Patent Publication Number: US-6215444-B1

Title: Array antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority is claimed with respect to German Application No. 198 31 877.4 filed in Germany on Jul. 17, 1999, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to an array antenna with at least one array of multiple aerials with several planar microwave resonators in strip transmission line technique, which are connected to each other with micro strip transmission line segments. 
     Known antennas of this type contain features which are not adequate for many purposes, that is with respect to the antenna characteristic and increased undesirable radiation if T-junctions are present. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to specify an array antenna of the aforementioned type, which has an improved antenna characteristic with reduced, undesirable radiation. 
     The above and other objects are accomplished according to the invention by the provision of an array antenna, comprising at least one array of multiple aerials with several planar microwave resonators in strip transmission line technique, which are connected to each other with micro strip transmission line segments, wherein a preferably rectangular window is provided underneath one of the microwave resonators for feeding an array of multiple aerials, which window is located in the rear metal-coating of the substrate, is covered completely by the resonator above and connects the resonator with a connecting line below the window. 
    
    
     Advantageous embodiments and modifications of the invention follow from the following detailed disclosure considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of an array antenna according to one embodiment of the invention. 
     FIGS. 2 and 3 are diagrams showing antenna characteristics of an array of multiple aerials having the design as shown in FIG.  1 . 
     FIG. 4 is a schematic showing an array antenna composed of a plurality of different arrays with multiple aerials of the type shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An array of multiple aerials preferably comprises three resonators. However, it is advantageous if an array of multiple aerials comprises seven resonators. Particularly favorable qualities are exhibited by arrays with multiple aerials, W for which a first resonator R 1  is located directly above the window KS and preferably extends past the window in longitudinal and lateral direction and the remaining resonators R 2 -R 7  are distributed evenly, in particular in a circle around the centrally arranged first resonator R 1  and are connected to the first resonator by separate connecting lines VL. 
     Arrangements with a mirror symmetry with respect to at least one, preferably two, crossed mirror planes that extend perpendicular to the substrate plane are advantageous. The several resonators preferably oscillate with the same phase and preferably have the same polarization. 
     By arranging the window K- 5  below the metal-coated surface of one of the resonators R 1  in the array of multiple aerials, the coupling to the connecting or feed line does not cause a direct radiation, e.g. as is the case when coupling into a microstrip transmission line. It is preferable if the power distribution occurs advantageously without complicated power network with discontinuity (particularly T-junctions). As a result, the power distribution is less sensitive to a higher substrate thickness. In addition, transmission line lengths are minimized, so that there are fewer line losses on the whole. 
     With respect to the substrate plane, the array antenna according to the invention has less pronounced directional dependencies as compared to a classic microstrip array of multiple aerials. There is less coupling of antenna elements than for the known designs, since the radiating edges of the individual resonator surfaces (patches) can be at greater distances. 
     FIG. 1 shows a particularly advantageous array of 7 radiator elements (resonators), for which the remaining resonators are arranged with uniform angular distribution around a centrally arranged first resonator R 1 , in a circle around this central resonator. In each case, two neighboring resonators have the same distances between the center points of the resonator surfaces. The surface distribution of the array antenna here can be divided into a uniform honeycomb pattern, sketched by auxiliary lines with breaks as in FIG. 1, with resonator surfaces that are respectively arranged in the center of the individual honeycomb cells. In the metal-coated surface of the first resonator R 1 , which is closed in the real case, the window KS underneath it is indicated in the back of the metal coating. The additional resonators R 2  to R 7 , which surround the central resonator R 1 , are each directly connected to the central resonator via a microstrip transmission line VL. The lengths of the transmission lines VL are selected such that all resonators R 1  to R 7  oscillate with the same phase. 
     FIG. 2 represents a section through the E-plane of the antenna and shows a typical characteristic of an array of multiple aerials, having the design as sketched in FIG.  1 . 
     FIG. 3 shows a radiation characteristic for such an array of multiple aerials, in a plane that is tilted at a 30° angle to the E plane. The antenna patterns show a high concentration in the main lobe of the antenna pattern and a strong damping in the secondary lobe. 
     FIG. 4 shows an array antenna,  1  composed of a plurality of different arrays with multiple aerials, W of the type as sketched in FIG. 1, which are combined to form a regular arrangement. The array antenna  1  sketched for the concrete case consists, for example, of 91 arrays of multiple aerials with uniform design. The individual arrays of multiple aerials, W having respectively 7 radiator elements (resonators), in this case are coupled by way of a low-loss conductive network on the back of the antenna, via windows in the rear metal-coating, particularly a waveguide network with windows. Without any aperture occupancy, the antenna shows a slight half intensity width of less than 3° and a secondary lobe damping of more than 16 db. 
     The invention is not limited to the above-described exemplary embodiments, but can be changed in various ways within the framework of expert knowledge.