DE102016222474A1 - Radar sensor arrangement on a motor vehicle - Google Patents

Abstract

Radar sensor assembly on a motor vehicle (10), with at least two angular resolution radar sensors (12), which together with a control and evaluation (14) form a cooperative radar system, characterized in that the radar sensors (12) each have a group antenna with a in the direction of Angular resolution curved aperture (16) have.

Description

The invention relates to a radar sensor arrangement on a motor vehicle, with at least two angle-resolving radar sensors, which together with a control and evaluation device form a cooperative radar system.

State of the art

Radar systems for driver assistance systems have long been installed in vehicles. With the aid of these radar sensors, distance, speed and angle to objects within a radar field of view can be detected. In most cases, only a single sensor with a restricted field of vision is installed in vehicles, e.g. for monitoring vehicles in front. In the course of the functional expansion of the driver assistance systems, however, an increasing number of independently operating radar sensors are used which cover a larger field of view, e.g. the entire front area with a field of view of up to 180 °. In this case, e.g. a so-called mid-range radar sensor (MRR) may be arranged centrally on the vehicle front side, and additional MRR sensors may be located on the front vehicle corners. The sensors each have a planar antenna whose angular estimation accuracy depends on the angle.

Out DE 10 2013 008 953 A1 a radar sensor arrangement of the aforementioned type is known which has at least two Einzelradarsensoren forming a radar system in which a signal emitted by a first radar sensor and reflected at a single object signal is received by another radar sensor, which then emits a signal to the the same one object is reflected and received by the first radar sensor. By means of this so-called bistatic or cooperative operation of the sensors, in which the sensors no longer operate independently of one another, additional information about the detected object can be generated.

Out DE 10 2014 208 389 A1 a single radar sensor for motor vehicles is known in which a plurality of antenna elements, which are formed by openings of waveguides, are arranged in angled surfaces to each other, so that radar radiation is radiated in different directions and can be received from different directions.

Disclosure of the invention

The object of the invention is to provide a radar sensor arrangement on a motor vehicle, which enables improved angular estimation accuracy with low installation costs.

This object is achieved in that the radar sensors each have a group antenna with a curved in the direction of the angular resolution aperture surface.

The array antennas of the radar sensors are therefore so-called conformal antennas, in which the individual antenna elements have different orientations and thus also different directional characteristics due to the curvature of the substrate. This has the advantage that the field of view of a single radar sensor is increased. In a cooperative system, the necessary overlap between the fields of view of two adjacent radar sensors can still be achieved even if the sensors are arranged at a greater distance from one another. At the same time, the accuracy of triangulation measurements is improved due to the larger base width. Likewise, the larger fields of view of the radar sensors allow the orientations of the two radar sensors to diverge more, so that given a number of sensors, the overall field of view of the complete system can be increased, or for a given total field of view, the number of radar sensors can be reduced can.

A further advantage is that due to the curvature of the aperture surface, the angular estimation accuracy of the single radar sensor is less dependent on the angle of the located object, so that the angular estimation accuracy for objects at the edge of the field of view is similar to that for objects in the center of the field of view. An advantage of the conformal antennas is also that a uniqueness of the angle measurements can be achieved even at larger distances between the individual antenna elements of the array, so that for a given aperture, the number of antenna elements and thus the number of evaluation channels can be reduced or vice versa given number of antenna elements, the aperture can be increased.

Advantageous embodiments and further developments of the invention are specified in the subclaims.

In an advantageous embodiment, the curved substrate of the compliant antenna follows the curvature of a body part of the vehicle on or behind which the relevant radar sensor is installed. This allows a space-saving arrangement of the radar sensors, for example in the corners of the vehicle and at the same time helps to avoid installation artifacts.

In an advantageous embodiment, the radar sensors are arranged on the vehicle, for example, at the four corners, that together they cover the entire vehicle environment, that is, have a total field of view of 360 °. Accordingly, with only two radar sensors, a field of view of 180 ° or more can be achieved.

In the following embodiments are explained in detail with reference to the drawing.

• 1 ein Beispiel für eine Anordnung von vier Radarsensoren mit konformen Antennen in den Ecken eines im Grundriss dargestellten Kraftfahrzeugs;
• 2 eine perspektivische Ansicht einer konformen Antenne eines einzelnen Radarsensors;
• 3 eine Grundrissskizze eines Fahrzeugs auf einer mehrspurigen Fahrbahn, zur Illustration des prinzipiellen Aufbaus eines Sensornetzwerkes mit einem 360°-Gesichtsfeld;
• 4 ein Diagramm zur Illustration der Anordnung von Antennenelementen eines Antennenarrays in einer Ebene (x-z Ebene), in der der Radarsensor winkelauflösend ist, einmal für eine konforme Antenne und einmal für eine planare Antenne;
• 5 ein Diagramm zur Illustration einer Richtcharakteristik des planaren Antennenarrays gemäß 4;
• 6 ein Diagramm zur Illustration der Richtcharakteristik des konformen Antennenarrays gemäß 4;
• 7 ein Beispiel für ein Winkeldichtespektrum bei Ortung eines einzelnen Objekts mit dem planaren Antennearray gemäß 4;
• 8 ein Winkeldichtespektrum für die Ortung desselben Objekts wie in 7 mit dem konformen Antennearray gemäß 4; und
• 9 ein Diagramm zur Illustration der Winkelabhängigkeit der effektiven Apertur bei einer planaren Antenne.

Show it:

• 1 an example of an arrangement of four radar sensors with conformal antennas in the corners of a plan view motor vehicle;
• 2 a perspective view of a conformal antenna of a single radar sensor;
• 3 a Grundrissskizze a vehicle on a multi-lane road, illustrating the basic structure of a sensor network with a 360 ° field of view;
• 4 a diagram illustrating the arrangement of antenna elements of an antenna array in a plane (xz plane) in which the radar sensor angle-resolving, once for a compliant antenna and once for a planar antenna;
• 5 a diagram illustrating a directional characteristic of the planar antenna array according to 4 ;
• 6 a diagram illustrating the directional characteristic of the conformal antenna array according to 4 ;
• 7 an example of an angular density spectrum in locating a single object with the planar antenna array according to 4 ;
• 8th a angular density spectrum for the location of the same object as in 7 with the compliant antenna array according to 4 ; and
• 9 a diagram illustrating the angle dependence of the effective aperture in a planar antenna.

In 1 is a floor plan of a motor vehicle 10 shown that a radar sensor assembly with four radar sensors 12 has, which are respectively arranged in the corners of the vehicle body. The radar sensors 12 are with a central control and evaluation device 14 connected and together with this control and evaluation a cooperative sensor system. Each of the radar sensors 12 has a conformal array antenna with a curved aperture surface 16 , which is adapted to the curved course of an associated part of the vehicle body. For example, the antenna substrate 16 be arranged directly behind a body part made of plastic, which is permeable to radar radiation.

In 2 is in perspective a single antenna assembly 17 shown in this example the curved aperture surface 16 is formed and formed by a one-dimensionally curved plate of an electrically conductive material, are formed in the waveguide, which open in the convexly curved aperture surface and there antenna elements 18 form a group antenna.

The antenna assembly 17 is installed in the vehicle such that the axis of curvature of the aperture surface 16 vertically (in the direction of the y-axis), so the plate is curved in the horizontal xz-plane. The antenna elements 18 are arranged in the surface of the plate in vertical columns and horizontal lines. In each column have the antenna elements 18 equal distances, so that a bundled directional characteristic is achieved in elevation. The distances between the individual antenna columns in the direction x are chosen such that, in cooperation with the curvature of the antenna substrate, a desired, further fanned out directional characteristic is achieved in the azimuth.

In the example shown, the antenna elements form 18 a matrix-shaped receiving array 20 and a transmit array disposed separately therefrom 22 , In the waveguide whose mouths the transmitting array 22 is formed by a in 2 Not shown high-frequency part coupled microwave radiation, which then via the openings of the waveguide, so the antenna elements 18 is emitted. The received radar echo is from the antenna elements 18 of the receiving array 20 coupled into associated waveguide and forwarded to a receiving part in the high-frequency part.

In another embodiment, the antenna elements 18 are also formed by flat patches on the surface of the antenna substrate, in which the microwave power is fed, for example via microstrip lines.

In 1 is for each of the radar sensors 12 schematically an associated field of view 24 shown, which consists of several partial viewing areas 26 composed of individual antenna columns. The partial viewing areas 26 a single radar sensor 12 are due to the curvature of the antenna substrate 16 mutually angularly offset, but overlap each other relatively strong, so that each located object in several partial viewing areas 26 Thus, by analyzing the amplitude and phase relationships between the signals received from the various antenna columns, an estimate of the directional angle of the object can be made.

In 1 it can also be seen that also the viewing areas 24 the two rear radar sensors 12 overlap. For larger object distances overlap each other and the viewing areas 24 the two front radar sensors 12 , And at even greater distances there is also an overlap between the field of view of the radar sensors on the left side of the vehicle and between those on the right side of the vehicle. This allows a cooperative operation of the radar system in which a radar signal transmitted by one of the radar sensors, after reflection at the object, is not only received by the same radar sensor, but also by at least one of the two adjacent radar sensors. In one operating mode, the radar sensors can alternately transmit and receive. However, an operating mode is also possible in which all the radar sensors simultaneously transmit and receive, wherein an assignment of the received signals to the transmitting radar sensor is possible for example in that the radar sensors transmit in frequency bands shifted slightly relative to one another. In any event, by offsetting the signals sent alternately from one sensor and received by the other sensor and the signals received back from the transmitting sensor itself, the accuracy of the distance and angle measurements can be significantly improved.

In the example shown, all four radar sensors communicate 12 with the central control and evaluation device 14 , In another embodiment, however, the control and evaluation could also be integrated into one of the radar sensors.

Conveniently, the arrangement is such that each radar sensor 12 has its own high frequency part, so that only the mixed down in a lower frequency band intermediate frequency signals to the evaluation and control device 14 and / or to be communicated to the other radar sensors. It would also be conceivable for the intermediate frequency signals to be in place in each individual radar sensor 12 be digitized and the radar sensors and the control and evaluation only exchange digital signals with each other, which allows communication via a digital bus system.

In 3 are the equipped with the radar sensor assembly vehicle 10 as well as antenna diagrams 28 of the conforming antennas of the radar sensors, which in this example provide a 360 ° all-round view. The network of radar sensors (not shown in detail here) 12 allows different modes of operation with which locating ranges 30 . 32 . 34 to configure the traffic environment according to the situation. In the example shown, the location area is used 34 for detecting preceding vehicles 36 with relatively long range, the detection range 30 serves to capture subsequent vehicles 38 , also with a relatively long range, and the detection range 32 has a lower detection depth, but extends over a larger angle, so that in the immediate vicinity also vehicles 40 on side lanes as well as objects on the roadside can be detected.

In a radar sensor with a conventional planar antenna in the direction in which the angular resolution is to be achieved, here in the x-direction, the distance between the individual antenna elements or antenna columns may not be greater than λ / 2 (λ is the wavelength of Radar radiation), if a clear angle estimation should be possible. In the case of compliant antennas with a curved antenna substrate, this restriction does not apply. This is in 4 illustrates where with triangles the Positions of the antenna elements 18 or antenna columns of a compliant antenna are shown in the xz plane, while with circles the positions of antenna elements 18 ' a planar antenna having the same number of antenna elements (or columns) and the same aperture.

5 and 6 show the associated directional characteristics. The normalized power as a function of the x-component u _{x of} a direction unit vector u (in each case is shown). 2 ). 5 shows the case of the planar antenna, in which all antenna elements 18 ' have the same directional characteristic. 6 shows the directional characteristics of the antenna elements 18 due to the curvature of the antenna substrate 16 differ from each other and thus cover together a larger angular range.

7 and 8th show associated angular density spectra, which give information about the most probable result as well as about the reliability of an angle estimation.

In the example shown, it was assumed that the true position of an object is u _x = 0.3. When the angle estimation based on the amplitudes and phases of the antenna elements 18 ' the planar antenna received signals is made, then the probability determined by this data that the object is in the direction u _x , through the curve 42 in 7 specified. Accordingly, a value of -0.4 or -5.5 as a result of the angle estimation would be just as plausible as the true value 0.3, ie, a reliable angular estimate is not possible. The reason is that with the planar antenna with the antenna elements 18 ' in 4 the condition has been violated that the distance between the antenna elements is maximum λ / 2.

For the antenna elements 18 Although this condition is also violated by the compliant antenna, the angle density spectrum is shown here by the curve 44 in 8th is a clear maximum at about 0.3. This means that with the compliant antenna an angle estimation under these conditions is still possible and also provides a reasonably correct result. With a planar antenna, this result could only be obtained if, with the same aperture, the number of antenna elements 18 ' would be increased so that the distances between the individual antenna elements are smaller. Since the signals of each antenna element must be evaluated separately, this would require a much greater effort in the evaluation of the signals.

The compliant antenna according to the invention thus not only allows a larger field of view (as indicated by the widely scattered directional characteristics in FIG 6 illustrated), but also greater angular estimation accuracy.

Another advantage of the conformal antenna is that the angular resolution is largely independent of the position of the object in the field of view, while in a planar antenna, the angular resolution decreases significantly towards the edges of the field of view.

In general, with an antenna array, the blur Δθ in the angle measurement is approximately proportional to the quotient of the wavelength λ and the projection d of the aperture of the antenna array on the plane perpendicular to the direction of incidence of the radar radiation. Approximately: $$\mathrm{\Delta \theta }=0.64*\left(\mathrm{\lambda }\text{/ d}\right)\text{,}$$

In 9 is schematically a planar antenna array with antenna elements 18 ' which has the aperture d 'in the plane of the array. However, if the radar radiation is incident not perpendicular to the plane of the array but at an angle α, the projection d of the aperture is given by: $$\text{d}=\text{d '}*\text{cos}\left(\mathrm{\alpha }\right)\text{,}$$

As 9 shows, the projected aperture d decreases sharply with increasing angle α, so that the blur in the angle measurement becomes larger and, correspondingly, the angular resolution becomes poorer.

In the case of a conforming antenna, on the other hand, even with a large angle of incidence α, that is to say with an object near the edge of the visual field, a considerable part of the radar radiation falls on a zone of the array in which the surface of the antenna substrate 16 approximately at right angles to the direction of incidence of the radiation. When the angle of incidence α varies, only the zone on the surface of the antenna substrate shifts, which is perpendicular to the direction of incidence, but the relative size of this zone remains approximately the same, so that the projected aperture changes significantly less. This angular independence of the angular resolution significantly simplifies the signal evaluation and further improves the accuracy of the angular estimation.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013008953 A1 [0003]
• DE 102014208389 A1 [0004]

Claims (5)

Radar sensor arrangement on a motor vehicle (10) having at least two angle-resolving radar sensors (12) forming together with a control and evaluation device (14) a cooperative radar system, characterized, in that the radar sensors (12) are each a group antenna with a in the direction of Angular resolution curved aperture surface (16) have. Radar sensor according to Claim 1 in which the curved antenna substrates (16) of the radar sensors are each adapted to a curved shape of a body part of the motor vehicle (10). Radar sensor according to Claim 1 or 2 in which at least two radar sensors (12) are arranged in corners of the vehicle body. Radar sensor arrangement according to one of the preceding claims, in which all radar sensors (12) together cover a field of view of 360 °. A radar sensor assembly as claimed in any one of the preceding claims, wherein antenna elements (18) of the array antenna of each radar sensor (12) are disposed on the curved aperture surface (16) to provide a uniform angular estimation accuracy throughout the field of view (24) of the radar sensor.

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