WO1997019365A1

WO1997019365A1 - Radar device for a vehicle, particularly a motor vehicle

Info

Publication number: WO1997019365A1
Application number: PCT/FR1996/001823
Authority: WO
Inventors: Maurice Callac; Pascal Cornic; Nathalie Jan
Original assignee: Thomson-Csf
Priority date: 1995-11-21
Filing date: 1996-11-19
Publication date: 1997-05-29
Also published as: AU7629996A; FR2741453A1; FR2741453B1

Abstract

A radar device for a vehicle, particularly a motor vehicle, is disclosed. The device comprises a monopulse antenna (6) connected to transmitting means (1, 2, 3, 4, 5) transmitting at least two substantially pure sinusoidal waves (F0+F1, F0+F2) and means (7, 8, 9, 10, 11, 12, 13) for detecting the phase and amplitude of the signal received over the sum channel (Σ) relative to the intermediate-frequency signals (F1, F2), and detecting the phase and amplitude of the signal received over the difference channel (Δ) relative to at least one of the intermediate-frequency signals (F2). The device is useful as an alarm for warning of hazardous obstacles for motor vehicles.

Description

D1SPOSIΗF RADAR FOR A PARTICULARLY MOTOR VEHICLE

The present invention relates to a radar device for a vehicle. It applies in particular to the detection of dangerous obstacles on the trajectories of a passenger vehicle or a heavy vehicle to alert the driver and / or control the vehicle controls so as to avoid collision with the obstacle or still maintain a predetermined safety distance from the vehicle in front.

The solutions known in the abovementioned fields of application differ from one another by the way of ensuring the coverage of the observation area, which is in line with the choice of the principles of transmitting and receiving antennas on the one hand, and on the other hand by the way of obtaining the information of distance and speed, relating to the various radar targets to be treated, linked to the choice of the waveform of the radar.

With regard to the antenna, several solutions are known. A first, simple solution consists in using a fixed beam antenna in transmission and reception, according to a mono-static or bi-static principle. This solution, which has the advantage of simplicity, can be used in the context of high-speed and low-cost production.

However, it does not allow the angular location of targets and is therefore vulnerable to false alarms generated by the road infrastructure, in particular traffic signs, bridges or safety rails.

In addition, it does not allow tracking of targets in curved trajectories, in particular turns

The fixed beam antenna technique can therefore only be validly used in particular configurations such as, for example, applications with short range or with straight paths.

Another solution consists in sequentially using in transmission and in reception a small number of antennas, typically from 3 to 5, whose viewing directions are angularly offset with respect to each other, so as to provide overall coverage of the area. to observe.

This technique allows a coarse angular localization, limited by the beamwidth of the elementary antenna, typically equal to 3 degrees, and by its level of secondary lobes. Furthermore, it requires the use of microwave switches making it possible to ensure high decoupling between the signals received from the different antennas, which is a priori difficult to achieve, in particular in the field of millimeter waves. Finally, the performances are limited by the fact that the angular localization of the targets is carried out by comparison of average energy received in different directions, during different time intervals, which can be penalizing, for example in the presence of an effect. image in the azimuthal plane in certain operational configurations

Another solution consists in covering the observation area using a narrow beam antenna in the azimuth plane, typically less than 1 degree, this beam scanning the entire domain. This solution, although very effective, is difficult to envisage in the context of low-cost production, whether antenna scanning is obtained mechanically or electronically Another solution also consists in using simultaneously in transmission and in reception a small number of antennas whose viewing directions and / or the radiation patterns are different, so as to form, by linear combination of the signals received by the different antennas, a small number of beams allowing the precise angular location of the targets in the observation area The performances obtained by this principle is a direct function of the size of the network thus formed and therefore of the number of antennas used The number of v geese of reception and the volume of computation necessary to obtain the sufficient quality of information makes that this approach is difficult to apply to an automotive radar There is however a trivial implementation, called "monopulse", very frequently used in radar technique, which proves to be interesting for the application mentioned previously in the introduction, provided that the separation of the targets can be carried out by another channel than by the antenna itself This solution makes it possible, by emitting the same signal through two identical antennas, then by receiving the signal reflected simultaneously and independently on these two antennas, to precisely determine the angular position of a target in the area illuminated by the radar emission The monopulse technique is generally associated with a pulsed waveform, hence the name monopulse, or even with a continuous waveform.

Regarding the waveform, the solution generally used corresponds to pulse radar, Doppler or not, to FMCW radar, or to CW frequency-hopping radar.

Pulse radar is a powerful solution, provided it has a Doppler effect. In practice, the fineness of the pulses to be transmitted and the need to maintain the phase coherence of the received signal with respect to the transmitted signal, make it a costly and difficult solution, especially in the millimeter wave domain.

The FMCW radar requires, to reach a satisfactory level of performance, to transmit and receive broadband, on at least a hundred megahertz. This makes its realization complex. Furthermore, the distance / speed ambiguity resulting from this waveform makes it difficult to use radar signals when numerous targets are presented simultaneously in the area illuminated by the radar emission.

The CW frequency hopping radar is an interesting solution by its simplicity by making it possible to separate targets very finely thanks to a high Doppler resolution power. However, it has the disadvantage of controlling the microwave oscillator with great precision and with very short response times. On the other hand, this type of radar, produced in homodyne mode may have a decrease in sensitivity for low relative speeds, linked to the different noises of the active microwave elements such as in particular oscillators or mixers.

The main radar solutions implemented to date result from the different combinations of antenna techniques and waveforms mentioned above, with the advantages but also with the drawbacks associated therewith.

The object of the invention is to overcome these drawbacks. To this end, it combines the monopulse antenna technique with a waveform based on the simultaneous or sequential emission of two or more pure sinusoids. Consequently, the subject of the invention is a radar device for a vehicle, characterized in that it comprises a monopulse type antenna connected to transmission means emitting at least two waves having substantially the form of pure sinusoids, one wave being the sum of a microwave signal and an intermediate frequency signal, and means for detecting the amplitude and the phase of the signal received on the sum channel with respect to the intermediate frequency signals and for detecting the amplitude and the phase of the signal received on the difference channel with respect to at least one of the intermediate frequency signals. The main advantages of the invention are in particular that it is economical, that it is simple to implement, that it improves performance against noise, that it improves energy efficiency and that it offers better immunity to low frequency electromagnetic interference, especially due to the engine or mechanical vibrations of a vehicle.

Other characteristics and advantages of the invention will become apparent from the following description given with reference to the appended drawings which represent:

- Figure 1, an embodiment of a device according to the invention;

- Figure 2a and 3a, exemplary embodiments of frequency transposition means;

- Figures 2b and 3b, the waveforms generated by the above means. Figure 1 shows, by a block diagram, a possible embodiment of a device according to the invention. This device comprises a monopulse type antenna and means for emitting at least two waves having substantially the shape of a pure sinusoid. The association of a continuous sinusoidal waveform and the principle of transmission-reception monopulse makes it possible to locate angularly a large number of targets with a very low risk of confusion, these targets having been separated beforehand thanks to the power of resolution Very high radar Doppler. This solution according to the invention makes it possible, at low cost, to map the mobile echoes present at the front of the vehicle, as would a narrow beam scanning radar, the latter constituting on the contrary an expensive solution. The transmission means comprise for example a free microwave oscillator 1, operating for example at 77 GHz, connected to a mixer 2 for example of SSB type, that is to say with single sideband. This mixer is also connected to intermediate frequency oscillators 3. The frequency from the microwave oscillator 1 is transposed to these intermediate frequencies by means of the mixer 2. The frequency of the microwave oscillator is for example fixed. The frequency transposition can be carried out for example according to the modes presented in FIGS. 2a, 2b, 3a and 3b. FIG. 2a shows that the transposition to the frequency is achieved by simultaneously summing two or more sine waves F- ₎ , F ₂ substantially pure at the microwave frequency F ₀ of the microwave oscillator 1, the waves F- _j , F ₂ at intermediate frequency being, for example, summed together beforehand, a switch 201 separating the mixer from the addition device 202 of the waves.

FIG. 2b presents by two curves as a function of time the waveform of the signal emitted by its frequency and its amplitude, in the case where the frequency F ₀ is combined for example with two frequencies F _{1 (} F _2. FIG. 3a shows that the transposition can be carried out by alternating summing two or more sine waves F- |, F ₂ substantially pure at the frequency F ₀ .

FIG. 3b illustrates by two curves as a function of time the frequency and the amplitude of the transmitted wave. The amplitude remains the same from one recurrence to another, but the frequency is at a frequency F _Q + FJ one recurrence out of two, and at another frequency F ₀ + F ₂ , your other recurrences. In case of combination at N frequency, the frequency would be at a given frequency a recurrence on N.

The choice between one or the other type of transposition is made for example according to the constraints of realization, and / or considerations relating to the ambiguity distance from the radar.

Subsequently, by way of example, an embodiment is presented relating to the mode of transposition of FIGS. 2a and 2b.

FIG. 1 shows that the transmission means also comprise an amplification the input of which is connected to the output of the mixer 2, and a circulator 5 connected to the output of the amplifier 4. A magic tee separates for example the antenna 6, of the monopulse type, at the output of the circulator 5.

From the microwave oscillator 1 of frequency F ₀ , for example 77 GHz, and from the two or more, medium frequency oscillators of frequencies

and F ₂ for example 10 MHz and 10.250 MHz respectively, a wave is generated and transmitted on the sum channel Σ of the monopulse antenna 6. This transmitted wave consists of the sum of two sinusoids of respective frequencies F ₀ + F- | and F ₀ + F ₂ . The equation of the emitted wave e (t) is then established according to the following relation, in the case of combination with two sine waves: e (ή = a _l sm (2n {F _n + F _> ) t + a _i )

<r / _: sin (2π {F ₀ + F,) / + cc _z ) (l) a- | and a ₂ being the amplitudes of the sine waves.

On reception, the reflected signals relating to the different targets seen by the radar are received simultaneously on the two monopulse microwave channels, the sum channel Σ on the one hand, and the difference channel Δ on the other hand. The signals received on the sum channel Σ and the difference channel Δ being denoted respectively ∑ _r and Δ _r , these signals are defined according to the following relationships:

+ φ,)

+ Ε, a, sin (2π (^ + F + Fdήi - ^ (F, + F) + _φ:)} (2)

+ δ, a, s \ n (2π {F _(> + F + Fdi) t - ^ {F _n + F ₂ ) + φ _z )} (3)

Where: N represents the number of targets seen by the radar

Fdi represents the Doppler frequency corresponding to the i-th target di represents the distance of the i-th target from the radar

Z \ and δ _j represent the complex gains of the path Σ and the path Δ in the direction of the i th target a; represents the amplitude of the signal received from the i th target. The signals received on the channels Σ and difference Δ are demodulated by the microwave oscillator 1 at frequency F. For this purpose, the output of this oscillator 1 is connected to the input of two mixers 7, 8, the other input of which is connected to the sum channel Σ for one 7, and to the difference channel Δ for the other 8 Following this demodulation, the signals obtained at the output of these mixers are given by the following relationships ^•

+ ε _l a _l sm {24F ₂ + fdι) t - ² ηr ^L {Fo + F ₂ ) + <p 2)} (4)

+ ε, a, sm (2π (F _t: + fdι) ι - ^ {F ₀ + F ₂ ) + φ2)} (5)

] T being the signal from the sum channel, Δ _r being the signal from the difference channel, and K 'being an attenuation coefficient, less than a

These signals] T. , Δ. are for example amplified and filtered by bandpass amplifiers 9, 10 connected at output by mixers 7, 8

Amplitude and phase detection systems are produced at the output of the bandpass amplifiers to process the previous signals

∑ _r , Δ For this purpose, a first mixer 11 has one of its inputs connected to the first intermediate frequency oscillator F- | and its second input connected to the output of the first bandpass amplifier 9, processing the signal ∑ from the sum channel. A second mixer 12 has an input connected to the output of the second intermediate frequency oscillator F ₂ and its second input connected to the output of the first bandpass amplifier 9 Finally, a third mixer 13 has its first input connected to the second frequency oscillator intermediate F ₂ and its second input connected to the output of the second amplifier 10, processing the signal Δ _; from the difference path Thus, the phase and the amplitude of the signal ∑ _r received on the sum channel are detected with respect to the two signals at intermediate frequencies F- | and F ₂ , and the phase and the amplitude of the signal Δ received on the difference channel are detected with respect to any of the signals at intermediate frequency, that of the second oscillator for example, at frequency F ₂ . After low-pass filtering in the Doppler band carried out by means of low-pass amplifiers 14, 15, 16 connected to the outputs of the mixers 11, 12, 13, the following signals are obtained:

^ = K ^m & ε, has, if _n (2π / -ψ said _ϋ {F + F _t) ₊ ιr _n) (ό)

^ = K ^' lf _ι ε, a, sιn (2πfώt -ψ {F ₀ + F _î ) + ψ, _i ) (?)

K "being an attenuation coefficient, less than unity, ∑" _r <j being the signal relating to the sum channel combined at the intermediate frequency F1,

∑ " _r 2 being the signal relating to the sum channel combined in FIG. F2, and Δ" _r 2

(or R1) being ^an I signal concerning the combined difference channel is at the frequency F1 or frequency F2.

These signals ∑ " _r ι ∑" _r 2 Δ " _r 2 are then for example sampled and decoded by means of analog-digital converters 17, 18, 19 connected at the output of the low-pass amplifiers.

A battery of a number Q of Doppler filters 20 with narrow band connected to the output of the converters 17, 18, 19 makes it possible to filter the sampled signals. This battery of filters can for example be produced using a discrete Fourier transform.

Detection means 21 connected at the output of the filtering

Doppler 20 allow for example to detect the presence of a number P of targets by relative comparison and with respect to a threshold, of the output power of the various Doppler filters, this operation being able to be carried out on the sum channel ∑ and on the difference path Δ. Processing means 22 allow for example to estimate the speed of each of the P targets, knowing that the filter j is centered on the

2 Vi Doppler frequency fdj = - -, where Vj is the speed of the target detected relative to the radar, and λ is the wavelength of the radar. These processing means allow for example then:

- estimate the distance of each of the P targets by measuring the phase difference obtained between the channels ∑ _r - | and ∑ _r 2 at the output of the same Doppler filter where the target is detected, so as to form the phase difference A φi ≈ (F ^ - F,) where di is the distance from 'a th target to the radar, c being the speed of light;

- to estimate the angular position of each of the P targets by calculating the function below from the signals obtained at the output of the channels Δ _r ι and ∑ _r ι, or Δ _r 2 and ∑ _r 2 of the same Doppler filter where is detected the target, this function being: s θ. = Cartg- ±

'ε, where θ _j represents the angular position of the target considered in the azimuth plane, δj and εj having been defined previously;

- to deduce from the information previously estimated: distance, speed, angle and power of the Q targets detected, the target judged the most dangerous in relation to the trajectory of the vehicle;

- to transmit after filtering, through an interface 23, the distance, position and speed information relating to the target considered most dangerous, to a decision-making body capable of generating an alarm in the event of danger, or even of slaving the speed of the vehicle according to a known type of regulation ICC by the Anglo-Saxon expression

Intelligent Cruise Control.

The main advantages linked to the embodiment according to the invention arise in particular from the way of transmitting and receiving the radar signals. From the point of view of sensitivity and resolving power, the performance of the radar rests on the stability and the purity of the two sine waves at intermediate frequency Fj, F2 which can be easily generated using quartz. No particular performance is required with regard to the spectral purity and the medium-term stability of the microwave oscillator 1, which allows it to be produced at low cost using for example integrated components of the ASGA type, without setting implementation of an oscillator servo loop 1. The constraints on the purity and the precision of the supply of the microwave part are also relaxed.

On the other hand, the receiver operates in heterodyne mode, with an intermediate frequency for example of a few megahertz, which allows it in particular to overcome the noise factor varying inversely in proportion to the intermediate frequency. The receiver thus has an increased sensitivity compared to a solution in homodyne mode, where the intermediate frequency is zero, therefore the ratio 1 / Fi very large, Fi being the intermediate frequency The power emitted can therefore be reduced by as much, at performance equal

On the other hand, with the low power levels operating at intermediate frequency, the receiver then has better immunity to low frequency electromagnetic interference from the vehicle engine, and also to low frequency disturbances from mechanical vibrations of the chassis when the vehicle moves

Claims

1. Radar device for a vehicle, comprising an antenna (6) of the monopulse type connected to transmission means (1, 2, 3, 4, 5) emitting at least two waves (FQ + F ^, F0 + F2) having substantially the form of pure sinusoids, a wave being the sum of a microwave signal (FQ) and an intermediate frequency signal (F- |, F2), and means (7, 8, 9, 10, 11, 12, 13) to detect the amplitude and phase of the signal (∑ ' _r ) received on the sum channel (∑) with respect to the intermediate frequency signals (F ^, F2) and to detect the amplitude and phase of the signal (Δ ' _r ) received on the difference channel (Δ) with respect to at least one of the intermediate frequency signals (F2), characterized in that the microwave signals received on the sum (∑) and difference (Δ) channels are demodulated by the microwave oscillator (1, fo).

2. Device according to claim 1, characterized in that the demodulated signals (∑7-, Δ'r) are amplified and filtered by band pass amplifiers (9, 10).

3. Device according to any one of the preceding claims, characterized in that the substantially sinusoidal waves (Fo + F ^, Fo ⁺ F2) are transmitted simultaneously.

4. Device according to any one of claims 1 or 2, characterized in that the substantially sinusoidal waves (Fn + F-i, F0 + F2) are transmitted sequentially.

5. Device according to any one of the preceding claims, characterized in that the transmission means comprise at least one microwave frequency oscillator (1, FO), intermediate frequency oscillators (3) (F- _j , F2) delivering substantially pure sinusoids, a mixer (2), an amplifier (4), the outputs of the oscillators (1, 3) being connected to the inputs of the mixer (2), the output of the mixer being connected to the input of the amplifier ( 4).

6. Device according to any one of the preceding claims, characterized in that on reception, the sum channel (∑) is connected to an input of a first mixer (11) whose other input is connected to a first oscillator at a first intermediate frequency (F- |), and at the input of a second mixer whose other input is connected to the second oscillator at a second intermediate frequency (F2), and the difference channel (Δ) is connected to the input of a third mixer (13), the other input of which is connected to the second intermediate frequency oscillator (F2), to allow detection of the signal (∑'r) received on the sum channel (∑) relative to the intermediate frequency signals (Fj, F2), and detecting the signal (Δ'r) received on the difference channel (Δ) with respect to any of the intermediate frequency signals (F2).

7. Device according to claim 6, characterized in that the signals from the mixers (11, 12, 13) being sampled and coded by analog-digital converters (17, 18, 19), Doppler filters (20) are connected at the output of these converters.

8. Device according to claim 7, characterized in that detection means (21) connected at the output of the Doppler filters (20) make it possible to detect the presence of a number P of targets by relative comparison and with respect to a threshold, the output power of the different Doppler filters.

9. Device according to claim 8, characterized in that processing means (22) connected at the output of the detection means (21) make it possible to estimate the speed, the distance and the angular position of each of the P targets.

10. Device according to claim 9, characterized in that the processing means transmit through an interface (23), the distance, position and speed information relating to the target deemed most dangerous to a decision-making body.