GB2397697A

GB2397697A - Folded flexible antenna array

Info

Publication number: GB2397697A
Application number: GB0301389A
Authority: GB
Inventors: Peter Godsland
Original assignee: Siemens AG; Roke Manor Research Ltd
Current assignee: Siemens AG
Priority date: 2003-01-22
Filing date: 2003-01-22
Publication date: 2004-07-28
Also published as: WO2004066444A1; GB0301389D0

Abstract

A tile for an antenna array comprising a flexible substrate 6 having antenna elements located thereon. One or more a rigid boards 7, such as a PCB, may be attached locally/ regionally to give localised stiffness to the substrate. One end of the film includes the antenna elements and the other contains said flexible film 6 is folded over so as the other end provides substantial reflectance. The flexible substrate includes circuitry 5 to perform antenna tile associated functions e.g. quad hybrids.

Description

ELECTRONIC CIRCUIT ARRANGEMENT

s 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.

lo 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 is 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 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.

The problem with such designs is such current designs are not robust. The pins and associated solder joints are susceptible to failure due to vibration, high G force. Further, the performance is poor due to the difficulty 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 s processing board. Furthermore resistors used for e.g. Wilkinson couplers of the existing tile need to be mounted on the surface of the processing board. This requires 100 ohm matched vies 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 lo capacitance and hence poor impedance matching resulting in a reduction of performance. The construction of the tile is expensive and time consuming.

It is an object of the invention to overcome the above problems The invention will now be described by way of example and with reference to the following figures of which: Figure 1 shows a conventional prior art tile 1 arrangement Figure 2 shows an example according to the invention.

Figure 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 the antenna elements 3. The antenna elements used for the tile illustrated in figure 1 are dipole antennas. Quad hybrids which are used to isolate transmit and receive ports. The lower board 4 includes the electronics 5 associated with the receiver such as for isolation, amplifying, combining, splitting and phase shift functions These are necessarily - 2 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 s reflect signals propagated downward and thus to increase the emitted signal.

Figure 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 lo both the associated electronic as well as the tile elements printed on it.

Such a flexible film may be fabricated from DuPont 'M Pyralux( AP9161 all polyimide laminate Thus the fabrication of a layer of the tile processing board and antenna board in one process Is Figure 3 shows how the flexible film of figure 2 is folded over to provide a low radar cross section tile. Part of the flexible film is included as the top layer of the printed circuit board layer stack 7. The printed circuit board stack acts to improve the rigidity as well as providing space for electronic components. The antenna section 8 is folded over to be above to 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 enhance the rigidity s 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. - 3

The outputs from the antenna elements are in this case 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 s 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 lo 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 vies to these components improves the is impedance matching and hence the Voltage Standing Wave Ratio (VSWR) and hence the overall performance of the tile. Because of the easy fabrication process, with no intricate assembly the time to assemble tiles according to the invention is lower as is the cost of production. Because no soldering is used and no joints are made between the processing board to and the antenna board the system reliability will be improved and the tile is much less likely to fail due to stressful environmental conditions.

Because the combiner can be printed on the top of the processing printed circuit board, the resistors that maybe necessary to form the individual couplers can be simply attached to the couplers requiring no through Is printed circuit board vies.

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 1/8'h of a wavelength at - 4 the frequency used. This enables the antennas to be placed to of a wavelength above the reflector / processing board.

The antennas used for the tile illustrated in figure 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 to 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 single piece of flexible film or laminate for the printing of antennas, quad hybrids and microstrip transmission Is lines, footprints for MMICs, amplifiers, phase shifters and couplers. The 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 to 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. Because there are no connections that might otherwise be difficult to impedance match, the performance of the tiles is improved with a lower noise figure and higher as gains than has been achieved with other approaches. s

Claims

Claims 1. A tile for an antenna array comprising a substrate having

antenna s elements located thereon characterized in that substrate is flexible.
2. A tile as claimed in claim 1 wherein including one or more a rigid boards attached locally/ regionally to give localised stiffness to the laminate.
3. A tile as claimed in claims 1 or 2 wherein one end of the film includes the antenna elements and the other contains said flexible film is folded over so as the other end provides substantial reflectance
4. A tile as claimed in claim 3 wherein said fold is approximately 180 degrees.
5. A tile as claimed in claims 1,2,3 or 4 wherein said rigid board are printed circuit boards (PCB's) or a PCB layer stack.
6. A tile as claimed in claim 5 wherein said PCB or PCB stack includes some circuitry to perform functions associated with said antenna tiles.
7. A tile as claimed in any preceding claim wherein said flexible substrate includes some circuitry to perform antenna tile associated functions - 6
8. A tile as claimed 7 wherein said circuitry includes quad hybrids.
9. A tile as claimed in claim 8 wherein said quad hybrids are located on the antenna element portion or the bend of said film. s - 7