DE102006032487A1 - Radar sensor with several transmit and receive channels - Google Patents

Abstract

Radar sensor comprising a plurality of channels (1, 2, 3, 4, 10, 12) fed from a common RF source (18) for transmitting and receiving RF signals, characterized in that at least one of the channels (2, 3, 4 ; 12) transmitter side has a modulator (22; 52) which modulates the signal supplied by the RF source (18) in a specific manner for the channel in question.

Description

State of the art

The The invention relates to a radar sensor having a plurality of common RF source fed channels for transmitting and receiving RF signals.

Such Radar sensors are used for example in so-called ACC systems (Adaptive Cruise Control) for Used motor vehicles and then serve the distances and To measure relative speeds of preceding vehicles, so that one Adaptive distance and speed control is enabled.

at the multiple channels For example, they can be directional channels, each with a or several antenna elements are associated, which are in their Main emission direction and / or main sensitivity direction of Channel to channel differ, so that an angle-resolving Radarortung allows becomes. This allows, for example, between preceding vehicles on to distinguish one's own lane and vehicles on secondary lanes.

at The antenna elements may be, for example, individual antennas or patches that offset one another with respect to the optical axis common radar lens are arranged. The directional characteristic each antenna element, especially the direction of the greatest radiation intensity or the greatest sensitivity, is then offset by the displacement of the element in question given optical axis. Optionally, it can be at the antenna elements but also so-called phased arrays of several sub-elements act, which transmit signals are supplied with such a phase relationship, that yourself through interference the desired Directivity results. For sending and receiving the radar signals can the same Antenna elements or optionally also separate antenna elements to be used.

As an example of an angle-resolving radar sensor describes EP † 1 380 854 A2 a static FMCW multibeam radar. The term "static" in this context means that the directions of the radar beams generated by the individual antenna elements are fixed in time, so that the entire detection angle range of the angle-resolving radar sensor can be monitored simultaneously by parallel evaluation of the signals supplied by the individual antenna elements.

at An FMCW (Frequency Modulated Continuous Wave) radar is the frequency the output signals supplied to the individual antenna elements ramp-modulated. The signal received by each individual antenna element is sent to the Mixed transmission signal that is supplied to this antenna element. In this way receives one an intermediate frequency signal whose frequency is the frequency difference between the transmitted signal and the received signal. This frequency difference is due to the Doppler effect of the relative speed of the located object is dependent However, due to the modulation of the transmitted signal from the Signal delay and thus dependent on the distance of the object.

The Intermediate frequency signals are digitized and transmitted via a Time span, which corresponds approximately to a single frequency ramp recorded. Of the The signal curve thus obtained is then transformed by Fast Fourier Transformation decomposed into its frequency spectrum. Everybody excels in this spectrum located object by a single peak whose frequency position the distance and the relative speed of the object in question dependent is. When the transmitted signals alternate with frequency ramps be modulated with different ramp slopes, for example with a rising and a falling ramp, so can be for a single Object from the position of the peaks in the spectra obtained for the two ramps the distance and the relative speed of the object clearly determine. If several objects are located simultaneously, so is for a clear assignment of the peaks to the respective objects Modulation of the transmitted signals with at least one other Frequency ramp required.

For each Channel receives on each frequency ramp, a spectrum in which the located objects are located in the form of a peak. For to a single object belonging Peaks is the amplitude and phase of the intermediate frequency signal, for example at the apex of the peak, slightly different from channel to channel. The differences in amplitude and phase, in summary, too referred to as complex amplitude, result from the different Directional characteristics of the antenna elements and are of the azimuth angle of the object in question.

For each individual antenna element, the complex amplitude shows a characteristic dependence on the azimuth angle, which can be represented in an antenna diagram. The distance and the relative velocity of the object enter the complex amplitude only in the form of a phase factor which is the same for all channels. By comparing the complex amplitudes in the different channels, therefore, the azimuth angle of the object in question can be determined. In simple words For this purpose, the azimuth angle is sought, in which the complex amplitudes measured in each case at the apex of the peak best fit the associated antenna diagrams.

at the well-known radar sensor is all Antennenelmenten the same frequency modulated transmit signal supplied. When Example can be assumed that for sending and for receiving the same antenna elements are used (monostatic antenna concept). Each antenna element receives then a radar echo not only from the signal it sent itself, but also from those sent by the other antenna elements Signals. All these signals have, provided they are from the same object come, the same frequency and overlay at the receiving antenna element to a sum signal. there It may be due to interference in certain object constellations a widespread extinction of the signal come in one channel, so that the accuracy and reliability the Radarortung impaired becomes.

at other known radar sensors serve the different channels, the location for optimize long, medium and short ranges. For example For example, a channel can function as a long-range sensor whose antenna element or elements produce a relatively sharply focused radar lobe, while in a different channel a fanned radar lobe is generated, in the near Advance of the vehicle a larger range of angle capture. The antenna elements differ in this case primarily in their areal Extension and thus in their numerical aperture.

Also in radar sensors of this type, it may be due to interference effects an unwanted signal suppression or -auslöschung come. Particularly problematic here is that there is a risk that in one Channel with relatively lower signal strength the received signal is outshone by a signal from another channel and is therefore no longer detectable.

A possible solution This problem is that the different channels are time multiplexed be operated, so that too only one channel transmits and receives at any one time. at Radar sensors for However, motor vehicles this has the disadvantage that the traffic only with correspondingly lower temporal resolution can be tracked.

Disclosure of the invention

task The invention is therefore a radar sensor with several simultaneously active channels to create, at the unwanted Avoiding interference effects between the different channels become.

These Task is in a radar sensor of the type mentioned by solved, that at least one of the channels Transmitter side has a modulator, that of the RF source delivered signal in a for modulates the respective channel specific way.

Thereby, that this transmitted signal is modulated in each channel in a specific way is, by frequency modulation, amplitude modulation and / or phase modulation, the signals are at the receiving end based on their channel-specific modulation distinguishable from each other, so that the undesired interference and blooming effects are suppressed.

advantageous Embodiments and further developments are specified in the subclaims.

Around in a radar sensor with three or more channels a complete channel separation To reach all channels should be have a channel-specific modulation except for one. there it is useful if the received signals by the modulation in a frequency band be moved with the appropriate frequency bands for the others channels not or as possible little overlapped. In the evaluation of the received signal or derived therefrom Intermediate frequency signals will then only for the respective Considered channel relevant frequency band, and the evaluation system is then for the signals from other channels blind, because these signals are in other frequency bands.

at FMCW radar, the channel-specific modulation comes to the ramp-shaped modulation which can already be done in the RF source and thus for all channels the same is.

If the signals are shifted to higher frequencies by the channel-specific modulation, then the following advantageous side effect can optionally be exploited:
The position of the signal generated by a radar object in the frequency spectrum is, as explained above, dependent on the relative speed of the object and therefore at certain relative speeds in the so-called DC region of the spectrum, ie in the frequency range in the vicinity of the frequency zero , be shifted or even in the range of negative frequencies. Signal components in the DC range can not be detected or evaluated with conventional FMCW radar sensors. Positive and negative frequencies differ in the complex intermediate frequency signal Z = | A | e ^ift by the sign of the frequency f. However, since in the conventional FMCW method ultimately only the absolute value of the real part of the intermediate frequency signal is evaluated, no distinction can be made between positive and negative frequencies, so that falsification of the measurement result can occur if significant signal components lie in the negative spectral range. The inventive modulation and frequency shift can now be achieved that the entire signal or at least a greater proportion of the same is in the evaluable positive frequency range.

On the other hand, it is also possible again to demodulate the received signals channel specific and so in the original Transform back the frequency band. The evaluation can then be done in all channels in the same frequency band respectively. The channel separation is retained, because only for its own Channel is the demodulation inverse to the transmitter-side modulation. Non-channel signals therefore become demodulated by others frequency bands postponed.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 a block diagram of a radar sensor according to an embodiment of the invention;

2 a sketch for explaining the operation of the radar sensor according to 1 ;

3 an antenna diagram for a channel of the radar sensor after 1 ;

4 a frequency / time diagram for modulated signals appearing in different channels of the radar sensor 1 to be sent;

5 a spectrum of a radar signal received in one of the channels;

6 a sketch illustrating the construction of an angle-resolving radar sensor according to another embodiment of the invention; and

7 a circuit diagram for the radar sensor after 6 ,

In 1 is a block diagram of an FMCW radar sensor with two simultaneously activatable channels 10 and 12 shown. In the example shown, a bistatic antenna concept is realized, ie, each of the two channels 10 . 12 is ever a transmitting antenna 14 and a separate receiving antenna 16 assigned.

The transmitting antenna 14 of the canal 10 is provided by a local oscillator serving as an RF source 18 supplied a ramp-shaped high-frequency signal whose frequency is of the order of 76 GHz. That from the transmitting antenna 14 transmitted signal is after reflection from a radar target, not shown, from the receiving antenna 16 received this channel and a mixer 20 fed. There, the received signal is received by the oscillator 18 supplied signal, and thus an intermediate frequency signal Z1 is generated, whose frequency corresponds to the frequency difference between the transmitted signal and the received signal. The intermediate frequency signal Z1 is then evaluated in an evaluation circuit, not shown here in the usual way for FMCW radar systems.

The channel 12 has a similar structure as the channel 10 but here is between the local oscillator 18 and the transmitting antenna 12 a modulator 22 inserted, which is the signal of the oscillator 18 with one of a local oscillator 24 modulated modulation signal modulated. This will be the transmission antenna 14 in the canal 12 radiated signal shifted to a higher frequency band.

In the example shown is also in the channel 12 between the receiving antenna 16 and the mixer 20 a demodulator 26 inserted, which also from the auxiliary oscillator 24 obtained modulating signal and which performs on the signal received by the antenna to the modulation of the modulator inverse demodulation before the signal in the mixer 20 with the signal of the oscillator 20 is mixed and so an intermediate frequency signal Z2 is generated.

The operation of the radar sensor described above will now be based on the 2 to 5 be explained in more detail.

In 2 are symbolic of the two channels 10 and 12 belonging transmit antennas shown here for better distinction with 14-10 and 14-12 are designated. Both antennas are as well as the associated receiving antennas 16 (in 2 not shown) in the focal plane of a microwave lens 28 which focuses the emitted radar radiation and focuses the received radiation back onto the receiving antenna.

The transmitting antenna 14-10 is extensively extended and therefore produces a relatively sharply focused radar lobe 30-10 for locating objects that are within a relatively narrow angular range, but at a relatively large distance. The transmitting antenna 14-12 has a smaller extension and produces a further fanned radar lobe 30-12 with which objects located within a larger angular range can be located in the lower distance range. For example, if the radar sensor is mounted on the front of a motor vehicle and directed forward, then the radar lobe may be used 30-10 preceding vehicles, especially those in their own lane, are located while using the radar lobe 30-12 also the edge development, z. As crash barriers, parking vehicles on the roadside and the like can be located.

In the 2 not shown receiving antennas 16 are analogous to the transmitting antennas 14 dimensioned and arranged. For example, the various antennas in the plane of the drawing in 2 vertical direction offset from each other in front of the common microwave lens 28 be arranged. Due to the different extent of the antennas, it is also conceivable that, for example, the transmitting antenna 14-12 nested in the then consisting of several elements transmit antenna 14-10 is arranged.

In 2 is still an object 32 shown in the overlap area of both radar lobes 30-10 and 30-12 located and thus located in both channels of the radar sensor.

3 shows an antenna diagram for the channel 12 who is responsible for locating at close range. The curve drawn as a solid line 34 indicates the amplitude of the radar echo received by an object as a function of the azimuth angle j of the object. According to the far fanned out form of the radar club 30-12 this curve has a relatively flat maximum at the azimuth angle 0, and it falls approximately symmetrically on both sides, with relatively weak side lobes, relatively gently, so that even at higher azimuth angles still a high sensitivity is achieved.

The receiving antenna 16 for the channel 12 However, not only does this receive from the transmitting antenna 14-12 sent and to the object 32 reflected signal, but also the reflected signal from the transmitting antenna belonging to the other channel 14-10 was sent. If that from the transmitting antenna 14-12 not sent signal with the help of the modulator 22 would be modulated, the signals received from both channels would have the same frequency, so that they would interfere between them, as in FIG 3 schematically by the dashed line curve 36 is pictured. It can be seen that under these circumstances, at certain azimuth angles, in the example shown approximately at j = ± 18 °, an extensive signal extinction would occur. An object that was at one of these azimuth angles could thus be in the channel 12 can not be located, because the radar echo would be so weak that it would no longer be discernible from the background noise. The from the two channels 10 and 12 The information obtained would therefore be inconsistent, which would considerably complicate the evaluation of the traffic situation and could easily lead to misinterpretations.

Corresponding disruptive effects were of course also in the channel 10 occur because its receiving antenna and that of the transmitting antenna 14-12 receives received signal and it would also be due to the Frequenzgleicheit between these signals to interference. An extensive extinction of a signal in this channel could then lead to the misjudgment that this only in the channel 12 located object outside the radar club 30-10 (on the roadside) and thus is not a relevant obstacle.

By modulating the in the channel 12 transmitted signal, interference and errors of this type are effectively avoided.

In 4 are those of the transmitting antennas 14 Both signals transmitted in a frequency / time diagram shown. The curve 38-10 gives the frequency response of the channel 10 signal transmitted with that of the local oscillator 18 supplied signal is identical. It can be seen that the frequency is modulated in a ramp, with an alternating sequence of rising and falling ramps with the magnitude of the same slope. The curve 38-12 is that in the channel 12 sent signal. This signal has the same ramped modulation as that of the oscillator 18 is derived, however, in addition due to the effect of the modulator 22 shifted in its frequency. This frequency shift Df is so large that the frequency band in which the frequency of the channel 12 transmitted signal does not vary with the corresponding frequency band for the channel 10 overlaps.

In 5 is for the in 2 shown object constellation, the spectrum of the intermediate frequency signal Z2 shown in the channel 12 receives. Because the object 32 from both radar beams 30-10 and 30-12 is taken and the receiving antenna 16 of the canal 12 receives the reflected signals from both transmit antennas 14-10 and 14-12 have been sent, the object must be 32 in the spectrum by two peaks. Due to the modulation in the channel 12 these peaks are shifted by Df.

The dashed curve 40 in 5 indicates the spectrum in case the channel 10 would be switched off, so only that of the transmitting antenna 14-12 sent signal received. This spectrum has a peak at a frequency f1, which is determined by the distance and the relative speed of the object 32 is determined. Although it was through the modulator 22 the frequency of the transmitted signal increases by Df, but this frequency increase is by the demodulator 26 undone so that the frequency of the intermediate frequency signal Z2 only from the difference between the frequency of the received signal and the frequency of the local oscillator 18 is dependent.

In the 5 as a thin continuous line drawn curve 42 Specifies the spectrum that would be obtained if only the signal from the transmitting antenna 14-10 in the canal 10 would receive. This signal has not been modulated on the transmitter side, but will nevertheless, if it is in the channel 12 is received by the demodulator 26 demodulated and thereby reduced in frequency by Df. Consequently, the corresponding peak in the spectrum is now at a frequency f2, outside the range F of the spectrum used for the signal evaluation.

In fact, in the channel 12 receive the sum signal that is in 5 through the bold curve 44 is represented and a superposition of the curves 42 and 40 equivalent. However, since the signal portion of the channel 10 originates (curve 42 ) in the evaluable range F of the spectrum is practically 0, the curve is 44 in this evaluable range almost with the curve 40 identical, that is, the signal received and used for the evaluation by the same time from the other channel 10 received signal is not distorted or covered, although in the example shown, the signal strength in the channel 10 higher than in the channel 12 ,

It understands that the above explained principle applicable analogously to radar sensors with three or more channels, with which three or more radar beams are generated, which are connected to one Area big Distances, a range of mean distances or a range of small distances customized are.

6 shows an example of a four-channel angle-resolving monostatic radar sensor. The channels are here with 1 . 2 . 3 and 4 and by mutually angularly offset radar beams 46 symbolizes. Each radar beam is from an antenna 48 , For example, generates a patch antenna, which serves both for sending and for receiving. The antennas 48 are offset from the optical axis of the microwave lens 28 arranged so that the radar beams 46 be radiated in slightly different directions.

7 shows a circuit diagram for the radar sensor according to 6 , As in the previously described embodiment, the local oscillator generates 18 a ramped modulated high frequency signal, the - possibly after modulation - the antennas 48 is supplied. In the channel 1 becomes the signal of the oscillator 18 remodulated via a circulator 50 into the antenna 48 fed. The circulator 50 serves in a known manner to the transmitted signal from that via the antenna 48 disconnected signal, so that only the received signal to the mixer 20 for generating the intermediate frequency signal passes.

In the channels 2 . 3 , and 4 is in each case in the line, by the oscillator 18 to the circulator 50 leads, a diode 52 arranged, which serves as a modulator. Specifically, here is the bias of the diode 52 with the help of a local oscillator 54 modulated. series capacitors 56 in front of and behind the diode 52 make sure that the bias current only from the local oscillator 54 to a NF mass 58 flows while the RF signal without NF component to the circulator 50 arrives.

In the direction of the circulator 50 to the mixer 20 is in each of the channels 2 . 3 and 4 a diode serving as a demodulator 60 arranged. Associated series capacities and a MF ground are, according to the polarity of the diode 60 in the same way as the diode 52 arranged. Within each channel, the bias becomes for the diodes 52 and 60 from the same local oscillator 54 generated so that the demodulation corresponds exactly to the modulation in the respective channel.

The auxiliary oscillators 54 that the channels 2 . 3 and 4 are assigned, but have different frequencies from each other, so that the modulation and demodulation is each channel-specific.

The through the diode 52 Modulation caused by nature is predominantly an amplitude modulation by nature, which, however, leads to sidebands in the frequency spectrum. By skillful tuning of the components can be achieved that the majority of the oscillator energy flows in the first sideband, so that the antenna 48 , for example in the canal 2 , a relatively strong RF signal can be supplied, which is opposite to the frequency of the local oscillator 18 is shifted by a channel-specific amount Df.

Claims (8)

Radar sensor with several from a common RF source ( 18 ) fed channels ( 1 . 2 . 3 . 4 ; 10 . 12 ) for transmitting and receiving RF signals, characterized in that at least one the channels ( 2 . 3 . 4 ; 12 ) transmitter side a modulator ( 22 ; 52 ), that of the RF source ( 18 ) is modulated in a manner specific to that channel. Radar sensor according to claim 1, characterized in that that he n-channels has, with n ≥ 3, and that n † - 1 channels channel specific are modulated. Radar sensor according to claim 1 or 2, characterized in that each channel ( 2 . 3 . 4 ; 12 ), which is a modulator ( 22 ; 52 ), a demodulator at the receiving end ( 26 ; 60 ) which performs modulation inverse demodulation on the received signal. Radar sensor according to one of the preceding claims, characterized in that the modulators ( 22 ; 52 ) are adapted to adjust the frequency of the RF source ( 18 ) to move in different from channel to channel Frequnenzbänder. Radar sensor according to claim 4, characterized in that that the frequency bands do not overlap each other. Radar sensor according to one of the preceding claims, characterized characterized in that is designed as FMCW radar and that in the various channels sent signals in addition to the channel-specific modulation a common ramp-shaped modulation exhibit. Radar sensor according to one of the preceding claims, characterized in that the different channels ( 10 . 12 ) various transmitting and / or receiving antennas ( 14 . 16 ), the differently concentrated beams ( 30-10 . 30-12 ) produce. Radar sensor according to one of Claims 1 to 6, characterized in that the different channels ( 1 . 2 . 3 . 4 ) various transmitting and / or receiving antennas ( 48 ) associated with each other angularly offset radar beams ( 46 ) produce.