WO2004066444A1

WO2004066444A1 - A tile for an antenna array

Info

Publication number: WO2004066444A1
Application number: PCT/GB2004/000074
Authority: WO
Inventors: Peter Godsland
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-01-22
Filing date: 2004-01-12
Publication date: 2004-08-05
Also published as: GB2397697A; GB0301389D0

Abstract

A tile for an antenna array comprises a flexible substrate (6) having antenna elements (3) located thereon. A first end (8) of the substrate (6) including the antenna elements is folded over, such that a second end (9) of the substrate provides substantial reflectance.

Description

A TILE FOR AN ANTENNA ARRAY This invention relates to an apparatus for supporting electronic components wherein two flat areas have to be provided parallel to each other and separated by a short distance. It is particularly applicable to tiles of multiple phased array antennas. Phased tile arrays are antenna arrays which have application in e.g. satellite communications. The tiles are typically triangular or rectangular and are mosaiced up to form a dodecahedron or an array which conforms to the body of an e.g. an aircraft. These have advantages over dish-based arrays; the latter are more prone to being jammed. The tiles can be selectively switched on individually to provide beam patterns in a particular direction.

Such tiles comprise two boards arranged parallel to each other separated by a short distance. One of the boards, the top board, has a plurality of the flat antenna elements. Located parallel to the top board is a bottom board, spaced therefrom. These bottom boards comprise the associated electronics required for effective transmission and reception from the antenna element; and may include a quad hybrid, a combiner, splitter, amplification and phase shift functions. Existing designs have used pins as electrical connections between the boards.

A problem with such designs is that current designs are not robust. The pins and associated solder joints are susceptible to failure due to vibration, or high G force. Further, the performance is poor due to the difficulty of impedance matching the pins from the processing board to the antenna board. Construction is also difficult, requiring two printed circuit boards and soldered pins necessitating skilled assembly. Additionally, component density is poor with e.g. quad hybrids using valuable space on the processing board. Furthermore resistors used e.g. for Wilkinson couplers of the existing tile need io be mounted on the surface of the processing board. This requires 100 ohrn matched vias from the couplers (buried in the printed circuit board layer stack") to the surface of the printed circuit board. These are difficult to fabricate without stray inductance and capacitance and hence poor impedance matching results in a reduction of perfoπnance. The construction of the tile is expensive and time

In accordance with the present invention, a tile for an antenna array comprising a substrate having antenna elements located thereon is characterised in that the substrate is flexible. Preferably, a first end of the substrate including the antenna elements is folded over, such that a second end of the substrate provides substantial reflectance.

The second end reflects signals propagated downwards, thereby increasing the emitted signal, whilst the fold provides a robust connection between the antem a and processing sections.

Preferably, the substrate is folded through approximately 180 degrees.

This results in the antenna and processing sections being substantially parallel, improving the antenna effectiveness.

Preferably, the tile further includes one or more a rigid boards attached locally or regionally to give localised stiffness to the laminate.

Preferably, the or each rigid board is a printed circuit board (PCB) or a PCB layer stack.

Typically, the PCB or PCB stack includes some circuitry to perform functions associated with said antenna tiles. Preferably, the flexible substrate includes some circuitiy to perform antenna tile associated functions

Typically, the circuitry includes quad hybrids.

Preferably, the quad hybrids are located on the first end of the substrate, or the bend of the substrate. Preferably, the substrate is a flexible film.

An example of a tile for an antenna array in accordance with the present invention will now be described by way of example and λvith reference to the following figures in which:

Figure 1 shows a conventional prior art tile 1 arrangement; Figure 2 shows an example according to the invention; and,

Figure 3 shows the example of Fig.2, folded o^~"er.

Fig. 1 shows a conventional prior art tile 1 used in plurality to mosaic an antenna array. It comprises two rigid boards, an upper board 2 which carries antenna elements 3 and a lower board 4. The antenna elements used for the tile illustrated in Fig. 1 are dipole antennas, quad hybrids which are used to isolate transmit and receive ports. The lower board 4 includes electronics 5 associated with the receiver such as for isolation, amplifying, combining, splitting and phase shift functions. These are necessarily placed on the lower board because they would take up too much room on the upper board, which is primarily for the antenna elements themselves. Additionally the antennas are more effective if the lower board is located parallel and under the antenna board. In this way the lower board acts to reflect signals propagated downward and thus to increase the emitted signal.

Fig. 2 shows a simple embodiment of the invention, used as the basic feature of a novel antenna tile. A flexible film 6 is provided which has both the associated electronics 5 as well as the tile elements 3 printed on it. Such a flexible film may be fabricated from DuPont™ Pyralux® AP9161 or polyimide laminate. Thus the fabrication of a layer of the tile processing board and antenna board is done in one process.

Fig. 3 shows how the flexible film of Fig. 2 is folded over to provide a low radar cross section tile. Part of the flexible film 6is included as the top layer of a printed circuit board layer stack 7. The printed circuit board stack acts to improve the rigidity as well as providing space for electronic components. An antenna section 8 is folded over to be above the processing board 9 (the plated underside of which also acts as a reflector), without the use of any soldered pins. Not shown in this example, the antenna section may preferably also be attached to a board to enhance the rigidity. Furthermore, in a preferred embodiment, the upper and lower portions may be separated using rigid spacers to enliance the rigidity either with or without the rigid boards. In all cases there is a connection from the antenna elements to the lower portion via the bend which is robust.

The outputs from the antenna elements are, in this example, matched to a 50 ohm microstrip transmission line, in this case using quarter wavelength long microstriplines of the geometric mean impedance between the antenna impedance and 50 ohms. The microstriplines from all of the antenna elements are then transferred to one edge of the antenna section of the flexible film such that they can be transferred to the processing section of the board using the flexible loop section of the film. The quad-hybids can be printed onto the antenna section of the film or on the bend in the material, increasing the component density. The area that previously had to be used for the quad hybrids can therefore be used for other components such as low profile Monolithic Microwave Integrated Circuits (MMICs) and combiners. The lack of through board vias to these components improves the impedance matching and hence the Voltage Standing Wave Ratio (NSWR) and hence the overall performance of the tile. The time to assemble tiles according to the invention is lower, as is the cost of production, because of the easy fabrication process, with no intricate assembly. The system reliability will be improved and the tile is much less likely to fail due to stressful environmental conditions, because no soldering is used and no joints are made between the processing board and the antemia board. The resistors that may be necessary to form the individual couplers can be simply attached to the couplers requiring no through printed circuit board vias, because the combiner can be printed on the top of the processing printed circuit board.

Other copper clad laminates with suitable dielectric and physical properties allowing low loss microstrip tracks at the frequencies can be used, and e.g. with a bend radius of approximately l/8th of a wavelength at the frequency used. This enables the antennas to be placed '/. of a wavelength above the reflector / processing board. The antem as used for the tile illustrated in Fig. 2 are patch/slot antennas, although this method could also be used with other printed antenna types such as dipoles or folded dipoles.

To increase the component density of the tile, the quad hybrids, used to isolate the transmit and receive ports and to provide a circularly polarised signal to the antennas, are preferably located on the antenna section of the film and on the bend itself.

The invention involves the use of a single piece of flexible film or laminate for the printing of antennas, quad hybrids and microstrip transmission lines, footprints for IvlMICs, amplifiers, phase shifters and couplers. This means that the signals from the processing board can be transferred to and from the antennas without the use of soldering or unreliable connections. The flexible film will form one of the layers of the layer stack of the processing printed circuit board. The microwave component density of a tile using this method is increased because quad hybrids are able to be printed on the antenna section of the flexible film, or the bend between the antenna section and the processing section. The performance of the tiles is improved with a lower noise figure and higher gains than has been achieved with other approaches, because there are no connections that might otherwise be difficult to impedance match.

Claims

1. A tile for an antemia array comprising a substrate having antenna elements located thereon characterised in that the substrate is flexible.

2. A tile according to claim 1 , wherein a first end of the substrate including the antenna elements is folded over, such that a second end of the substrate provides substantial reflectance.

3. A tile according to claim 2, wherein the substrate is folded through approximately 180 degrees.

4. A tile according to any preceding claim, including one or more a rigid boards attached locally or regionally to give localised stiffness to the laminate.

5. A tile according to claim 4, wherein the or each rigid board is a printed circuit board (PCB) or a PCB layer stack.

6. A tile according to claim 5, wherein the PCB or PCB stack includes some circuitry to perform functions associated with said antemia tiles.

7. A tile according to any preceding claim, wherein the flexible substrate includes some circuitry to perform antenna tile associated functions

8. A tile according to claim 7, wherein said circuitry includes quad hybrids.

9. A tile according to claim 8, wherein- the quad hybrids are located on the first end of the substrate, or the bend of the substrate.

10. A tile according to any preceding claim, wherein the substrate is a flexible film.