WO2008028739A1

WO2008028739A1 - Antenna arrangement with parasitically coupled antenna elements

Info

Publication number: WO2008028739A1
Application number: PCT/EP2007/058228
Authority: WO
Inventors: Thomas Hansen; Martin Schneider; Joerg Schoebel; Oliver Brueggemann
Original assignee: Robert Bosch Gmbh
Priority date: 2006-09-07
Filing date: 2007-08-08
Publication date: 2008-03-13
Also published as: DE102006041982A1

Abstract

In the case of an antenna arrangement having at least one primary antenna element (10), in particular in the form of a planar antenna element, parasitic antenna elements (11) are arranged in the azimuth and/or elevation direction parallel to the primary antenna element or elements (10) in order to broaden the beam lobe of the at least one primary antenna element (10), with this at least one further parasitic antenna element being coupled, just by electromagnetic field coupling, to the primary antenna element (10), at a minimum distance which is approximately equal to half the free-space wavelength.

Description

description

title

ANTENNA ARRANGEMENT WITH PARASITIC ANCHORED ANTENNA ELEMENTS

State of the art

The invention is based on an antenna arrangement with at least one primary radiator.

For some years now, the field of driver assistance functions with forward-looking

Detection systems Radar sensors in use, which operate primarily in the frequency range 76 to 77 GHz. These are still used in the upper class segment for the realization of the assistance function "adaptive cruise control" (ACC) in the speed range 50 to 180 km / h. At the further development of the systems towards a use also in the lower speed range, z. B. for

Realization of an automatic stall sequence procedure is currently in progress, or the function "braking to a standstill" (without restarting) .In the future, radar sensors will also be used for other comfort and safety functions, such as blind spot monitoring, reversing and parking assistance or "precrash". - Functions (triggering of reversible restraint systems, arming of airbags, etc., preconditioning of the

Brake system, automatic emergency brake), etc. find use [I].

Typically, 77GHz first and second generation radar sensors operate with lens antennas. Via several feed antennas, which are located in the focal plane of the lens, a plurality of partially overlapping beam lobes are formed (analog

Beam shaping). This principle is illustrated in FIG. 1. The azimuthal angular position of the target object is determined on the basis of the signal amplitudes and / or phases in the individual beam lobes. Characteristic of lens antennas are the relatively large depth of a few centimeters, which results from the required distance of the feed antennas (in the focal plane) of the lens. A radar system can also be realized in a planar structure with planar antennas, so that the depth is significantly reduced. 77 GHz frontend with digital beamforming and based on planar radiators (patch antennas) are known from [2]. The publications [1, 4, 5, 6, 7] also describe such systems.

Planar antennas in automotive radar sensors are commonly constructed as array antennas [1, 4, 5, 6, 7]. In elevation, series-fed antenna columns are used, with which beam shaping is performed in azimuth. The basic structure of such an antenna is sketched in FIG.

Advantages of the invention

With the measures of claim 1, d. H. with parasitically coupled antenna elements in addition to at least one powered antenna element in a minimum distance which is approximately equal to half the free space wavelength, can be

Affect radiation of the antenna arrangement so that a broadening of the beam lobe can be achieved. As antenna elements, both individual radiators, as well as groups of individual radiators can be used. This leads to the following advantages:

- The characteristic of the antenna is widened compared to the single radiator, there is no additional space for a power divider needed only very small losses occur.

This actually results in an increase in the antenna gain in the edge region (at the expense of the center) and the characteristic approaches a rectangular characteristic (with a power divider with corresponding losses may indeed be a

Widening of the antenna characteristic can be achieved by the losses of the gain in the edge region but is typically not significantly greater than for the single element) the avoidance of ohmic losses (and radiation losses) in a power divider is particularly favorable at high frequencies, eg. In the

Millimeter wave range there are no sidelobes and associated zeros or minima in the

Beam characteristic on.

In the dependent claims further advantageous embodiments are shown. drawings

With reference to the drawings, embodiments of the invention will be explained.

Show it

FIG. 1 shows the formation of a plurality of beam lobes by a plurality of feeds in a lens antenna,

Figure 2 shows the basic structure of a typical array antenna for automotive radar, Figure 3 a to d, the basic arrangement of parasitic antenna elements with a. a primary radiator b. a more parasitic antenna element in elevation, c. a parasitic antenna element on each side of the primary radiator in azimuth, d. a parasitic antenna element in elevation and two parasitic antenna elements symmetrical in azimuth, wherein the distance of the outer elements is about twice as large as that of the inner elements,

Figure 4a shows the basic structure of an antenna column with series feed, Figure 4b shows the basic structure of an antenna column with parallel feed, Figure 5a, b is a primary radiator and parasitic antenna elements as columns with series feed, wherein in Figure 5a conclusions of the parasitic columns with end elements and in FIG FIG. 7 shows a plan view of an antenna arrangement with slot-coupled patches, FIG perpendicular to the antenna elements,

FIG. 9 Measurement results of the antenna gain over the azimuth.

Description of exemplary embodiments

For the realization of planar antennas usually planar RF lines, such as

Microstrip, coplanar, slot lines, etc. used. In addition, the following modifications can occur: a metallization of the underside of the substrate, multilayer substrates, wherein metallic layers can also occur - dielectric layers that cover the metallic interconnects. - A -

AIs substrate serve special microwave substrates, eg. As plastic, which may be reinforced with glass fibers or mixed with fillers, ceramics, glass, etc.

On the microwave substrate, planar antennas, for example, patch, stub,

Slot or Dipolstrahlern constructed. Examples are found e.g. in [3]. To increase the bandwidth and radiator elements consisting of coupled individual elements such. B. juxtaposed patches or in several substrate layers stacked patches used. For the coupling of these radiator elements to the power supply, there are various concepts, such as direct coupling, capacitive coupling, aperture or slot coupling or coupling via electrical feedthroughs.

The most important configurations of the feed are the series feed [3] and the parallel, usually in-phase feed ("corporate feed") .The power distribution network is located either on the same metal level as the antenna elements or on the substrate side opposite the antenna elements The substrate may have an internal, locally interrupted metallization, or it may be composed of a plurality of dielectric layers, and the power distribution and supply may be effected on an inner substrate layer.

The main lobe of the radar antenna of an automotive radar sensor is designed in azimuth so that the transmission signal is irradiated for the application sufficient angular range. For medium to long-range applications (typical ACC), an angle range of ± 4 ° to ± 8 ° is generally sufficient to irradiate multiple lanes of the road, especially the highway, even at typical curve radii.

In the radar sensor according to FIG. 1, the same beam lobes are used for transmission as for the reception (monostatic system), with all beam lobes being emitted simultaneously, so that the resulting beam characteristic corresponds to the sum of the beam lobes, taking into account the phases of the individual beam lobes.

The radar sensor according to [2] uses a separate transmitting antenna (bistatic system). The azimuthal angular range covered by the sensor is ± 10 °. For applications that rely on short-range radar sensor technology, SRR, this becomes even more important larger azimuthal detection range required. In [1] is called an order of + 60 °.

In order to achieve a beam lobe as wide as possible in azimuth, an antenna column is usually used, consisting of individual elements 1, 3 arranged one above the other in elevation, as transmission antenna Tx a single antenna column of patch elements is sketched. Thus, however, a 3dB width of the beam lobe in azimuth in the order of ± 60 ° is not feasible, depending on the direction of polarization are the 3dB widths of the beam lobe simple patch elements at about ± 52 ° (E-plane) and about ± 41 ° (H-plane). The latter value applies to the usually used direct series feed (see Figure 6). When using stacked patches to increase the bandwidth, the beam lobe usually becomes narrower.

If one arranges several antenna columns side by side, normally the beam lobe becomes narrower in azimuth because of the enlargement of the aperture. With the help of certain

Amplitude and phase assignments of the antenna columns but also a broadening of the beam lobe can be achieved. However, this approach has the disadvantage that, first, space must be provided for a corresponding power divider (compare FIG. 2) and, secondly, additional losses occur in the power divider. Third, sidelobes can occur. In particular, the zeros (or minima) associated with the sidelobes in the

Antenna characteristics are not acceptable in the illumination range of the radar sensor.

In contrast, in the invention, to widen the beam lobe of the at least one primary radiator 10 in the azimuth and / or elevation plane, at least one further parasitic, in particular likewise planar, antenna element Hin of the azimuth and / or

Elevation direction arranged parallel to the / the primary radiator / n 10, wherein said at least one further antenna element 11 is coupled only parasitically by electromagnetic field coupling to the primary radiator 10 in a minimum distance which is approximately equal to half the free space wavelength.

Although parasitically coupled antenna elements in the form of patch elements for increasing the bandwidth are known [8], [9]. In this case, a relatively strong coupling of the elements is used to increase the bandwidth of the arrangement. This is reflected in the ratio of the distance of the elements to their dimensions: the slot width between the elements is much smaller than the dimensions of the elements. In contrast, the Distance of the parasitic elements in the invention approximately equal to half the free space wavelength. With conventional microwave structures (the electricity number of 3 and above), this results in a slot width on the order of the element dimensions, which is thus considerably larger than the slot width in [8], [9].

The 3dB beam lobe widths depicted in [8] and [9] are significantly smaller than the beam lobe widths obtainable in the invention. The elements described in [8] and [9] thus do not cause any significant broadening of the beam lobe.

In [10] parasitically coupled elements are used to increase the directivity of a group antenna, i. H. make the beam lobe narrower.

FIG. 3 shows, by way of example, the arrangement according to the invention of parasitic antenna elements (FIG. 3a) on a primary radiator 10 with feed 40 in elevation (FIG. 3b) or in azimuth (FIG. 3c) with distances dl between primary radiator and parasitic elements

Antenna elements and as a combination (Figure 3d) with a parasitic antenna element in elevation E and two parasitic antenna elements symmetrically in azimuth A, wherein the distance d2 of the outer antenna elements is about twice as large as that of the inner.

Planar antennas in automotive radar sensors are commonly constructed in microstrip line technology. A single- or multi-layered microwave substrate is coated on both sides with metal. At least one of the two metal layers is structured and forms the signal line plane. In the signal line plane, the feeder lines 20 of the antenna columns and optionally the transceiver modules (or parts thereof) are arranged. The other metal level is the ground level. Below the ground plane further substrate and metal layers can be arranged, in which z. B. the low frequency / baseband and digital electronics for processing the low frequency / baseband signals and for driving and (digital) signal processing are constructed. In combination with it, even more microwave substrate levels can be used on which optionally z. B. the transmitting and receiving modules are constructed. Above the

Signal line level may be further substrate and metal levels, on which z. B. multiple antenna patches are stacked to increase the bandwidth or the planes with slot radiators or coupling slots 31 and (slot-coupled) patches are (see Fig. Figure 7a). Figure 4 shows schematically the structure of an antenna column 1 with series feed and an antenna column 2 with parallel feed. In the signal line level mentioned, the feed lines 20 of the antenna columns are arranged. These are usually designed as microstrip lines, wherein several sections with different impedances can occur for adaptation.

To the feed line 20, the antenna radiator elements 50 are coupled. This can in the simplest case by direct coupling 30 in series connection to the feed line or z. B. via leads, feedthroughs or via capacitive coupling can be realized. Other possibilities are the coupling of the radiator element via the electromagnetic field in the form of a Schlitzkopplung- or the slots are used directly as a radiator.

As radiator elements serve z. As patches stubs, the poles, slots or groups of individual elements. At the end of column 1, an element 50a can be used which radiates all incident power so that no reflection occurs.

FIG. 5 illustrates the use in groups with series feed. As a primary radiator and parasitic antenna elements 50 series-fed groups of individual radiators are used. An exemplary realization of the concept according to FIG. 5a is shown in FIG. 6. The spotlights used are directly fed patch elements 50.

FIG. 7 a, b shows a realization with slot-coupled patches 50, wherein the coupling takes place via the coupling slot 31. The feed 20 is in a plane parallel to the antenna elements behind the plane of the primary emitters and parasitic antenna elements 50. Figure 8 shows a structure in which the feed 20 is in a plane perpendicular to the antenna elements.

FIG. 9 shows measurement results of the antenna gain over the azimuthal angle. The following antennas were constructed and characterized:

I. A series-fed individual column 1 according to FIG. 4 in a realization with directly fed patch elements (see FIG.

IL An equally constructed column, which in each case additionally has on both sides a symmetrically arranged parasitic column (structure in FIG. 6). It can be seen that the beam characteristic of the individual gaps can be considerably widened by the parasitic gaps, with only very small losses occurring. With a power divider could also achieve a broadening of the beam lobe, but at the cost of significantly greater losses. For angles larger than approx. ± 35 °, the gain increases by approx. 2 dB. Thus, there is practically an increase in the antenna characteristic in the edge region and this at the expense of the gain in the middle angle range, bringing the antenna pattern closer to a rectangular characteristic. Furthermore, no side lobes occur and, associated therewith, no zeros in the antenna diagram.

references

[I] R. Mende, H. Rohling, New Automotive Applications for Smart Radar Systems, Proc.

German Radar Symposium 2002, German Society for Positioning and Navigation (2002), 35-40.

[2] A. Kawakubo, S. Tokoro, Y. Yamada, K. Kuroda, T. Kawasaki, Electronically Scanning

Millimeter Wave Radar for Forward Objects Detection, SAE Technical Paper 2004-01-1122.

[3] P. Bhartia, K.V.S. Rao, R.S. Tomar, Millimeter Wave Microstrip and Printed Circuit

Antennas, Artech House, Boston, London 1991. [4] DE-19951123 C2.

[5] Mark E. Russel, Arthur Crain, Anthony Curran, Richard A. Campbell, Clifford A. Drubin, and William F. Miccioli; Millimeter Wave Radar Sensor for Automotive Intelligent Cruise

Control (ICC), IEEE Transactions on Microwave Theory and Techniques, Vol. 12

December 1997, 2444-2453. [6] Y. Asano, Electrically Scanned Millimeter Wave Radar for Automotive Applications, IEEE

MTT-S International Microwave Symposium IMS 2002, Workshop on Automotive Radar and

Prospective Circuit / Antenna Technologies - From Car Collision Avoidance to Autonomous

Driving (WMA).

[7] brochure "Safety at your Fingertips: new, highly integrated, very accurate automotive radar sensors for collision warning and parking assistance", MTS Microwave Technology and

Sensors GmbH, Ottobrunn.

[8] G. Kumar, K.C. Gupta, Nonradiating Edges and Four Edges Gap-Coupled Multiple

Resonator Broad-Band Microstrip Antennas, IEEE Trans. Antennas Propagate. AP-33 (1985),

173-178. [9] CK. Aanandan, P. Mohanan, K.G. Nair, Broad Band Gap Coupled Microstrip Antenna,

IEEE Trans. Antennas Propagate. 38 (1990), 1581-1586.

[10] A.A. Bokhari, H.K. Smith, J.R: Mosig, J.F: Zurich, F.E. Gardiol, Superdirective Antenna

Array of Printed Parasitic Elements, Electronics Letters 28 (1992), 1332-1334.

Claims

claims

1. Antenna arrangement with at least one primary radiator (10), in particular in the form of a planar antenna element, wherein for broadening the beam lobe of the at least one primary radiator (10) at least one further parasitic, in particular likewise planar antenna element (11) in the azimuth and / or

Elevation direction is arranged parallel to the / the Primärstrahler / n (10) and wherein said at least one further antenna element (11) only parasitically coupled by electromagnetic field coupling to the primary radiator (10) at a minimum distance which is approximately equal to half the free space wavelength.

2. Antenna arrangement according to claim 1, characterized in that the at least one parasitic element (11) at a distance of about half a free space wavelength and the use of multiple parasitic antenna elements at a distance of multiples of about half a free space wavelength of the primary radiator / the primary radiators ( 10).

3. Antenna arrangement according to claim 1 or 2, characterized in that in each case exactly one parasitic antenna element (11) is located on both sides of the primary radiator (10) in the corresponding direction.

4. Antenna arrangement according to claim 1 or 2, characterized in that on both sides of the primary radiator (10) in the corresponding direction in each case two parasitic elements (11) are located, wherein the second parasitic element approximately twice the distance of the first parasitic antenna element of the has at least one primary radiator (10).

5. Antenna arrangement according to one of claims 1 to 4, characterized in that the parasitic elements (11) in the respective direction are arranged symmetrically about the primary radiator (10).

6. Antenna arrangement according to one of claims 1 to 5, characterized in that as primary radiator (10) or as parasitic antenna elements (11, 50) groups of individual antenna radiators are used, which are connected via one or more feeds (21).

7. Antenna arrangement according to claim 6, characterized in that the feeds (21) of the groups are designed as series feeds.

8. Antenna arrangement according to claim 7, characterized in that the parasitic antenna elements (50) are formed by series-fed groups which are connected to a

Are finished at the end or at both ends reflection-poor.

9. Antenna arrangement according to claim 8, characterized in that the termination by a parasitic antenna element (50a) takes place, which emits most of the injected high-frequency power.

10. Antenna arrangement according to claim 8, characterized in that the termination is effected by a terminating resistor.

11. Antenna arrangement according to claim 10, characterized in that the

Terminating resistor is connected by a radial stub or by a high-frequency feedthrough to the ground plane of the substrate carrying the antenna elements.

12. Antenna arrangement according to claim 8, characterized in that the conclusion is realized by attachment of absorber material on the feed line.

13. Antenna arrangement according to one of claims 1 to 12, characterized in that the feed of the primary radiator (10) is located in a plane which is parallel and with respect to the main beam direction behind the plane of the primary radiator and parasitic antenna elements.

14. Antenna arrangement according to one of claims 1 to 12, characterized in that the feed of the primary radiator is located in a plane which is perpendicular to the plane of the primary radiator and parasitic antenna elements.

15. Antenna arrangement according to one of claims 1 to 14, characterized in that as antenna elements for both the primary radiator (10) and / or the parasitic antenna elements (11) the following types of planar radiators are used: planar patch elements, planar stub elements or planar dipole elements, coupled patch elements consisting of two or more patch elements arranged one above the other or next to one another. Slits in a metallization plane.

16. Antenna arrangement according to claim 15, characterized in that the primary radiator and parasitic antenna elements are connected directly or via lines to a feed.

17. Antenna arrangement according to claim 15, characterized in that the

Antenna elements of the primary radiator (10) and parasitic antenna elements (11) via electromagnetic coupling, z. B. slot coupling are connected to a power supply.

18. Antenna arrangement according to one of claims 1 to 17 for use in a

Automotive radar sensor.