DE102004034429A1 - Vehicle radar front end for detecting long, medium and short distances, has sequential-transmission antennas between two reception antennas supplying parallel signals to control and processing unit - Google Patents

Abstract

The radar signal source (15) is connected to transmitting elements (1), e.g. horn antennas, via a switching matrix (3). This supplies them (1) sequentially with a transmission signal. There are at least two reception elements (2) e.g. horn antennas, with spatially-intervening transmission elements (1). A digital control and processing unit (20) is provided for signals received, which are supplied to it (20) in parallel.

Description

The The present invention relates to a radar front-end and more particularly a radar front-end for automotive applications, that for both the detection of short as well as medium and / or long distances suitable is.

Out In the prior art are arrangements of 4 to 6 on the entire vehicle width (eg in the bumper) distributed one-dimensionally measuring single sensors known as u. a. from KLOTZ, Michael in "An Automotive Short Range High Resolution Pulsed Radar Network ", Shaker Verlag, Aachen, 2002, WENGER, J .; SCHNEIDER, R. in "Automotive Radar Sensors ", IEEE MTT-S Int. Microwave Symposium (IMS), Automotive Radar Workshop, 2002, or GRESHAM, I .; JENKINS, A .; EGRI, R .; ESWARAPPA, C .; Kolak, F .; WOHLERT, R .; BENNETT, J .; LANTERI, J-P. in "Ultra Wide Band 24GHz Automotive Radar Front-end ", in IEEE MTT-S Int. Microwave Symposium (IMS) Digest Vol. 1, 2003, pp. 369-372 described.

The Two-dimensional mapping is based on the principle of multilateration from the distance measurements of all existing individual sensors and they provides relatively good imaging properties at distances in of the order of magnitude the sensor distance.

The above solution However, it is disadvantageous in that the angular resolution with the distance decreases and ambiguities in complex target scenarios arise. About that In addition, a lot of effort goes with the installation of numerous sensors and their networking. The installation positions must be on be known exactly a few millimeters. Because angle and distance resolution off the available bandwidth are compromised on bandwidth needs and resolution necessary.

Another known from the prior art method is the difference lobe method. The angular resolution is achieved by comparative evaluation of the radar echoes received by antennas with different radiation patterns. Differential lobe methods are already being used in automotive radar sensors such as OHSHIMA, S .; ASANO, Y .; HARADA, T .; YAMADA, N .; USHUI, M .; HAYASHI, H .; WATANABE, T .; IIZUKA, H. in "Phase Comparison Monopulse Radar with Switched Transmission Beams for Automotive Applications", IEEE MTT-S Int. Microwave Symposium (IMS) Digest Vol. 4, 1999, pp. 1493-1496, by ASANO, Y .; OHSHIMA, S. in US 6,246,359 B1 , or HARTZSTEIN, C. described in "76 GHz Radar Sensor for Second Generation ACC" ATA Vol. 55, 2002, pp. 408-416. In particular, describes US 6,246,359 B1 a radar device comprising a plurality of sequentially connected transmitting antennas each having differently directed beams, two receiving antennas arranged side by side and offset from the transmitting antennas for receiving the reflected transmitting signals, and an azimuthal direction detecting device due to the phase difference between the received ones reflected transmission signals.

The The differential lobe method described above provides fast an image in parallel processing, with beamforming to optimal illumination of a defined field of view required is, and thus has a big one Range through highly concentrated Antenna lobes.

The However, differential lobe method also has disadvantages such. B. the big one Space required for Antennas and feed networks or the high precision requirements of the Antenna realization for achieving defined radiation lobes. About that In addition, changes can be made the antenna diagrams (squint, side lobes) by pollution and temperature effects arise and changes in the installation environment to lead to aberrations. The angular resolution of objects in the same Removal cell is not possible.

Additionally, from ASANO, Y .; HARADA, T. in US 6,288,672 B1 and ASANO, Y. in "Millimeter-Wave Holographic Radar for Automotive Applications", European Microwave Conference (EuMC), 2001, describes a holographic radar apparatus comprising a plurality of transmitting antennas, which are also switched sequentially, and at least two juxtaposed ones Receiving antennas, which receive the reflected waves according to a time-division multiplex method, wherein the distance of the transmitting antennas is determined in dependence on the number of receiving antennas.

moreover is the focus of the prior art described above in the imaging process and the problems of realizing Radar front-ends are not addressed.

Therefore it is an object of the present invention an improved Radar front-end available to provide a good mapping functionality in conjunction with a relative realized low hardware cost.

Within the scope of the above problem, a Ra A front-end is provided which maps the area in front of a vehicle in particular over a few vehicle widths and up to an average distance (of eg at least 30 m) by means of radar so well that all conceivable road users and obstacles clearly even in complex scenarios can be recognized as targets and localized in two dimensions with good resolution.

A Another particular object of the present invention is in the provision of a radar front-end that has a good mapping functionality as possible low hardware costs electronically especially without realized mechanically moving antennas.

A additional Object of the present invention is to provide a radar front-end that recognizes moving targets and in terms of evaluated their relative speed to the sensor.

Summary the invention

These and further to be taken from the following description tasks are solved by a radar front-end according to claim 1. Further advantageous embodiments of the invention are set forth in the dependent claims.

Further Features and advantages of the present invention as well as the structure and the operation of various embodiments of the present invention The invention will be described below with reference to the accompanying drawings described. The accompanying drawings illustrate the present invention Invention and, together with the description, further serve the principles to explain the invention and to enable a person skilled in the field to to manufacture and use the invention. Showing:

1 a block diagram of the basic structure of the radar front-end according to the present invention;

2A a block diagram of a first embodiment of a signal source in the radar front-end of 1 can be used;

2 B a block diagram of a second embodiment of a signal source in the radar front-end of 1 can be used;

3 a block diagram of the basic structure of the radar front-end according to the present invention, which is extended by a remote receiver assembly with a receiving element;

4 a block diagram of a radar front-end according to the present invention with a first embodiment of a heterodyne receiving structure;

5 a block diagram of a radar front-end according to the present invention with a second embodiment of a heterodyne receiving structure; and

6 an extension of the radar front-end of the invention 4 on complex reception channels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION With reference to FIGS 1 For example, the solution of the present invention is based on a basic structure having a plurality of horizontally equidistantly equal transmission elements used for transmission 1 connected to the outputs of an electronic switching matrix 3 are operatively connected, which is formed, the transmitting elements 1 to supply sequentially with a transmission signal. On both sides next to the transmitting elements 1 are two receiving elements 2 , as can be seen not with the switching matrix 3 are connected. According to a presently preferred embodiment, at least sixteen (16) transmit elements 1 provided that the person skilled in the art understands that their number depending on z. B. will vary from the desired azimuthal resolution. Furthermore, the receiving elements 2 , like in the 1 visible, at the same distance from the respective adjacent transmitting element 1 to be ordered.

To In an advantageous aspect of the present invention, the distance the antenna elements (i.e., the transmitting and receiving elements) for avoidance secondary Nebenmaxima in the synthetic radar image to a maximum of half the free space wavelength of Operation frequency (≤λo / 2) of the Radar front-ends limited.

Further It is preferred that all antenna elements have the same radiation pattern with as possible wide opening angle in the horizontal, so that the entire horizontal field of view of each individual element is covered. In the vertical is preferred that the antenna patterns of the antenna elements one with the vertical Have sensor dimensions realizable bundling.

The two next to the transmitting elements 1 arranged receiving elements 2 can be used for medium and long distances and storage angles within ≤ ± 45 ° to increase the angular resolution according to, for example, KEES, N .; SCHMIDHAMMER, E .; DETLFFSEN, J. in "Improvement of Angu See, for example, US Pat. No. 5,415,774, which is incorporated herein by reference in its entirety by reference to the present invention, which is incorporated by reference herein in its entirety Storage angles and short distances serve the receiving elements 2 whose distance at the largest bandwidth of the radar front-end should be greater than a range cell, to resolve ambiguities in the radar images.

Like in the 1 has shown switching only the transmitting elements 1 and not the receiving elements 2 the advantage that the reception noise figure is not due to the attenuation of the switching matrix 3 is worsened. Because the damping of the switching matrix 3 transmission side simply by increasing the output power of a transmission amplifier 10 until the allowable EIRP (Equivalent Isotropic Radiated Power) is reached, with which transmission power one would have to supply an isotropically radiating antenna in all spatial directions in order to achieve the same power flux density in the far field as with a focusing directional antenna in its main transmitter direction) can, are moderate losses of the switching matrix 3 acceptable and thus cost-effective realizations possible.

Furthermore, with reference to the 1 can be the outputs of the receiving elements 2 optionally via a corresponding low-noise preamplifier 4 with the inputs of receiving mixers 5 be connected, each with the outputs of the receiving elements 2 are coupled. About the switching matrix 3 For example, a frequency-modulated transmission signal is sequentially inputted to each of the transmission antennas 1 fed. Signals reflected by targets (not shown) pass in parallel through the two receiving elements 2 received and with a part of the transmission signal, which is via the respective receiving mixer 5 homodyne is converted into the baseband. The baseband signals are in a respective one with a corresponding receive mixer 5 associated baseband level 6 amplified, with a low pass of the baseband stage 6 filtered and then for the following computational processing in a with reference numerals 20 designated block for the digital control and processing of the received signals (hereinafter also referred to as DSV) in each case with the low-pass of the baseband stage 6 connected analog-to-digital converter 7 digitized.

Resolution in the distance direction may be at the radar front-end of the 1 be generated according to the principle of the frequency-modulated continuous wave radar (FM-CW radar). Transverse resolution can be obtained from the relative phases of successive different combinations of transmit and receive elements 1 . 2 received received signals are obtained. So that two-dimensional radar images can be calculated from the signals recorded for many frequencies (frequency modulation) and many combinations of elements, all received signals must be evaluable in terms of magnitude and phase (coherently) with respect to a reference signal. This can be realized according to the invention in that a voltage-controlled microwave oscillator 8th via a synthesizer 9 to a high-precision low-frequency quartz oscillator 11 coupled, which together form a coherent signal source 15 form, wherein the frequency modulation of the transmission signals is generated digitally. Two advantageous embodiments of the invention for this purpose applicable synthesis architecture of the coherent signal source 15 will be referred to in the following 2A and 2 B executed. A useful frequency range of the radar front-end results from the application areas and is for example in the micro or millimeter wave range (20 GHz - 100 GHz).

The digital signal processing of the outputs of the respective analog-to-digital converters 7 , which correspond to the received signals, takes place in the DSV 20 , which can be designed as a process computer. Below are only the functional processes in the DSV 20 explained by coarse function blocks, since the details whose implementation is familiar to those skilled need no further clarification. In particular, the DSV includes 20 a flow control 21 for the recording sequence and the processing of the received by the radar front-end receiving signals and processing units 22 for the calculation of the distance and a processing unit 23 for the calculation of the transverse direction.

For controlling the recording sequence, the synthesizer may be preferred 9 , the switching matrix 3 and the analog-to-digital converters 7 the two receiving channels (or the two received signals) of the radar front-end by the flow control 21 be addressed. The received data obtained in a recording sequence becomes a two-dimensional radar image by computational processing 24 won. The computational processing can, as in the 1 exemplified, sequentially in the direction of removal (in the processing units 22 ) and transverse direction (in the processing unit 23 ) be performed.

In the 2A respectively. 2 B Two options are presented for realizing the frequency-modulated coherent signal source required for the operation of the radar front-end.

In the embodiment of the 2A in which the coherent signal source is denoted by the reference numeral 15A is a frequency-modulated low-frequency signal of high modulation linearity and coherence by a direct digital synthesizer 17 from a fixed-frequency, highly stable quartz oscillator 11 and to the reference frequency input of a phase locked loop 16 with frequency divider (1 / N), reference divider (1 / R) and phase frequency detector (PFD) given. The phase locked loop sets the low frequency signal corresponding to the fixed integer divisor factors P and N to the desired output frequency of the voltage controlled oscillator 8th in the right order.

In the embodiment of the 2 B in which the coherent signal source is denoted by the reference numeral 15B is called a fractional-n phase locked loop 18 used. The frequency divider of this phase locked loop 18 can also be set to non-integer values. This allows frequency-modulated signals directly from a fixed-frequency quartz oscillator 11 at a PLL reference input of the phase locked loop 18 by generating the frequency divider value n. The variation of the frequency divider value is from a likewise by the quartz oscillator 11 synchronized digital generator 19 controlled according to the given modulation.

The above two embodiments of implementing coherent frequency-modulated signal sources and other signal sources not discussed here are known in the prior art (see, for example, MUSCH, T .; SCHIEK, B. "A High Precision Analog Frequency-Ramp Generator Using a Phase Locked-Loop Structure in the European Microwave Conference (EUMC) Conferenee Proceedings, 1997, pp. 62-68; MUSCH, T .; SCHULTE, B .; SCHIEK, B. "A Fast Heterodyne Network Analyzer Based on Precision Linear Frequency Ramps in European Microwave Conference (EUMC) Conference Proceedings, 2001; METZ, C .; GRUBERT, J .; HEYEN, J .; JACOB, AF; JANOT, S., LISSEL, E .; OBERSCHMIDT, G., STANGE, LC "Fully integrated automotive radar sensor with versatile resolution" in IEEE Transactions on Microwave Theory and Techniques 49 (2001), December, No. 12, pp. 2560-2566; MAYER, W .; WETZEL, M., MENZEL, W "A novel directimaging radar sensor with frequency scanned antenna "in IEEE MTT-S International Microwave Symposium (IMS) Digest Vol 003, pp. 1941-1944; MAYER, W .; MILK, M .; GRABHERR, W .; NÜCHTER, P .; GÜHL, R. "Eight-Channel 77 GHz Front-End Module With High-Performance Synthesized Signal Generator for FM-CW Sensor Applications" IEEE Transactions to Microwave Theory and Techniques 52 (2004), March, No. 3, and DE 198 13 604 A1 ). In accordance with the presently intended embodiments of the invention, the above signal sources are preferred in terms of performance and cost.

Improved imaging at very small distances and large horizontal shelves can be achieved with the circuit of 3 be achieved. This improvement is relevant in particular for the field of application of the parking aid and can be achieved according to the invention in that the sensor architecture is provided with a remote receiving element mounted at a certain distance D from the basic structure 31 is extended and so the benefits of triangulation in the special angle and distance range of the parking function can be shared.

Like from the 3 As can be seen, the radar front-end is based on the embodiment of FIG 1 in which the signal source of the 2A is implemented. Therefore, the same reference numerals are used to designate the same elements of the above-mentioned figures and their explanation is omitted. However, it is also conceivable, the embodiment of 3 with the signal source of 2 B to implement.

A remote receiver module 30 includes a receiving element 31 , an optional low-noise preamplifier 32 , a reception mixer 33 , a baseband level 34 and one via a phase locked loop 35 controlled microwave oscillator 36 , The connection of the remote receiver module 30 according to the radar front-end architecture according to 1 with the realization of the coherent signal source according to 2A only needs two low-frequency signal lines 39 and is therefore easy and inexpensive to implement. For digitizing the output signal of the remote receiver module 30 becomes the basic structure around another analog-to-digital converter 37 complemented, the output signals then together with the signals from the two existing receiving elements 1 and 2 the DSV 20 to provide. The evaluation of these signals is then carried out in a manner known to those skilled in the art and will not be further explained herein.

According to another aspect of the present invention, an improvement in the target dynamic range of a radar front-end can be achieved, as described below with reference to FIGS 4 and 5 explained.

In conjunction with the embodiment 1 described receiving arrangement of FM-CW radar is constructed homodyne. In this case, the received signal with the receiving mixer, whose oscillator signal corresponds to the transmission signal, converted directly into the baseband. The disadvantage of homodyne receive arrangements, however, is the increased noise figure at low baseband frequencies due to phase and amplitude noise of the local oscillator. Both noise contributions take over the frequency but limit the maximum target dynamic range in typical FM-CW short-range radar sensors. While the contribution of phase noise to noise figure at short target ranges, such as. As in a parking aid, automatic storage and a precrash, is reduced by the correlation effect of the receiving mixer, the amplitude noise is formed directly in the target spectrum and thus in the radar measurement. This is particularly the case if the radar front-end architecture is to fulfill all the tasks of forward-looking automotive sensors and at the same time be used wherever two-dimensional radar images of complex scenarios are to be recorded over a large range of vision close to the sensor.

In Realistic traffic scenarios are very large target dynamic ranges expected. So can z. B. the Rückstreuquerschnitte of a motor vehicle and a pedestrian by a factor of 100. Amplitude noise in the receiver often has its cause in the parasitic coupling of the transmitting or local oscillator signal in the receive path. By the close Stringing of transmitting and receiving elements and the necessary compact structure, this problem is described in the here To expect architecture.

To solve this problem, according to the invention, respective heterodyne variants of the radar front-end can be provided with improved properties with regard to the contribution of the amplitude noise, and thus a higher target dynamic range, as in FIGS 4 and 5 explained.

In particular, in the 4 a first embodiment of a heterodyne architecture with separate synthesizers for transmit and local oscillator signals, wherein separate synthesizers for transmit signal and local oscillator signal are provided. In particular, analogous to the embodiment of the 1 the synthesizer 9 provided for generating the transmission signal (SS in the 4 ) and another synthesizer 41 for generating the local oscillator signal (SLO in the 4 ). In the 4 the same reference numerals are used to designate the same elements of the 1 used and their explanation is omitted.

The transmit signal and the local oscillator signal can be generated with the same frequency modulation but different absolute frequency. The reception mixer 5 are respectively adapted to mix the received signals with the local oscillator signal and to obtain a target signal which then does not map to the baseband but as a bandpass signal to an intermediate frequency corresponding to the difference of the absolute frequencies set for the transmit signal and the local oscillator signal. The freely adjustable by the synthesizer architectures frequency difference _(fdiff) between the transmission signal and the local oscillator signal is now chosen so high that it is well above the frequency range of the amplitude noise disturbed baseband. That at the outputs of the receiving mixer 5 obtained bandpass signal is in an intermediate frequency stage 45 filtered and amplified and then only with another mixer 46 converted to baseband for further sampling. The frequency of the local oscillator of the further mixing stage 46 corresponds to the center frequency of the bandpass signal _fdiff . Due to the previous amplification of the bandpass signal, the noise contributions of the further mixer stage 46 negligible compared to the signal level and thus eliminated. To preserve the coherence, the local oscillator signal of the further mixer stage must also be present 46 with the quartz oscillator used as a reference 11 be synchronized. This could be z. B. by another synthesizer (not shown). However, the difference _{frequency fdiff becomes} an integer part of the frequency of the quartz oscillator 11 set, so the local oscillator signal can easily with a divider block 44 will be realized. This realization is characterized not only by low effort, but also by minimal noise contributions.

In the 5 A second embodiment of a heterodyne architecture with a single synthesizer is shown. In the 5 are also the same reference numerals to designate the same elements of 1 used and their explanation is omitted.

In the micro and millimeter wave range signals are often generated at lower frequencies and converted by integer frequency multiplication in the desired frequency range. 5 shows how in such cases a heterodyne architecture with only one synthesizer and thus less hardware than in the embodiment of the 4 can be built. The frequency modulated coherent signal source comprises the microwave oscillator 8th , the synthesizer 9 and the quartz oscillator 11 could in turn by means of an arrangement according to the 2A or 2 B will be realized. The frequency range of the voltage controlled oscillator 8th (VCO) is chosen to be an integral part of the desired frequency range of the radar front-end. The transmit signal and the local oscillator signals for the receive mixers 5 be by frequency multiplication of the output signal of the voltage controlled oscillator 8th with two separate multiplier modules 50 and 51 generated. The multiplication factors of these blocks differ by value 1 , wherein preferably the larger value is used to generate the transmission signal. At the exit of the reception mixer 5 becomes such a bandpass signal he whose center frequency is that of the voltage-controlled oscillator 8th equivalent. This may be after filtering and amplification in respective receive amplifiers 52 with the output of the voltage controlled oscillator 8th in a respective further mixing stage 53 be converted into baseband. Since the output frequency of the voltage controlled oscillator 8th according to the frequency modulation changes over time, in this construction, unlike the embodiment of 4 the center frequency of the bandpass signal is not constant and much higher. The receiver amplifiers 52 and the other mixing stages 53 must therefore be realized at higher frequencies and relatively broadband.

With reference to the 6 Now is an extension of the radar front-end of the invention 4 explained on complex reception channels.

relative speeds and distances of moving targets become common with simple FM-CW radar by reversing the modulation slope d. H. resolved by triangular frequency modulation. There are So (at least) two frequency ramps with opposite slope for separation the speed and destination information of a range scan necessary. In similar Way, this statement also applies to transverse resolution and target speed with respect to the switching order of the combinations of transmitting and receiving elements. Be used instead of real recipients, complex receiver realized, so can the two consecutive opposite frequency ramps or element scans received information simultaneously with each a ramp or be obtained with an element scan. The time to record a radar image in moving scenarios can thus in half be reduced.

In 6 is shown as the real receiver arrangement 40 in 4 can be supplemented in a simple and advantageous manner to a complex receiver arrangement. After the intermediate frequency stage 45 the signal is split and put on a complex mixer 47 given, which converts the intermediate frequency signal into an in-phase and a quadrature signal in the baseband. Since the local oscillator signal of the other mixer 46 in the embodiment of the 4 frequency and low frequency, a good I / Q mixer can be realized easily and inexpensively. In the sensor basic structure according to 1 An I / Q mixer would have to be realized in the useful band of the radar front-end, ie at a high and also not constant local oscillator frequency.

Out From the above description it will be seen that the described Embodiments of present invention meet the described objects and achieved a number of advantages. These benefits include in an incomplete list: the Potential to cover multiple functions of forward facing automotive environmental sensors; the lateral resolution in an electronic way with moderate (compared to phased arrays) overhead of high frequency components; the simple and inexpensive Antenna technology (in comparison to the difference-lobe method); bandwidth-independent angular resolution moderate hardware costs; the maximum utilization of the available horizontal aperture for transverse resolution; the high flexibility, namely adaptability the sample rate and sample order of the transmit elements to the imaging requirements; the Maximum bandwidth efficiency through FM-CW method; the optimal one Target dynamic range through coherent Integration in distance and angular direction; the improvement of the target dynamic range by eliminating receiver amplitude errors a heterodyne receiving structure; the simple connection of a remote receiver element for extending the angle range to ± 90 ° and to optional application more coherent Triangulation method for very short distances, namely Parking assistance at distances less than 1 m; such as the slight degradation of image quality due to tolerances and changes the installation environment or by soiling the antenna surface.

If Features in the claims are provided with reference numerals, these reference numerals are only for better understanding the claims available. Accordingly, such reference numerals are not limited the scope of such elements, the only by way of example such reference numerals are indicated.

Claims (15)

Radar front-end comprising: a signal source ( 15 . 15A . 15B ), a plurality of transmission elements ( 1 ), which via a switching matrix ( 3 ) with the signal source ( 15 . 15A . 15B ) operably connected to the transmitting elements ( 1 ) to be sequentially supplied with a transmission signal; at least two receiving elements ( 2 ), wherein the transmitting elements ( 1 ) spatially between the receiving elements ( 2 ), and a device ( 20 ) for the digital control and processing of the received signals of the receiving elements ( 2 ), wherein the received signals parallel to the device ( 20 ). Radar front-end according to claim 1, wherein the Transmitting elements ( 1 ) are arranged similar and equidistant from each other. Radar front end according to claim 1 or 2, wherein the receiving elements 2 at the same distance from the respective adjacent transmitting element ( 1 ) are arranged. Radar front end according to one or more of the preceding claims, wherein the distance of the transmitting and receiving elements ( 1 . 2 ) is limited to a maximum of half the free space wavelength of the operating frequency of the radar front-end. Radar front-end according to one or more of the preceding claims, wherein the transmitting and receiving elements ( 1 . 2 ) have the same radiation pattern with the widest possible opening angle in the horizontal, so that the entire horizontal field of view of each individual element ( 1 . 2 ) is covered. Radar front-end according to one or more of the preceding claims, further comprising respective ones with the receiving elements ( 2 ) operatively connected receiving mixers ( 5 ), which are configured to homodyne the received received signals in parallel with a part of the transmission signal into the baseband, and further to a respective receiving mixer ( 5 ) related baseband stages ( 6 ) via respective analog-to-digital converters ( 7 ) the homodyne homodyne signal of the device ( 20 ) for digital control and processing. Radar front-end according to one or more of the preceding claims, wherein the signal source ( 15 ) is coherent, and where the signal source ( 15 ) a voltage controlled microwave oscillator ( 8th ) via a synthesizer ( 9 ) to a low-frequency quartz oscillator ( 11 ) is coupled. Radar front-end according to one or more of claims 1-7, wherein the signal source ( 15A ) is coherent, and where the signal source ( 15A ) a direct digital synthesizer ( 17 ), a fixed-frequency quartz oscillator ( 11 ), and a phase locked loop ( 16 comprising frequency divider, reference divider and phase frequency detector configured to generate a frequency modulated low frequency signal of high modulation linearity and coherence. Radar front-end according to one or more of claims 1-7, wherein the signal source ( 15B ) is coherent, and where the signal source ( 15B ) a fractional-n phase locked loop ( 18 ), which can be set to non-integer values. A radar front-end according to one or more of the preceding claims, further comprising one with a certain distance (D) to the transmitting and receiving elements ( 1 . 2 attached remote receiver assembly ( 30 ), wherein the distance (D) is chosen so as to allow a measurement by triangulation. Radar front-end according to claim 10, wherein the receiver assembly ( 30 ) comprises: a remote receiving element ( 31 ), a reception mixer ( 33 ), a baseband level ( 34 ) and one via a phase locked loop ( 35 ) controlled microwave oscillator ( 36 ), where the output of the baseband stage ( 34 ) with the device ( 20 ) is operatively connected to the digital control and processing, and wherein the phase locked loop ( 35 ) via preferably low-frequency signal lines ( 39 ) with the signal source ( 15A ) is coupled. Radar front end according to one or more of claims 1-5, wherein the signal source ( 15 ) a first synthesizer ( 9 ) for the generation of the transmission signal, and a second synthesizer ( 41 ) for generating a local oscillator signal, wherein the first and second synthesizers ( 9 . 41 ) is designed to generate the transmission signal and the local oscillator signal with the same frequency modulation but different absolute frequency, thus heterodyne to operate the radar front end. Radar front-end according to claim 12, further comprising respective intermediate frequency stages ( 45 ) associated with the respective outputs of the receiving mixers ( 5 ) and the intermediate frequency stages ( 45 ) downstream corresponding further mixing stages ( 46 ). Radar front end according to one or more of claims 1-5, wherein the signal source ( 15 ) a voltage controlled microwave oscillator ( 8th ) via a single synthesizer ( 9 ) to a quartz oscillator ( 11 ), and wherein the radar front-end further comprises two separate multiplier devices ( 50 . 51 ) capable of transmitting the transmit signal and a local oscillator signal to the receive mixers ( 5 ) by the frequency multiplication of the output signal of the oscillator ( 8th ) to thus heterodyne the radar front-end. Radar front-end according to claim 12, wherein the further mixing stage ( 46 ) as a complex mixing stage ( 47 ) is formed, which converts an intermediate frequency signal into an in-phase and a quadrature signal in the baseband.