EP1828805A1

EP1828805A1 - Radar system with adaptive digital reception beam forming and switchable transmission directional characteristics for coverage of near and far range

Info

Publication number: EP1828805A1
Application number: EP05808119A
Authority: EP
Inventors: Thomas Schoeberl; Thomas Focke; Thomas Hansen; Martin Schneider; Joerg Schoebel; Volker Gross; Oliver Brueggemann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-12-13
Filing date: 2005-11-18
Publication date: 2007-09-05
Also published as: CN101076741A; US20080258964A1; DE102004059915A1; WO2006063915A1

Abstract

The invention relates to a radar system, provided with a switch (40), for switching between at least two transmission antennae (41, 42) with different directional characteristics, in particular, for differing separation regions. A common analysis of the digitised signals for at least two receiver antennae (51, 52) is carried out in the receiver as a correlation of the receive antennae signals.

Description

RADAR SYSTEM WITH ADAPTIVE DIGITAL RECEPTION RAY SHAPING AND SWITCHABLE TRANSMITTER CHARACTERISTICS FOR COVERING CLOSE AND REMOTE RANGE

State of the art

In the field of driver assistance functions with predictive detection systems, radar sensors have primarily been used in the frequency range 76 to 77 GHz in the past few years

Commitment. These are still used in the upper class segment for the realization of the assistance function "Adaptive Cruise Control (ACC) in the speed range 30 to 180 km / h.

The radar sensors available on the market are characterized by the following

Properties from:

"Range up to approx. 120 ... 150 m, horizontal detection in the range ± 4 ° ± 10 °,

Angular accuracy about 0.5 °.

A limitation of today's sensors is that the overall depth is relatively large or the requirement of vehicle manufacturers for significantly flatter sensors can be met only insufficient.

The limit of the horizontal detection width, which consists of the selected

Antenna concepts resulting, is also disadvantageous because, for example, Einscherer only very late detected or relevant objects in tight curves more often disappear from the "field of vision." Here, especially for an automatic Staufolgeverfahren an extension of the field of view in the near to medium range is mandatory required. Here, for example, it is currently being considered to use additional sensors such as video or, for the ultralight range up to about 3 m, ultrasonic sensors.

Another essential limitation is that the radar sensors used hitherto, although objects in their angular storage in the above horizontal

Detection range can be determined very precisely (angular accuracy), but this is generally only possible reliably if only one object is to be detected at a certain distance and with a certain relative speed. If there are two or more objects at the same distance and they may also have the same speed, then today's radar sensors can only be single

Separate objects if the radar lobe or the half-width of the radar lobe is narrower than the angular distance of the objects to be separated. For a given half-width of an antenna beam, however, a given size of the antenna aperture is required for a given frequency or wavelength. In the case of a circular antenna aperture with the diameter D and a constant coverage, approximately the following relationship applies for the half-width υ in degrees:

υ - 59 ° - D

with the wavelength λ (λ = 3.9 mm at 77 GHz). If, for example, a

An angular separation of at least 2 ° can be achieved, so an aperture diameter D> 115 mm would already be selected according to the above formula. This is not acceptable for an ACC sensor, as the maximum permissible size is limited to significantly smaller dimensions. On the other hand, such a separation capacity of about 2 ° and possibly even less is required to a clear lane assignment for larger

To perform object removals. The aperture diameter D of an exemplary sensor is, for example, 75 (60) mm. This results in the minimum possible half width for a single radar lobe to 3.1 ° (3.8 °). The real half-width is much larger, since a constant Aperturbelegung not done, but decreases the occupancy to the edge. With decreasing Aperturbelegungen to the edge of the pre-factor increases in the above formula (59 °) at revalues between 80 ° ... 100 °, that is, the half-value range is in the range of 4.2 ° ... 5.2 ° (for D = 75 mm) or 5.2 ^o ... 6.5 ^o (for D = 60 mm). From DE 197 14 570 Al a multi-beam radar system is known in which more transmitting elements are present as receiving elements, wherein the existing transmitting elements both singly and in any simultaneous combination can be switched on. The reception elements can also be switched. Thus, the observable angle range can be widened.

WO 2004/051308 A1 relates to a device for measuring angular positions using radar pulses and mutually overlapping antenna beam characteristics of at least two antenna elements. At the receiving end, a common evaluation of received signals of at least two antenna elements takes place.

Advantages of the invention

With the measures according to claim 1, that is, in a radar system consisting of at least two transmitting antennas with two different directional characteristics, in particular for different distance ranges, a switch for switching between at least two different directional characteristics, at least two receiving antennas, an evaluation device for the common evaluation of the digitized signals at least two receiving antennas in the sense of a correlation of the receiving antenna signals, can be a very wider horizontal

Detection area, e.g. up to ± 40 °, at medium ranges (1 ... 50 m), e.g. for early detection of scrapers in this distance range, and a narrow horizontal detection range, e.g. ± 6 °, reach at long ranges (80 ... 150 m).

The different distance ranges can be switched flexibly and optionally dynamically. Due to the possibility of using digital evaluation methods, a high angle separation, in particular by parameter estimation methods, can be achieved. For a secure detection of a lane situation or a separation of closely adjacent and possibly very different vehicles is possible. By

Use of planar radiators, in particular patch elements which can be controlled individually or in particular by columns, can be achieved with a low structural depth. The front-end design of the radar system is scalable, which means that the front-end can be adapted to special requirements, such as locating field, range, and thus eg in the rear area by means of special embodiments - A -

Use find for dead-angle monitoring, lane change assistant, etc., possibly also with another embodiment of the digital signal evaluation. The invention allows the use of modern evaluation methods, whose angular separation power is not directly related to the size of the radiating aperture, but theoretically is almost independent of this.

Such methods are known by the term "subspace-based parameter estimation methods" since the mid-1980s The most important representatives are the methods Music and Esprit These approaches are based on the use of several parallel antenna elements on the receiving side, each with the same, overlapping directional characteristics and the evaluation of the

Correlation properties of these quasi time synchronously present parallel received signals by means of digital signal processing. These approaches, with sufficient signal-to-noise ratio (S / N signal to noise ratio) at the receivers, allow highly precise angular separation even with greatly different reflectivity of the objects to be separated.

For the realization of such antenna arrangements, the use of planar antenna structures, such as so-called patch antennas, or other planar antenna structures such as dipoles or short, empty end stubs ("stubs") are particularly advantageous, which also offer the possibility of maximum flat front ends for In order to realize maximum horizontal detection without so-called "grating praise" with corresponding ambiguities in the angle estimation, the parallel individual radiators preferably have a spacing of the order of half the free-space wavelength, ie approximately 2 mm at 77 GHz.

When using such parallel arrangements so-called digital beam forming methods are used in which a bundled beam lobe is formed only by digital signal processing, but not in the analog high-frequency plane as in a lens antennas or parabolic antenna. The digital beam shaping is particularly advantageous for the detection of distant objects, as this sufficient S / N is formed and so a reliable location is possible. In previous frontends with digital beam shaping, the field of view is limited to approximately ± 10 ° and thus can only be used to a limited extent for the functions which require a significantly wider azimuthal detection of the vehicle environment ahead.

In the invention, the receiving side on the high-frequency level no need

Beam lobes are formed, but the received signals of individual antenna columns directly digital, or after appropriate digitization, further processed (digital beam shaping) in the sense of a correlation of the antenna signals. In multi-objective scenarios, the constraints of beamforming at the digital level can be circumvented by using high resolution estimation techniques for angle determination.

drawings

Reference to the drawings embodiments of the invention will be explained in more detail. Show it

FIG. 1 shows a block diagram for a radar front end,

FIG. 2 shows a single antenna element,

FIG. 3 series-fed antenna elements, FIG. 4 antenna elements fed in parallel,

FIG. 5 and FIG. 6 embodiments of transmitting antennas with a plurality of individual radiators,

FIG. 7 shows a transmitting antenna designed as a single element,

Figure 8 shows a transmitting antenna executed with several individual elements and more specific

Connection, Figure 9 shows a radar front end with two different local oscillator frequencies for

Send and receive branch,

FIG. 10 the switching between two transmitting antennas,

FIG. 11 Connection / disconnection of elements within an antenna,

Figure 12 to 14 reception concepts with extension by amplifiers and multiplexers, Figure 15 shows the distribution of the local oscillator signal with repeaters.

Description of exemplary embodiments

FIG. 1 shows a block diagram for a radar front end 1. This front end 1 consists in detail of: a possibly stabilized via a PLL and optionally via a DRO, modulatable, preferably in so-called MMICs highly integrated 77 GHz source 2 (so-called modulated local oscillator), a transmitting unit 4 consisting of: - at least two different transmit antennas 41 and 42 in planar technology

(Antenna patch), of which an antenna 41 is designed so that it generates a comparatively highly concentrated antenna lobe by corresponding superposition of the waves belonging to the antenna 41, a further antenna 42 which is designed so that they by appropriate superposition of the waves to antenna 42 belonging to individual radiators a comparatively broad azimuthal antenna characteristic generated or consists of only one radiating element, optionally further transmit antennas which are designed so that they generate further, special transmission characteristics, a 77 GHz switch 40 for switching between the different transmitting antennas, that is between the Antennas 41 and 42 and optionally further antennas, a receiving unit 5 consisting of at least two parallel, receiving individual emitters 51 and 52 and optionally further in planar technology (patch antennas), the received signals by a mixer unit 50 in u nmittelbarer antenna proximity are mixed down into an intermediate frequency band (baseband), and a power divider 3, so-called Tx-Rx power divider, for dividing the

Local oscillator power of the 77 GHz source 2 in the respectively required in the transmitting unit 4 and in the receiving unit 5 shares.

The respective individual emitters 43 of the transmitting antennas 41, 42 and receiving antennas 51, 52 may, as shown in FIGS. 2 to 4, consist of a single patch 60 or of a plurality of vertically stacked patches (antenna gaps). The latter is in the absence of further bundling units, e.g. Cylindrical lens, advantageous to both the transmitting and receiving side in the elevation plane, the energy parallel to

Bundle road level. The feeding of the patches in a column takes place as series feed 61, parallel feed 62 (corporate feed) or as a combination thereof. A radiation-coupled supply, for example via multi-layer slot patch or patch patch couplings, is also possible. The antenna column is thus arranged perpendicular to the road surface. Bundling in elevation could be both send and receive also be carried out at the receiving end by using a cylindrical lens, then a single radiator would be represented by a single patch. Their focal line would then correspond approximately to the center lines of the individual patches.

It is essential that based on the azimuthal level of the transmitting unit 4 so-called analog beam forming methods should be used, while the receiving unit 5 is designed so that together with a downstream evaluation so-called digital beam forming methods are used. This is achieved essentially by parallel receiving single emitters with a quasi-parallel, optionally also guided via a multiplexing unit, further processing. Only this digital approach on the receiving side by parallel operated individual receiving antennas or receiving individual emitters 51, 52 and optionally further allows the use of methods that have a high separability at an angle, i. significantly lower than the half width of a collimated radar lobe.

To represent the 77 GHz source 2, commercially available chips or chipsets in MMIC technology or other 77 GHz generating elements such as e.g. Gunn elements are used.

The first transmission antenna 41 is shown in FIG 5 by the use of several

Single radiator 43 and their connection to RF analog signal level 44 realized. The analog connection 44 in the sense of a power divider allows e.g. the assignment of the individual emitters by a certain amplitude distribution. This can e.g. be chosen so that the so-called side lobes of the antenna 41 occupy a very low level below the main lobe, e.g. -30 dB. As a result, in contrast to conventional sensors, it is possible to minimize disturbances caused by "illumination" of objects outside the main lobe For example, the use of seven individual radiators in antenna 41 permits a main lobe width of ± 6.5 ° with a lowering of the side lobes Figure 6 shows a variant of four columns of individual radiators 43.

The second transmitting antenna 42 is used to achieve the widest possible azimuthal illumination. For example, the use of a single radiating element in antenna 42 according to FIG. 7 enables a main lobe width of approximately ± 40 °. But it is also quite possible, through the targeted design of a multi-element Antenna 42 with a special power divider 45 (according to Figure 8) to achieve larger main lobe widths than ± 40 °.

The use of the high-beam antenna 41 would allow objects at a great distance, e.g. 80 m ... 150 m, but only in a narrow angular range.

This has the advantage that disturbances of roadside developments, in particular guardrails, can be greatly reduced.

The use of the azimuthally broad-emitter antenna 42 would allow objects of e.g. in the run-up to the ego vehicle in a very wide azimuthal detection area to locate. Since the 77GHz energy is not focused, but radiated "wide", distant, objects are only slightly illuminated, so that their reflections are low and therefore not disturbing Antenna 41 would thus be the antenna for the operating mode LRR (Long Range Radar) while Antenna 42 would be used for the MRR (Medium Range Radar) or SRR (Short Range Radar) mode and would, for example, serve timely detection of pruning shears or other relevant objects in the outer (near to mid range) range Modes MRR / SRR is that the receiving individual emitters 51, 52 and possibly further have a broad azimuthal beam characteristic.The overall unit with the described switching options can be referred to as a URR (Universal Range Radar).

Other transmission antennas may be used to e.g. to generate further specific transmission characteristics, e.g. azimuthal or optionally also vertically tilted beams, that is radar beams whose maximum does not point in the direction perpendicular to the front end but in different directions. Also, the antennas 41 and 42 could already be designed so that their main beam directions already have directions deviating from the vertical of the front end, e.g. to allow certain installation scenarios on the vehicle where the sensor has e.g. can not run perpendicular to the vehicle axis.

Usually, the respectively used transmitting antenna 41 or 42 or possibly further emits a modulated 77 GHz signal. This may be, for example, an FMCW, pulse, FSK, pseudonoise (PN) or else further customary radar modulation methods, or else combinations of the methods mentioned. The 77 GHz switch 40 is used for switching between the different transmission antennas, that is, in the switching mode a) transmits only the antenna 41 and in switching mode b) only antenna 42. Other switching modes can optionally further antennas with other special transmission characteristics available

Radiate transmission power. Such 77 GHz switches are already available in integrated technology (MMICs), but can also be realized by using so-called PIN diodes in a discrete design.

The receiving unit 5 with the receiving individual radiators 51 and 52 and optionally further serves to receive the waves reflected at individual objects. Depending on the type of modulation, it is also possible to deduce the relative speed of these objects from a frequency offset, a transit time or a phase difference relative to the transmission signal, and via the so-called Doppler effect. Furthermore, the reflected waves fall on the parallel, receiving

Single radiators obliquely and therefore with different phase relationships, if these objects have a lateral offset to the normal of the antenna front end. By analyzing these phase relations, the angular deviation of these objects can also be calculated. Classical methods such as the monopulse method perform this analysis by comparing the magnitude of a plurality of received signals from azimuthally overlapping beam lobes. The monopulse process can be carried out both with so-called analog-shaped beam lobes, which are e.g. can generate over a dielectric lens, or one generates these overlapping beam lobes only by digital signal processing (digital beam forming) in the evaluation. Another method would be to scan the image horizontally

Detection area with only one beam lobe. In this case, the angular deviation from the amplitude distribution over the angle would have to be determined. But in all these so-called classical angle estimation methods, the separability is limited to the half-width (n) of the beam lobe (s).

The invention described here relates in particular to digital beamforming with respect to the receiving unit. In this case, the received signals of a plurality of receiving individual emitters, which are applied in parallel in the receiving unit, are mixed down into the analog baseband via a mixer unit 50, amplified and filtered, digitized and multiplied in the processor unit by complex weighting factors and finally added, ie a correlation, in particular weighted summation, of different individual radiators in the digital range is undertaken. This approach then also produces beamformed signals, but only digitally. For the angle estimation, monopulse or continuous scanning can also be used. In addition, however, methods are also applicable which are not subject to the limitation of the angular separation capability to the half-width of the beam lobes. By analyzing the received signals into a so-called signal and noise subspace, the possibility of a very high angular separation capability results.

The power divider 3 may be realized in the form of a so-called Wilkinson divider, a so-called T-divider, a ring hybrid or a line coupler. Other embodiments are a planar lens, e.g. Rotman lens, or a divider with one / more integrated power amplifiers (active power splitter)

MMIC can be constructed.

All 77 GHz line elements are preferably constructed in microstrip technology, but the invention is independent thereof.

In the following, alternative embodiments and realization details are shown:

more than two transmitting antennas, - more than two receiving individual elements,

77 GHz source realized by MMICs or Gunn element,

77 GHz source stabilized / modulated by a PLL unit and optionally a DRO, two sources 21 according to Figure 9 with different frequencies f \ and Ϋ2 for transmitting and receiving branch: thus the system works at the receiving end with a

Intermediate frequency (sources may refer to a reference 20, for example, by divider / PLL or multiplication).

FIG. 10 shows a first embodiment of the change-over switch 40 within the transmitting unit 4 in the form of switching between the antennas 41 and 42 and FIG 11 shows an embodiment in the form of the connection / disconnection of elements within an antenna: it is switched between the antennas 41 (part of the entire antenna) and 42 (entire antenna).

Figures 12 to 14 show the receiving unit 5 extended to LNA (Low Noise

Amplifier 70), multiplex unit 71 and IF preamplifier 72. In a first variant according to FIG. 12, the mixer unit 50 is expanded by LNA 70 and / or IF preamplifier 72. In a second variant according to FIG. Unit 71 a plurality of receiving antennas 51, 52 successively to the mixer unit 50, which may be extended by LNA 70 and / or IF preamplifier 72. The multiplex unit serves to reduce the number of receiving channels to be processed. In a third variant according to FIG. 14, the multiplex unit 71 successively switches a plurality of receiving antennas 51, 52 with associated LNAs 70 onto the mixer unit 50, which may be extended by LNA and / or IF preamplifiers. The latter variant is advantageous if the noise of the multiplex unit is too high.

FIG. 15 shows an extension of the Tx-LO distribution with amplifiers that may be used at one or more of the positions 80, 81, 82, 83. Preamplifier 80 between Tx-Rx power divider 3 and the mixer unit 50 of the receiving unit 5 or preamplifier 81 within the LO distribution in the receiving unit to the individual

Mixers serve to provide the required local oscillator power levels for a sufficiently good mixing process (in terms of mixer conversion losses and mixer overhead noise). Their use depends on the design of the power divider 3, the number of receiving single radiators and the chosen mixer concept. Alternatively / additionally, an amplifier 82 between Tx-Rx

Power divider 3 and the transmitting unit 4 or one or more amplifiers 83 between antenna switch 40 and one or more transmitting antennas 41, 42 are used.

Power divider 3, switch 40, mixer unit 50 to LNAs 70 advanced

Mixer unit, multiplex unit 71, preamplifier 80 and IF preamplifier 72 may be partially discrete, partially highly integrated in MMICs or all together in one MMIC highly integrated. The bundling properties in elevation of the transmit antennas 41, 42 and optionally further may be different. The Bundling properties in elevation of the receiving individual emitters 51, 52 and optionally further may also be different.

In automotive radar systems FMCW (frequency-modulated continous wave) modulation is frequently used. In order to separate distance and speed information, two or more modulation ramps with different parameters (e.g., ramp slope) must be used. The necessary assignment of the frequency lines generated by the targets in the individual ramps to one another is particularly difficult in the case of separate processing / digitization of the signals from (planar) individual elements (as used, for example, for the subspace-based parameter estimation methods), because at the receiving end there is no restriction of the antenna characteristic in azimuth or at best a restriction to the area of near / MRR / mode exists. Thus, in principle, reflections from all targets in the detection range of the receiving antenna are received, so that the assignment of the frequency lines to one another becomes very difficult, if only by the number of targets. Especially in the far range, the number of detected targets in the detection range of the receiving antennas can become extremely large. Therefore, additional measures must be taken to ensure as far as possible that only signals from targets that are relevant to the respective operating state are received or processed. The following are preferably used for this purpose

Activities:

the characteristic of the transmitting antenna for the long range is limited to a relatively narrow angular range in the order of ± 4 ° to ± 8 °, so that on the highway curves are still sufficiently lit, but otherwise only

Targets are irradiated in the driving tube. The side lobes of the transmitting antenna must also be suppressed as much as possible, because targets in the vicinity, such as crash barriers, which are irradiated on the side lobes, would otherwise lead to relatively strong received signals. This makes it necessary to introduce a second operating state for the near range. In this operating state, a transmitting antenna with wide azimuthal beam characteristic is used, because for applications in city traffic, eg Staufolgefahren, pre-crash functions, etc., a large angular range in azimuth, eg ± 60 °, must be covered. Since in the operating state near range no very high range is required, the transmission power can be reduced in addition to the anyway lower antenna gain due to the wide main lobe coupled to the switch to the near range. This desirably reduces the range.

Targets that are not within the range covered by the current operating condition can be suppressed for FMCW modulation by an appropriate filter for the baseband signals switched to operating state. The baseband frequency caused by the distance is significantly larger than the baseband frequency by the Doppler shift. Thus, e.g. with a

Highpass filter for the far range the near targets and with a lowpass filter for the near range the distant targets are suppressed. For the corner frequencies of the filter, a certain overlap of the passbands must be provided because of the range uncertainty caused by the Doppler components. The mentioned filter characteristic is usually still accompanied by an additional high-pass filter.

Characteristic superimposed. The latter is used to partially compensate for the range dynamics (receive power is proportional to R "^) and the parameters of the modulation (for example, ramp slope in FMCW) should be selected accordingly.

The reduction of the number of detected targets described here in the respective

Distance range relevant angle range also has a favorable effect on the tracking of the targets. In general, the quality of the target detections of an FMCW ramp pass is not so good that all targets are reliably detected and determined in position. Furthermore, there are ghost echoes and not clearly resolvable assignments of the frequency lines. These uncertainties can be eliminated if

Targets are stored and tracked over several ramp passes in a target list, possibly with prediction of the expected position and confirmation of a target only after repeated consistent detection. This so-called tracking becomes all the more difficult and computationally more, the more goals are to be processed. A reduction in the number of goals to be processed is also very helpful here.

A range of the input level of -120 ... +5 dBm should be tolerated by the input stage (mixer) if necessary LNA. In the far-range mode, an override of the input stage is acceptable as long as only intermodulation products of the strong signals from the near range occur. These Intermodulation products are in baseband just like the associated input signals at low frequencies and are removed by the switchable filter described above. In short-range mode, on the other hand, the transmit power must be lowered so that no overmodulation and intermodulation occur.

For digitization with sufficiently fast and low-cost A / D converters, the baseband dynamics must be limited to a range of approx. 60 dB (10 bits). This is done in the far-field mode by the high pass characteristic of the LF signal path, which suppresses low frequency components. By reducing the transmission power in the near range, the requirements for the switchable filter and the associated switching of the AF gain can be reduced.

If the column spacing is greater than half the free space wavelength, ambiguities in the angle determination occur (analogous to grating lobes = higher

Diffraction orders in beam shaping). Therefore, the column spacing must either not be significantly greater than half the free space wavelength or the side lobes of the transmitting antenna in the region of the grating lobes must be so small that no targets are detected there.

The height of the targets in elevation is maximally 4 m (truck) typically approx. 2 m. Since it is not known in advance which areas of a vehicle represent the strongest radar targets, long-distance passenger cars and motorcycles should be irradiated at their full height (trucks generally have much stronger radar targets). At close range, goals do not have to be fully captured because of the lower

Distance even weaker reflection centers at the destination produce a sufficient received signal. In the width of the beam lobe should also be included a certain tolerance against pitching and / or loading of the vehicle. An opening angle of typically 3 to 4 ° is thus sufficient for long-range (2 m height in 30 m distance). At the same time, this narrow main lobe reduces reflections from the ground that lead to unwanted signals or clutter.

However, an opening angle of 4 ° at a distance of 3 m illuminates only an area of about 20 cm in height, in which a reflection center would have to be. Therefore, an increase in the opening angle for close range to about 5 to 20 ° (I m height in 3 ... 10 m distance) necessary. It should be sufficient to irradiate the areas where usually the strongest reflections occur (license plate and surrounding areas, wheel arches, ...).

The following summarizes the important features:

Antenna switching of the transmitting antenna for two distance ranges, short-range: as broad and flat characteristics as possible for detection of radar targets up to a first distance limit (or frequency limit with FMCW modulation),

Long-range: main lobe designed to cover the lane on highways or highways incorporating typical curve radii (typically ± 8 °, reasonable range approximately to ± 4 ° to ± 12 °), and minimized sidelobes (typically -30 dB and lower) ; Processing of the detected radar targets takes place only from a second distance limit (resp.

Frequency limit with FMCW modulation), overlapping of the distance limits,

Digitally processed, in particular, a plurality of antenna columns on the receiving side, and digitized into the baseband, wherein a switching over of the columns can occur,

Columns of the receiving antenna with wide beam characteristic in azimuth, such as. Single patches arranged in elevation to a column.

Optionally, these features may be combined with at least one of the following features:

1. Broad-range transmit antenna has a relatively narrow lobe in elevation, about 3 to 5 °, near-range transmit antenna has a wider main lobe in elevation, e.g. 20 °,

2. switching the characteristic of the baseband filter, if necessary, with switching of the amplification,

3. reduction of the transmission power for the mode close range, 4. modulation switching (FMCW parameter or other modulation principle (Doppler, pulse Doppler, FSK)),

5. Switchable LNAs in front of the mixers,

6. Use of high-resolution angle estimation methods together with digital beamforming and classical evaluation methods.

Claims

claims

1. radar system comprising: at least two transmitting antennas having different directional characteristics, in particular for different distance ranges, - a changeover switch (40) for switching between at least two different transmission characteristics, at least two receiving antennas (51, 52), an evaluation device for the common evaluation of the digitized signals of at least two receiving antennas in the sense of a correlation of the receiving antenna signals.

2. Radar system according to claim 1, characterized by a receiving side digital beam shaping.

3. Radar system according to claim 1 or 2, characterized in that the

Evaluation device is designed so that the detection of radar targets can be selected by distance ranges.

4. Radar system according to one of claims 1 to 3, characterized in that a very wide horizontal directional characteristic is provided for a near area and for a long range a narrow directional characteristic.

5. Radar system according to one of claims 1 to 4, characterized in that the different directional characteristics are realized by superimposing the directional characteristics of a plurality of individual antenna elements.

6. Radar system according to one of claims 1 to 5, characterized in that a modulable local oscillator (2, 20) is provided with a power divider for dividing the local oscillator power for transmitting and receiving unit.

7. Radar system according to one of claims 1 to 6, characterized in that the signals of the at least two receiving antennas are mixable down via a mixer unit in the analog baseband and after digitization with complex weighting factors are multiplied and added.

8. Radar system according to one of claims 1 to 6, characterized in that the signals of the at least two receiving antennas undergo a subspace-based parameter estimation method for analyzing their correlation properties.

9. Radar system according to one of claims 1 to 8, characterized in that a receiving-side multiplex unit (71) is provided, by means of which the signals of a plurality of receiving antennas are successively switchable to a mixing unit.

10. Radar system according to one of claims 1 to 9, characterized in that the different distance ranges or their associated directional characteristics are formed overlapping and the processing of the detected radar targets takes place only from a predetermined minimum distance limit.

11. Radar system according to one of claims 1 to 10, characterized in that as

Antenna elements patch single radiators and / or columns of individual radiators are provided, which are operable in series or parallel feed.

12. Radar system according to one of claims 1 to 11, characterized in that a switchable Basisbandfϊlter is provided, the targets outside of a selected

Distance range suppressed.

13. Radar system according to one of claims 1 to 12, characterized in that means are provided for reducing the transmission power for operation in a vicinity.