval between ai and a₂ shown in Fig. 16) , even when the time-to-f requency domain converter performs a Fourier transform at intervals of the pulse repetition interval T_PRI, the received video signal cannot be integrated so as to provide only the relative-velocity of the target candidate, and therefore the relative-velocity cannot be calculated correctly.

In contrast, the received signals are coherent during one time interval T_Lcm which is the least common multiple of the pulse repetition interval T_PRI and the pulse width T_pi_s (during a time interval between a₂ and a3 shown in Fig. 16) . Therefore, because the time-to-f requency domain converter according to Embodiment 2 performs a Fourier transform at intervals of this time interval T_LCm< the received video signal can be integrated so as to provide only the relative-velocity of the target candidate, and therefore the relative-velocity can be calculated correctly.

[0069]

As mentioned above, because the radar apparatus according to this Embodiment 2 is configured so as to perform a Fourier transform on the received signal at intervals of the time interval which is the least common multiple of the pulse repetition interval and the pulse width, the radar apparatus can calculate the relative-velocity of a target candidate even when the pulse repetition interval is a nonintegral multiple of the pulse width, unlike the radar apparatus according to

Embodiment 1.

[0070]

While the invention has been described in its preferred embodiments, it is to be understood that an arbitrary combination of two or more of the above-mentioned embodiments can be made, various changes can be made in an arbitrary component in accordance with any one of the above-mentioned embodiments, and an arbitrary component in accordance with any one of the above-mentioned embodiments can be omitted within the scope of the invention.

INDUSTRIAL APPLICABILITY [0071]

The radar apparatus according to the present invention is suitable for use as a radar apparatus or the like that can reduce its H/W scale as compared with conventional configurations, and that can search for targets in a plurality of directions with a low amount of arithmetic operation, thereby being able to improve the target detection performance, to find out targets.

REFERENCE SIGNS LIST [0072]

1: transmitter; 2, 2b: receiver; 3, 3b: signal processor; 4: display device; 51: transmitter device; 52: receiver device; 53: processor; 54: memory; 55: display; 101: transmitter unit; 102: antenna element (transmitting antenna element) ; 201: local oscillator; 202, 202b: parameter calculator; 203: pulse modulator (pulse signal generating unit) ; 204: antenna element (receiving antenna element); 205: phase shifter (frequency converting unit); 206: synthesizer; 207: mixer; 208: A/D converter; 301, 301b: time-to-frequency domain converter; 302: target-candidate detector; 303: target-candidate direction calculator; 304: target-candidate relative-velocity calculator; and 305: target-candidate relative-distance calculator .

Claims

1. A radar apparatus comprising:

a pulse signal generating unit for generating a pulse signal;

a transmitter unit for generating a transmission signal from the pulse signal generated by said pulse signal generating unit;

a transmitting antenna element for radiating the transmission signal generated by said transmitter unit into space;

a plurality of receiving antenna elements each for receiving, as a received signal, a signal which is radiated by said transmitting antenna element and is reflected by a target;

a frequency converting unit for converting received signals received by said plurality of receiving antenna elements into received signals having mutually different frequencies;

a synthesizer for synthesizing the received signals after the conversion performed by said frequency converting unit to generate a received video signal;

an A/D converter for A/D converting the received video signal after the synthesis performed by said synthesizer;

a time-to-frequency domain converter for converting a received video signal after the A/D conversion performed by said A/D converter into a received video signal in a frequency domain;

a target-candidate detector for detecting a candidate for said target from signal power of the received video signal after the conversion performed by said time-to-frequency domain converter; and a target-candidate direction calculator for calculating a direction pointing to said target candidate from a detection result acquired by said target-candidate detector.

2. The radar apparatus according to claim 1, wherein said pulse signal generating unit generates said pulse signal whose pulse repetition interval is an integral multiple of a pulse width, said frequency converting unit performs said frequency conversion by using an angular frequency in which a time period during which its phase goes around once is equal to said pulse width, and said time-to-frequency domain converter performs a Fourier transform at intervals of said pulse repetition interval, thereby performing the conversion into a received video signal in said frequency domain.

3. The radar apparatus according to claim 1, wherein said frequency converting unit performs said frequency conversion by using an angular frequency in which a time period during which its phase goes around once is equal to a pulse width of said pulse signal, and said time-to-frequency domain converter performs a Fourier transform at intervals of a time length which is a least common multiple of a pulse repetition interval of said pulse signal and the pulse width.

4. The radar apparatus according to claim 2, wherein said frequency converting unit converts said received signals into received signals whose frequencies are different from one another by an integral multiple of said angular frequency.

5. The radar apparatus according to claim 3, wherein said frequency converting unit converts said received signals into received signals whose frequencies are different from one another by an integral multiple of said angular frequency.

6. The radar apparatus according to claim 1, wherein said frequency converting unit includes a plurality of phase shifters disposed respectively for said plurality of receiving antenna elements, each for shifting a phase of a received signal received by a corresponding one of said receiving antenna elements, thereby performing said frequency conversion.

7. The radar apparatus according to claim 1, wherein said frequency converting unit includes a plurality of local oscillators disposed respectively for said plurality of receiving antenna elements, for generating local oscillation signals having mutually different frequencies; and a plurality of mixers disposed respectively for said plurality of receiving antenna elements, each for downconverting a received signal received by a corresponding one of said receiving antenna elements by using a local oscillation signal generated by a corresponding one of said local oscillators, thereby performing said frequency conversion.

8. The radar apparatus according to claim 1, wherein said radar apparatus includes a target-candidate relative-velocity calculator for calculating a relative-velocity of said target candidate from the detection result acquired by said target-candidate detector.

9. The radar apparatus according to claim 1, wherein said radar apparatus includes a target-candidate relative-velocity calculator for calculating a relative distance of said target candidate from the detection result acquired by said

5 target-candidate detector.