Antenna array for a radar sensor

Abstract

An antenna array for a radar sensor, having an antenna designed as a group antenna and operable as a transmit antenna and having an antenna configuration operable as a receive antenna, wherein the array has, in addition to the first antenna designed as a group antenna, a second antenna operable as a transmit antenna that has a smaller aperture than the first antenna, and the first and second antenna are designed for the transmission of radar waves having polarization orthogonal to one another, and the antenna configuration operable as a receive antenna is sensitive to both directions of polarization.

Claims

1. An antenna array for a radar sensor, comprising: a first antenna, which is configured as a planar group antenna having a plurality of parallel antenna columns, and which is operable as a transmit antenna; an antenna configuration, which is operable as a receive antenna; and a second antenna, which is operable as a transmit antenna that has a smaller aperture than the first antenna, wherein the first antenna and second antenna are configured to transmit radar waves having polarization orthogonal to one another, wherein the plurality of antenna columns includes groups of the antenna columns, each of the groups having fewer of the antenna columns than the plurality of antenna columns, wherein there is a gap between the groups and wherein the gap is filled by the second antenna; wherein the antenna configuration, which is operable as the receive antenna is sensitive to both directions of polarization.

2. The antenna array as recited in claim 1, wherein the second antenna has a smaller aperture in azimuth than the first antenna.

3. The antenna array as recited in claim 1, wherein the first antenna and the second antenna have a common phase source point.

4. The antenna array as recited in claim 1, wherein the first antenna has a plurality of antenna columns having a plurality of antenna patches, wherein the second antenna has at least one antenna column having a plurality of antenna patches, and wherein the number of antenna columns of the second antenna is smaller than that of the first antenna.

5. The antenna array as recited in claim 4, wherein the antenna patches of the first antenna are shaped such that they emit radar waves whose polarization direction is parallel to a longitudinal direction of the antenna columns of the first antenna, and wherein the second antenna has antenna patches that are shaped such that they emit radar waves whose polarization direction is at a right angle to a longitudinal direction of the antenna column of the second antenna.

6. The antenna array as recited in claim 1, wherein the first antenna and the second antenna are part of the antenna configuration, which is operable as the receive antenna.

7. The antenna array as recited in claim 6, wherein the first antenna and the second antenna are fed from a common feed network, and which, as receive antennas, supply a uniform receive signal.

8. The antenna array as recited in claim 1, wherein the antenna configuration, which is operable as the receive antenna has at least two antennas, which are different from the first antenna and the second antenna, and which are each selectively sensitive to one of the two polarization directions.

9. A radar sensor for motor vehicles, comprising: an antenna array for the radar sensor, including: a first antenna, which is configured as a planar group antenna having a plurality of parallel antenna columns, and which is operable as a transmit antenna; an antenna configuration, which is operable as a receive antenna; and a second antenna, which is operable as a transmit antenna and which has a smaller aperture than the first antenna, wherein the first antenna and second antenna are configured to transmit radar waves having polarization orthogonal to one another, wherein the plurality of antenna columns includes groups of the antenna columns, each of the groups having fewer of the antenna columns than the plurality of antenna columns, wherein there is a gap between the groups and wherein the gap is filled by the second antenna; wherein the antenna configuration, which is operable as the receive antenna is sensitive to both directions of polarization.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example of an antenna array according to the present invention.

(2) FIG. 2 shows a directional characteristic of the antenna array of FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(3) The example antenna array shown in FIG. 1 has a first antenna 10 in the form of a planar group antenna having six parallel antenna columns 12. The six antenna columns 12 are divided into two groups each having three columns, between which there is a gap that is filled by a second antenna 14.

(4) The six columns of first antenna 10 and the individual columns of second antenna 14 are fed serially by a common feed network 16 with a radio-frequency signal having wavelength A. The connection points of all seven antenna columns to feed network 16 are situated at uniform distances that correspond to wavelength A, so that all antenna columns obtain signals having the same phase. The connection point of the single-column antenna 14 is situated centrically between the connection points of antenna columns 12, and first antenna 10 and second antenna 14 have a common phase source point 18.

(5) Each antenna column 12 of the first antenna is made up, in the depicted example, of five antenna patches 20 tapered in the vertical direction (or optionally also, or only, in the horizontal direction), each having height λ/2. First antenna 10 thus emits radar radiation polarized in a first polarization direction z.

(6) As an example, it can be assumed that the antenna array is formed on a circuit board of a radar sensor that is installed in a motor vehicle in such a way that the circuit board, and thus the plane of antennas 10, 14, is oriented vertically, and the normal to this plane runs parallel to the longitudinal axis of the vehicle. The radar radiation of the first antenna 10 is then thus polarized vertically, and, due to the large aperture of antenna 10 in the azimuth, the radiation is sharply focused in the horizontal direction.

(7) However, second antenna 14, formed by an individual column, has ten patches 22 that go out at a right angle from the associated feed line (alternating in opposite directions), and thus emit radar radiation that is linearly polarized in linear fashion in a second polarization direction y at a right angle to first polarization direction z. Because the aperture of second antenna 14 in the azimuth is only about 1/7 of the aperture of first antenna 10, the radiation emitted by second antenna 14 in the azimuth is relatively widely fanned out, so that—with a smaller range—a significantly larger angular region is covered than with the radar radiation of first antenna 10.

(8) As an example, it can be assumed that first antenna 10 and second antenna 14, in the radar sensor considered here, have both the function of transmit antennas and the function of receive antennas. The received radar echo is then coupled out, in a conventional manner, using a coupler connected to feed network 16, and is separated from the transmit signal, so that from the two antennas 10, 12 together one obtains only a single receive signal in a single evaluation channel.

(9) FIG. 2 graphically shows the directional characteristic of the antenna array shown in FIG. 1. This directional characteristic indicates the antenna gain G as a function of the azimuth angle θ. It will be seen that the gain has a maximum at azimuth angle 0°, flanked by minima at approximately ±30°, but overall has only relatively small fluctuations. If the directional characteristic of first antenna 10 is instead regarded by itself, then there would be significantly more pronounced minima at approximately ±30°, so that practically no signal would then be detectable from objects situated at these angles. These gaps are filled by the signal of second antenna 14. Thus, the present invention enables a reliable location of objects over a very large azimuth angle range, the sensitivity being only slightly lower even in the vicinity of the minima at ±30°.

(10) In another specific example embodiment, a bistatic antenna design can also be realized in which the antenna array shown in FIG. 1 is present at least twice, once as a transmit antenna and once as a receive antenna.

(11) In addition, an antenna array would also be possible in which the array shown in FIG. 1 having antennas 10 and 14 is used as a transmit antenna, and two separate receive antennas are provided for the reception of the radar signals, of which one is sensitive exclusively to vertical polarization direction z and the other is sensitive exclusively to horizontal polarization direction y. In this case, the different polarized radar echoes can be evaluated separately in two receive channels, the one receive channel corresponding to a long-range sensor and the other receive channel corresponding to a near-range sensor.