The present invention relates to a bistatic array antenna having a focusing arrangement for beam focusing, and a method for operating such an antenna.
A radar sensor having digital beam shaping requires large antenna arrays, particularly if narrow beams are required such as in long range radar. This conflicts with the desire to manufacture a sensor that is as small in surface area as possible, however. Alternatively, a (cylindrical) lens may be used, which results in a narrowing of the beams in one plane (elevation) and reduces the number of antenna elements in elevation, for example as described in PCT Application No. WO 2006/048352 A2. This does not change the geometric dimensions in the azimuth direction however.
Another alternative is a monostatic radar system, in which the same antenna is used for transmitting and receiving, for example as described in PCT Application No. WO 2006/029926A1. However, this means that transmitting and receiving characteristics cannot be selected independently of each other.
Using a bistatic array antenna in accordance with the present invention, in which a focusing arrangement for beam focusing in preferred directions of the array antenna is developed and situated in such a way that beam focusing occurs both in a first preferred direction for the array elements of the transmit mode as well as in another preferred direction for the array elements of the receive mode, it is possible to achieve beam focusing at a very low surface area requirement, in particular in elevation, using separate array elements for the transmit mode and the receive mode.
Furthermore, in a development according to an example embodiment of the present invention, it is possible to achieve digital beam shaping having narrow radiation lobes and angle estimations, particularly in the azimuth direction, likewise with a very low surface area requirement.
When using a focusing arrangement in the form of a bifocal lens, in particular a bifocal cylindrical lens, beam focusing is achieved in a plane, in which no digital beam shaping occurs, preferably in elevation. The beam focusing in preferred directions for elevation may thus be adjusted in an optimized manner and independently of the azimuth separated according to the array elements for the transmit mode and the receive mode.
The array elements are preferably situated across from the focusing arrangement/the bifocal cylindrical lens in such a way that the phase source point of the array elements for the receive mode and for the transmit mode is located respectively in one focal point of the focusing arrangement/the bifocal lens. As a consequence, the array elements for the receive mode and for the transmit mode may be arranged separated in elevation one above the other instead of side by side as in conventional design approaches. This results in a substantially lower surface area requirement. The beam focusing occurs preferably in elevation by array elements on a substrate and the focusing arrangement/bifocal lens and in azimuth only by the array elements on the substrate. The entire base width of the antenna array is available for beam focusing/digital beam shaping in the azimuth and thus allows for wide beam swinging in the azimuth in transmit mode and for a reliable evaluation in receive mode.
Patch elements, slot elements or patch elements having a polyrod on a substrate may be used alternatively as array elements. In elevation, multiple array elements or rows of array elements may be used to ensure an optimized side lobe attenuation.
Specific embodiments of the present invention are explained in greater detail below with reference to the figures.
The present invention provides a focusing arrangement/device for beam focusing in two preferred directions of a radar array antenna for bistatic operation, i.e., different array elements are provided for a transmit mode than for a receive mode. The focusing arrangement effects beam focusing in a first preferred direction of the elevation for the transmit mode and beam focusing in another second preferred direction of the elevation for the receive mode. Below, a bifocal lens is described as a focusing arrangement/device, in particular, a bifocal cylindrical lens having two different focal points. Instead of such a bifocal cylindrical lens, suitable grid structures of other dielectric structures may be used as well, which likewise have two focal points or focal lines.
In an evaluation device 8, the different mixed received signals (intermediate frequency signals) of mixing devices 7 are sampled in a time-synchronous manner (digitized) and subjected to a conventional digital beam shaping (DBF, digital beam forming). Because of the fixed phase and amplitude relation of the individual received signals in azimuth, it is possible to extract both the distance and also the angle information of radar targets.
In front of the plane of substrate 4, on which array elements 1 and 2 are situated, a bifocal cylindrical lens 9 is disposed, which is shown in cross section in
If, as shown in
Number | Date | Country | Kind |
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10 2007 058 236.8 | Dec 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP08/63735 | 10/13/2008 | WO | 00 | 6/3/2010 |