Flat aperture coupled antenna with multilayer structure and radiating patches

(54) (56) (57)

INVENTOR INVENTOR

REPRESENTATIVE TITLE

Allgon AB, Box 500 184 25 Äkersberga SE

Ingela Nyström, Sundbyberg SE, Björn Lindmark, Solna Dan Karlsson, Solna SE

Axel Ehrner's Patent Office AB

Flat antenna

CALLED PUBLICATIONS: - - SUMMARY:

SEE,

A flat, aperture-coupled antenna with a multilayer structure is described. The rear of the antenna comprises a metal reflector device comprising a hollow structure (3, 5) with separate box-shaped compartments, located in the center of radiant patches, corresponding pairs of orthogonal slots and feed elements, whereby microwave propagation within the hollow metal structure is interrupted and the interconnected couplings are interposed. .

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The numbers in brackets indicate international identification code, INID code. Letters in clips indicate International Document Code.

509 749

The present invention relates to a substantially flat, aperture-coupled antenna, comprising single-layer structure having a number of radiating patches arranged on a layer of dielectric material, a corresponding number of apertures, each in the form of two orthogonal slits, in a ground plane layer, and a corresponding number of feeding elements in a feeding network arranged on at least one flat disk for supplying microwave energy from said feeding element via said orthogonal slits to said radiating patches to cause the latter to form a microwave lobe extending from the front of the antenna, the rear side thereof comprising a metal reflector device.

Such flat, aperture-coupled antennas are generally known in various embodiments. See, for example, U.S. Patent Nos. 5,030,961 (Tsao), 5,241,321 (Tsao), 5, 355,143 (Ztircher et al) and the published European patent application with publication number 520908 (Alcatel Espace).

The radiating patches are often arranged in a matrix, i.e. a two-dimensional pattern with rows and columns, so that the antenna is extended over a surface area. Alternatively, the antenna may be provided with radiating patches arranged in a vertical row, optionally adjacent one or more antenna elements to form a multilob antenna unit.

In such an antenna construction with a set or row of radiant patches and a rear reflector device, there is a technical problem in that the reflector device tends to act as waveguide. Thus, resonances and unwanted couplings may occur between the different apertures in the matrix. Accordingly, the desired lobe configuration is adversely affected, especially if dual polarization is utilized. Further, a substantial portion of the microwave energy supplied to the antenna via the above-mentioned supply network can be irradiated by radiation

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509 749 in addition to the forward lobe and by heat absorption in the metal reflector device.

The antenna construction described in the aforementioned document EP 520908 is somewhat different in that it does not include any orthogonal slots serving to isolate the double-polarized carriers and associated signal channels from each other. Furthermore, there is a sandwich structure with upper and lower metal plates with an intermediate, thin, dielectric plate with a supply network. The two metal plates have integral walls which together form cavities or compartments in the region of the corresponding feed element pairs. However, the feed elements are asymmetrically positioned in the respective cavity, and the two polarizations are therefore not completely isolated from each other.

Against this background, the present invention aims to avoid resonances and unwanted couplings within the antenna and to substantially reduce the losses in microwave energy and to provide an antenna that is easy to assemble and operate efficiently. Yet another specific object is to maintain effective isolation between the separate channels obtained by the double-polarized carriers.

These objects are achieved by the metal reflector assembly comprising a flat, hollow metal structure comprising electrically spaced, box-like compartments located opposite to each radiant patch, respective pair of orthogonal slots, and respective feeding elements, each such box-like compartment being delimited between said ground plane layer such as an upper wall surface lower wall portions and side wall portions extending between said upper and lower wall portions; thereby stopping microwave propagation within the hollow metal structure and preventing interconnection between the orthogonal slots.

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The electrically separated, box-like compartments can be designed in different ways in practice. Some practical embodiments are set forth in the dependent claims 2-13 and will be described below.

The invention is explained in more detail below in connection with three embodiments, which are illustrated in the accompanying drawings.

Fig. 1 is a perspective view, in exploded view, of an end portion of an elongate antenna according to a first embodiment of the invention;

Fig. 2 shows a corresponding view of a second embodiment; and

Fig. 3 shows a corresponding view of a third embodiment.

In the drawings, only those components essential for the basic functions of transmitting and receiving communication signals in the microwave range are shown. Thus, most of the required mechanical and electrical details have been omitted from the drawings.

The antenna comprises a multilayer structure. More specifically, in the first embodiment shown in Fig. 1, there are four layers 1, 2, 3 and 4 which are arranged one on top of the other and laid down as a flat package on a bottom unit 5.

All layers 1-4 have substantially the same dimensions in length and width and are fixed at the top of the bottom unit 5 by mechanical means, for example in elongated grooves (not shown) in the bottom unit 5 or by special fasteners or snap elements (not shown).

The first layer 1 is made of dielectric material and is provided with a number of radiating patches 11 arranged in a longitudinal row, preferably with uniform spacing. As is known per se, the patches are made of an electrically conductive material, for example copper or aluminum.

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Further, there are two layers 2 and 4, also made of dielectric material, which are provided with an upper part and a lower part of a supply network comprising upper supply elements arranged in pairs 21a, 21b, which are connected in pairs to a common supply line 22 in the form of a conductive strip, and lower feed elements 41a and 41b, which are likewise connected in pairs to a common feed strip 42 on the lower layer 4.

Between layers 2 and 4 lies a ground plane layer 3 of conductive material, e.g. copper or aluminum, provided with a series of apertures in the form of intersecting, mutually perpendicular slots 31a, 31b, each pair of orthogonal slots located adjacent to a corresponding radiant patch 11 and a pair of feed elements 21a, 41a, respectively. 21b, 41b.

Microwave energy is supplied through the conductive strips 22 and 42 to the various feed elements 21a, 41a, 21b, 41b, and a significant portion of this energy is transmitted or coupled via the orthogonal slots to the row of patches 11, from which a double-polarized microwave beam is emitted in a well-defined lobe. from the front of the antenna (upwards in Fig. 1). Normally, such a lobe has a limited half-power lobe width of 50-100 ° in a transverse plane to the antenna's longitudinal direction. The longitudinal lobe width is determined by the size of the group antenna, in particular the length of the elongated antenna. By placing a number of similar antennas side by side, oriented with their longitudinal axes vertically, a multilob antenna unit can be formed.

In accordance with the present invention, the bottom unit 5, together with the ground plane layer 3, forms a hollow metal structure with electrically spaced, box-shaped compartments. The hollow metal structure comprises the ground plane layer 3 as the upper wall, the rear metal wall 51 as the lower wall and two side walls.

52, 53. Conveniently, the base unit 5 with the walls 51, 52 and 53 is made of aluminum.

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The inner space within the hollow metal structure 3, 5 serves to accommodate the conductive strips 42 and any other antenna components (such components are not shown in Fig. 1).

In order to prevent the formation of standing waves or other types of microwave propagation in the longitudinal direction within the hollow metal structure 3, 5, a number of transverse partitions 54 are arranged at regular distances along the unit 5. The mutual distance between each pair of adjacent partitions 54 corresponds to the mutual distance. between each pair of nearby radiating patches 11. Thus, the hollow metal structure 3, 5 forms box-shaped compartments located in the center of respective, radiating patches 11 and associated feeding elements 21a, 41a and pairs of orthogonal slots 31a, 31b.

The partitions 54 extend along the entire width between the side walls 52 and 53. However, their height is slightly smaller than the distance between the lower wall 51 and the layer 4, so that a free space is formed therebetween. At least some of the partitions should in any case cover only a portion of the cross-sectional area of ​​the box-shaped metal structure to accommodate the metal strips of the supply network without making contact.

In the embodiment of Fig. 1, the partitions 54 are formed of separate metal pieces, for example made of aluminum, which are fixed to the lower wall 51 and / or the side walls 52, 53.

In order to achieve the desired function of preventing longitudinal microwave propagation, partitions 54 can be replaced by other forms of discontinuities in the lower wall or side walls 51, 52, 53. It is essential to avoid a constant cross-section along the box-shaped structure which could act as a waveguide. and give rise to resonances, unwanted coupling and energy losses in the form of radiation and heat. The ground plane layer 3 can either be mechanically connected

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509 749 the base unit 5 or capacitively coupled thereto for the particular frequencies used.

In the second embodiment shown in Figure 2, the multilayer structure with radiant patches 11, orthogonal slots 31a, 31b and feed elements 21a, 41a, 21b, 41b is substantially the same as in Figure 1. However, the hollow metal structure is different in that the box-shaped compartments is formed by substantially closed metal frames 60 inserted between the multilayer structure 1-4 and the rear or lower wall 51.

Each frame 60 is located opposite the associated feed elements 21a, 41a, the orthogonal slots 31a, 31b and respective, patch 11. The frames 60 are distributed along the antenna in the longitudinal direction. In the respective frame 60 there are two opposite side wall portions 61, 62, a first transverse wall 63 and a second transverse wall 64. The latter is provided with openings 65 which accommodate the supply network conductors connected to the supply elements 21a. Normally, such openings extend only partially through the wall. IN

2C generally, the openings or recesses may be located in one or more of the walls of respective frame 60.

The frames 60 need not be electrically connected to the rear wall 51 or the ground plane 3. However, it is essential that each wall element of the conductive frame 60 be of such width as to provide a significant capacitive connection to the ground plane 3 through the multi-layer dielectric material. The frames interrupt or reduce microwave propagation outward from the aperture in the region between the rear or lower wall 51 and the multi-layer structure. The frames may be mechanically connected to the multilayer structure 2-4. In addition, the frames 60, in combination with the associated pairs of orthogonal slots, ensure effective isolation between the two polarizations in each antenna element.

A third embodiment is shown in Figure 3. This includes a similar multi-layer structure 1, 2, 3, 4 with radiant patches 11, orthogonal slots 31a, 31b and feed elements 21a, 41a, 21b.

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41b. However, the metal reflector device is different in that the box-shaped compartments are made up of separate, flat box 70s at the back which are located opposite and centered relative to the corresponding patches 11 and associated pairs of orthogonal slots.

Each flat housing unit 70 has a rectangular bottom wall 71 and four side walls 72, 73. One side wall 72 has a recess 72a and another side wall 73 a recess 73a for housing the feed strips connected to the feed elements 21a, 41a, 21b, 41b.

The four side walls 72, 73 are provided with upwardly projecting pins 74, conveniently formed when punching a metal sheet into a metal blank. The flat box unit 70 is made of the blank by bending the portions which form the side walls 72, 73.

The layers 1, 2, 3, 4 are provided with boreholes 14 in rectangular patterns corresponding to the upwardly projecting pins 74. Upon mounting, the upwardly extending pins 74 are inserted into the holes 14, whereupon the pins are soldered to direct electrical contact with the ground plane 3. In this way, the ground plane 3 to be securely connected to the flat charging units 70, mechanically as well as electrically.

The flat bearing units 70 may be substantially rectangular, square, polygonal or circular, seen in plan view. It has been found that the embodiment of Fig. 3 is very convenient to manufacture by punching, bending and soldering operations. Also, the functional characteristics are excellent with very effective insulation between the different patches and between the double polarized carriers.

In all embodiments shown in the drawings, the orthogonal slots shall be placed in such a symmetrical arrangement that the electromagnetic field components in each channel do not interfere with each other.

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