WO2007063484A2

WO2007063484A2 - An antenna coupler

Info

Publication number: WO2007063484A2
Application number: PCT/IB2006/054472
Authority: WO
Inventors: Paul A. Gough; Peter J. Massey; Matty J. Bickerton
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-11-30
Filing date: 2006-11-28
Publication date: 2007-06-07
Also published as: WO2007063484A3

Abstract

A receptacle (60) for retaining a portable electronic device (68) and coupling electromagnetic signals between the receptacle and the device. The device comprises a ground plane (12) and an antenna element (16). The receptacle comprises a first sidewall (20) comprising a first conductive sheet (24) and a second sidewall (22) comprising a second conductive sheet (26). The receptacle further comprises an opening (210) for disposing a portable electronic device between the first and second sidewalls, and when the device is disposed into the receptacle, the device is retained by the first and second sidewalls, and the first and second conductive sheets couple to the device's ground plane and antenna element.

Description

DESCRIPTION

AN ANTENNA COUPLER

This invention relates to a receptacle for retaining a portable electronic device, and more specifically to a means of coupling electromagnetic signals between the receptacle and the device.

Portable electronic devices are often placed in poor electromagnetic signal reception areas where device antennas cannot receive a sufficient signal strength for the received signal to be interpreted correctly. For example, mobile phones frequently lose adequate signal strength to receive incoming calls, and GPS positioning devices frequently fail to receive signals from enough satellites to give a reliable position fix.

One solution is to increase the size of the antenna, however portable electronic devices are often very space restricted, and no additional space can be designated for a larger antenna. Furthermore, for ease of handling and aesthetic reasons, device antennas are increasingly being placed on the inside of devices rather than protruding externally. This even further restricts the space available for the antenna.

The poor signal reception problem has been addressed by the use of docking stations for portable electronic devices, whereby the portable electronic device is set in the docking station and the docking station provides a larger remote antenna in a better signal reception area to increase the signal strength received by the device. The docking station may even actively boost the received signal strength before the signal is passed to the portable device.

One method of connecting the remote antenna is to plug it directly into the device, however this requires the device to have a socket for a particular remote antenna's plug. Another method is to connect the remote antenna directly to the antenna of the device. However neither these methods are very convenient to use in practice. An improved method that requires no plug & socket connection is to use a docking station comprising a coupler that is connected to a remote antenna. The portable device's antenna is placed in close proximity to the coupler, thereby coupling electromagnetic signals between the device's antenna and the coupler that is connected to the remote antenna.

Various means of coupling electromagnetic signals between a portable electronic device and a docking station are known in the art. For example, United States Patent US6112106 discloses a docking system for connecting a portable communication device having an external radiative antenna to a further signal transmission line. At least a portion of the external radiative antenna is inserted into a shielded housing of the docking system. The shielded housing has a coupling probe mounted within it for radiatively coupling to the external antenna. However, the docking station and shielded housing can only accept mobile devices having a particular size and antenna location so that the antenna correctly enters the shielded housing when the device is placed in the docking station. Furthermore the docking station cannot couple effectively to devices that have an internal antenna.

European Patent Application EP0999607 discloses an antenna coupler for coupling a radio telecommunication device having an integral planar antenna to an external device. The integral planar antenna comprises a first planar conductive antenna element with a larger ground plane behind the first element and the antenna coupler comprises a second planar conductive antenna element with a larger conductive ground plane behind the second element. The telecommunication device is attached to the antenna coupler such that the first and second planar conductive antenna elements face one another, and at least a portion of the larger ground planes also face one another. Then, electromagnetic signals couple between the telecommunication device and the antenna coupler by means of the first and second antenna elements and the larger ground planes. The telecommunication device must be orientated with the antenna coupler such that the first and second antenna elements face towards one another, without there being a larger ground plane between them. Otherwise the majority of the electromagnetic energy would not be coupled between the antenna elements. There is a need for antenna couplers that are simpler to use, easier to construct, and that give more efficient coupling.

It is therefore an object of the invention to provide an antenna coupler that improves upon the known art.

According to a first aspect of the invention, there is provided a receptacle for retaining a portable electronic device and coupling electromagnetic signals between the receptacle and the device, the device comprising a ground plane and an antenna element, the receptacle comprising:

- a first sidewall comprising a first conductive sheet;

- a second sidewall comprising a second conductive sheet;

- an opening for disposing the portable electronic device between the first and second sidewalls, and wherein upon disposal: o the device is retained by the first and second sidewalls; and o the first and second conductive sheets couple to the device's antenna element and ground plane.

Owing to the first aspect of the invention, there is provided a receptacle comprising two sidewalls, the sidewalls operable to both retain a portable electronic device and to couple electromagnetic signals to and from the device.

Advantageously, due to the sidewalls both retaining the device and coupling to the device, a receptacle may be manufactured simply by joining together the edges of two sidewalls that face toward one another, with a portion of the edges only temporarily fixed, or left open, for disposing a portable electronic device.

Furthermore, the receptacle may accept a large variety of differently shaped electronic devices, with the receptacle sidewalls adapting to retain the device by means of elastication or shape memory alloys, hence keeping the conductive sheets in close proximity to the device's antenna element and ground plane for efficient coupling.

Advantageously, the receptacle's sidewalls may collapse towards one another once the portable electronic device is removed from the receptacle, reducing the space occupied by the receptacle when not in use.

Furthermore, the receptacle may further comprise a third conductive sheet, for shielding electromagnetic signals from the environment external to the receptacle.

Additionally, the receptacle may be incorporated into a garment as a pocket constructed from woven fibres. The two conductive sheets may be formed, for example, by plating areas of the woven fibres with metal, or by interweaving conductive fibres along with the woven fibres. This would be a very simple way to incorporate an antenna coupler into a garment, and would be very comfortable and convenient for a wearer of the garment to use.

Furthermore, the first and second conductive sheets may be connected to a remote antenna via a transmission line to increase the signal strength received by the electronic device. The US Granted Patent US6680707 of the same applicant and entitled "Garment Antenna" discloses suitable techniques for creating a garment with an incorporated remote antenna, whereby the remote antenna may be connected to a portable electronic device for telecommunications purposes.

The larger size and / or more favourable positioning of the remote antenna over the device antenna can more than compensate for the signal strength losses incurred in the antenna coupler. The size and positioning restrictions on the remote antenna are often much less severe than the size and positioning restrictions on the device antenna.

The receptacle is also expected to find applications in receiving navigational positional signals like GPS, wherein a remote antenna positioned on the shoulder of a user and having a direct line of sight to transmitting satellites receives a much stronger signal than an antenna positioned in the user's pocket. Embodiments of the invention provide an easily manufactured and efficient antenna coupler receptacle, which can accept and retain a wide variety of differently shaped devices, and automatically bring the receptacle's coupling sheets within close proximity to the device for efficient coupling.

Further features of the invention will become apparent from the embodiments now described, by way of example only, and with reference to the accompanying drawings, in which:-

Figure 1 shows diagrams of a typical portable electronic device having a ground plane and an antenna element;

Figures 2a, 2b, and 2c show diagrams of a receptacle having two sidewalls each comprising a conductive sheet;

Figure 3 shows a diagram of the device of Figure 1 disposed in the receptacle of Figure 2;

Figures 4a, 4b, and 4c show schematic diagrams of a receptacle having a third conductive sheet and compensatory reactance;

Figure 5 shows a diagram of a receptacle connected to a remote antenna via a transmission line; and

Figure 6 shows a diagram of a garment incorporating a receptacle, transmission line and remote antenna.

Figure 1 shows plan and cross-sectional diagrams of an exemplary portable electronic device suitable for coupling to the receptacle of the invention. The device comprises an outer housing 10, a ground plane 12, an insulating material 14, and an antenna element 16. Other device circuitry is not shown for clarity. The top of the outer housing 10 in the plan diagram is not shown for clarity. The antenna shown in Figure 1 is a patch antenna, however other antenna arrangements having a ground plane and antenna element may also be used, like for example Planar Inverted F (PIFA) antennas, as will be apparent to those skilled in the art. The device is for example a mobile telecommunications device or a GPS navigational device. Figures 2a and 2b show front and back diagrams of an exemplary receptacle according to the invention. Figure 2c shows a cross-sectional diagram along A-A as indicated on figure 2a. The receptacle comprises a first sidewall 20 and a second sidewall 22. The first sidewall 20 comprises a first conductive sheet 24 and the second sidewall 22 comprises a second conductive sheet 26. There is an opening 210 between the sidewalls for disposal of a portable electronic device. The first and second sidewalls are formed from for example plastics or textiles, and the conductive sheets are formed from any conductive material, for example copper or woven conductive thread.

Figures 2a - 2c show the first and second sidewalls interspaced by further sidewalls 28, however in other embodiments the first and second sidewalls may be directly joined together along their edges by for example stitching them together. In an embodiment, the sidewall edges forming the opening 210 may be temporarily fixed together to close the receptacle, for example by means of a zip, a button, or any other suitable fastener. In another embodiment, the sidewall edges forming the receptacle opening 210 are left unfixed.

Figure 3 shows a cross-sectional view of the electronic device of Figure 1 disposed in the receptacle of Figures 2a - 2c. The first and second conductive sheets 24 and 26 couple to the device's antenna element 16 and the device's ground plane 12 respectively, enabling the transfer of signals between the device and the receptacle. The housing 10 of the device is retained within the receptacle by the sidewalls 20 and 22. Figure 3 shows the whole of the device enclosed between the sidewalls 20 and 22, although, in other embodiments, a portion of the device may remain protruding from the receptacle.

In an example embodiment, the sidewalls are elasticised to more securely retain the electronic device and to bring the sidewalls closer to the electronic device. This consequently brings the conductive sheets 24 and 26 closer to the ground plane 12 and antenna element 16, increasing the coupling efficiency. In a further embodiment, the receptacle comprises shape memory alloy wire that is embedded into the receptacle sidewalls. When the shape memory alloy wire is heated it contracts, causing the pocket to deform around the electronic device, and hence retaining the device and bringing the conductive sheets 24 and 26 closer to the ground plane 12 and antenna element 16. The shape memory alloy wire (For example Nitinol) is heated by passing an electric current through it, and so the contraction of the wire can be controlled. Such a shape memory alloy controlled pocket is disclosed in the commonly assigned US granted patent US 6834797.

In a preferred embodiment, the conductive sheet 26 faces towards the whole of the area of the ground plane 12, as shown in Figure 3. This shields the electromagnetic energy from the environment external to the receptacle and minimises losses. Since the antenna element 16 typically has a smaller area than the ground plane 12, the receptacle in a preferred embodiment has differently sized first and second conductive sheets to match the differently sized ground plane and antenna element, as shown in Figure 3.

For optimum coupling efficiency, the device should be disposed into the receptacle such that the antenna element 16 faces the smaller conductive sheet 24 as shown in Figure 3. If the device is placed in the receptacle such that the antenna element 16 faces the larger coupling sheet 26, then coupling will still occur, but at a lower efficiency.

Since a large variety of electronic devices have their antenna element 16 at one end of the device, receptacles having a conductive sheet 24 at the bottom of the receptacle, as shown in Figure 3, are able to efficiently couple to a large variety of electronic devices.

In order to attain optimal coupling efficiency for a particular device, the conductive sheet 24 could be placed at a position within sidewall 20 according to the position of the antenna element 16 on the device. A receptacle could be marketed as being particularly well suited to a selection of devices that have their antenna element 16 in a favourable position relative to the position of the conductive sheet 24. For example, in the case where the device is a GPS navigational device having a circularly polarised patch antenna, the inventors have found that optimal coupling efficiency is achieved when the conductive sheet 24 faces at least one of the antenna element's edges and between a quarter and a third of the antenna element's area, as shown in Figure 3. As the area over which the coupling sheets face one another is altered from this preferred range, the coupling efficiency decreases.

Figures 4a and 4b show front and back views of a receptacle of a further embodiment, and Figure 4c shows a cross-sectional view through A-A as indicated on Figure 4a. The first sidewall 20 of the receptacle further comprises a third conductive sheet 40, the third conductive sheet facing the first conductive sheet 24 and disposed between the first conductive sheet 24 and the exterior of the receptacle. The first and third conductive sheets are electrically insulated from one another by for example spacing them apart from one another or separating them by an insulting layer like a non-conducting fabric or plastic. The third conductive sheet is electrically connected to the second conductive sheet 26 by means of a wired connection 42, however in a further embodiment the third and second conductive sheets extend over a portion of the sidewalls 28 and are joined directly together.

The third conductive sheet 40 shields the electromagnetic radiation that is radiated from the first conductive sheet 24, reducing the electromagnetic energy that is absorbed outside of the receptacle, as will be apparent to those skilled in the art. The third sheet is particularly advantageous when the receptacle is placed close to an electromagnetically lossy material like the user's body.

The first and third conductive sheets inherently form a parallel-plate capacitor at low frequencies, or a waveguide with fringing effects at higher frequencies, in both cases introducing a reactance that reduces the coupling efficiency. To address this, a reactance 44 may be connected between the first and third conductive sheets, to compensate for the reactance inherently formed by the first and third conductive sheets, and to minimise the reduction in coupling efficiency. For full compensation, the reactance 44 is sized to have a reactance opposite to that inherently formed by the first and third conductive sheets. For example, at low frequencies having a wavelength of more than ten times the length of overlap of the first and third conductive sheets, the first and third conductive sheets form a capacitive reactance that may be compensated for by connecting an inductive reactance between the sheets. As will be apparent to those skilled in the art, the capacitance may be approximated as C = εA/d and the required inductance for full compensation is calculated as L = 1/(ω_c ²C), wherein: ε = permittivity between first and third conductive sheets;

A = area over which the first and third conductive sheets face one another; d = average distance between first and third conductive sheets; ω_c = centre frequency of operating frequency range (ω_mιn up to ω_maχ), wherein ω_c = V(ω_mιn ^*ω_maχ).

At higher frequencies having a wavelength less than ten times the length of overlap of the conducting sheets, the first and third conductive sheets begin to act less like a parallel plate capacitor and more like a waveguide, and the reactance is better calculated using an electromagnetic simulation software package like HFSS™, as will be apparent to those skilled in the art.

Figure 5 shows a diagram of a receptacle connected to a remote antenna via a transmission line. The receptacle comprises first and second sidewalls 20 and 22 having first and second conductive sheets 24 and 26 respectively. The transmission line has an inner conductor 58 enclosed by an outer shielding conductor 56, and the remote antenna has a ground plane 54 and an antenna patch 50 that are insulated from one another by the insulator 52. The first conductive sheet 24 is connected to the remote antenna patch 50 via the inner transmission line conductor 58. The second conductive sheet 26 is connected to the remote antenna ground plane 54 via the outer transmission line conductor 56.

The portable electronic device is preferably disposed into the receptacle as shown in Figure 3, wherein the device's antenna element 16 couples to the first conductive sheet 24 and the device's ground plane 12 couples to the second conductive sheet 26. Then, the coupled signal from the device's antenna element 16 is carried to the remote antenna's patch 50 via the inner conductor 58, and the coupled ground from the device's ground plane 12 is carried to the remote antenna's ground plane 54 via the outer shielding conductor 56. If the device is disposed into the receptacle such that the device's ground plane 12 couples to the first conductive sheet 24 and the device's antenna element 16 couples to the second conductive sheet 26, then the polarities of the conductors 56 and 58 and of the remote antenna elements 50 and 54 are reversed, and the efficiency of the transmission line and remote antenna is reduced.

Figure 6 shows a garment incorporating a receptacle 60, a transmission line 62, and a remote antenna 64. A portable electronic device 68 is disposed within receptacle 60. In an embodiment, the receptacle sidewalls are formed by textiles and incorporate woven conductive threads forming the conductive sheets. The transmission line 62 is a thin co-axial cable that runs on top of or inside of the fabric of garment 66. The remote antenna 64 is formed from two layers of conductive fabric and a layer of insulating fabric, the layer of insulating fabric disposed between the two layers of conductive fabric.

In other embodiments, the receptacle sidewalls are formed from other materials like plastics and the conductive sheets are formed from other materials like thin metallic sheets. In further embodiments, the transmission line is formed by first and second conductors woven into the garment. In still further embodiments, the remote antenna is formed from metallic sheets or is of a different type to the patch antenna previously described.

Claims

1. A receptacle (60) for retaining a portable electronic device (68) and coupling electromagnetic signals between the receptacle and the device, the device comprising a ground plane (12) and an antenna element (16), the receptacle comprising:

- a first sidewall (20) comprising a first conductive sheet (24);

- a second sidewall (22) comprising a second conductive sheet (26); and

- an opening (210) for disposing the portable electronic device (68) between the first and second sidewalls, and wherein upon disposal: o the device is retained by the first and second sidewalls; and o the first and second conductive sheets couple to the device's ground plane and antenna element.

2. The receptacle of claim 1 , wherein the first and second sidewalls of the receptacle are arranged to face one another, and wherein:

- a portion of the first and second sidewall edges are fixed together; and

- the remainder of the first and second sidewall edges, which form the opening for disposing the device, are temporarily fixed together or unfixed.

3. The receptacle of claims 1 or 2, wherein the first conductive sheet (24) is of smaller area than the second conducting sheet (26).

4. The receptacle of any preceding claim, wherein the receptacle is elasticised to retain the device between the first and second sidewalls.

5. The receptacle of any of claims 1 to 3, wherein the receptacle comprises a shape memory alloy wire operable to:

- contract under ohmic heating; and

- deform the receptacle, thereby retaining the device between the first and second sidewalls.

6. The receptacle of any preceding claim, wherein the first and second sidewalls are able to collapse together upon removal of a portable electronic device from the receptacle.

7. The receptacle of any preceding claim, wherein the first sidewall further comprises a third conductive sheet (40), the third conductive sheet:

- faces the first conductive sheet (24);

- is disposed between the first conductive sheet and the exterior of the receptacle;

- is separated from the first conductive sheet by an electrically insulating material; and

- is electrically connected to the second conducting sheet (26).

8. The receptacle of claim 7, wherein a reactance (44) is connected between the first and third conductive sheets, the reactance being sized to compensate for the reactance inherently formed by the first and third conductive sheets.

9. The receptacle of any preceding claim, wherein the first and second sidewalls are formed from textiles.

10. The receptacle of any preceding claim, wherein the conductive sheets comprise textiles plated with metal.

11. The receptacle of any preceding claim, wherein the conductive sheets comprise woven conductive fibres.

12. The receptacle of any preceding claim, and wherein upon disposal, the whole device is enclosed between the first and second sidewalls.

13. The receptacle of any preceding claim combined with a transmission line (62) and a remote antenna (64), wherein the first and second conductive sheets (24, 26) of the receptacle are respectively connected to first and second conductors (58, 56) of the transmission line, and wherein the transmission line is further connected to the remote antenna.

14. The combination of claim 13, wherein the remote antenna is able to receive navigational positioning signals.

15. A garment (66) comprising the combination of claims 13 or 14.

16. The garment of claim 15, wherein one or both of the transmission line and remote antenna comprise woven conductive fibres.