GB2418542A

GB2418542A - Adjustable phase shifter

Info

Publication number: GB2418542A
Application number: GB0421163A
Authority: GB
Inventors: Philip Johnston
Original assignee: Trackwise Designs Ltd
Current assignee: Trackwise Designs Ltd
Priority date: 2004-09-23
Filing date: 2004-09-23
Publication date: 2006-03-29
Anticipated expiration: 2024-09-23
Also published as: GB2418542B; GB0421163D0

Abstract

An adjustable phase shifter comprises two printed circuit boards 11 and 21 which are mutually slidable. A stripe of material 13 is provided on the pcb 11 to act as a glide surface. The material 13 comprises a lubricant such as Teflon ¹ and a photo-resist (or solder resist).

Description

24 1 8542

IMPROVEMENTS RELATING TO ADUSTABLE ANTENNAS

This invention relates to improvements in components for antennas, and in particular to an improved electrical component for a phase shifter. It is especially suited to phase shifters of antennas for use in a mobile phone network.

The increasing prevalence of mobiles phones has seen a corresponding increase in the need for antennas. These are usually located on the top of masts in locations, which provide a reasonably clear sight line to the areas in which mobile phones are to be used. To minimize the amount of power consumed by an antenna, the radiation pattern or beam pattern of the antenna can be chosen such that more power is sent to the area in which a greater number of phone users are located (such as a nearby town) whilst less power is sent to areas with fewer users (such as adjacent countryside).

In the past the shaping of beam patterns was performed when the antenna was installed by a skilled fitter who would physically adjust the antenna.

Typically this meant tilting a fixed pattern antenna relative to its support mast. This had severe limitations and did not allow the pattern to be altered during service. Then came variable tilt antennas in which the angle of tilt could be adjusted within the antenna at the time of manufacture. This had the advantage that a standard fitting could be made to the antenna with the pattern being tailored before fitting taking into account the desired pattern and mast location. Some tweaking could also be made by the installer after physically mounting the antenna.

At present mobile telephone service providers are demanding antennas whose beam pattern can be adjusted in use, and often require such adjustment to be made remotely. This allows, for example, the antenna to cope with different patterns of use throughout a day as phone users move between the city during the day and the suburbs at night.

The typical solution is to use a phase shifter in which an antenna is constructed from two antenna elements which can be moved relative to one another using a suitable actuator. The pattern of the beam is determined by inductive coupling between the two elements which in turn is dependent upon their relative position and shape. The applicant has appreciated that to implement such an antenna successfully there is a need for a mechanism for permitting the two elements to move relative to one another which must be simple and reliable and preferably of low cost.

The present invention addresses this need.

According to a first aspect the invention provides an adjustable phase shifter structure comprising first and second portions, a first portion carrying a first conductive element which is inductively coupled to a different electrical track on a second portion to define a phase shifter, in which: the first portion comprises a support surface which has provided thereon the first conductive element, the second portion comprises a second support surface which has provided thereon the second conductive element, the first portion abutting the second portion and arranged for relative movement therebetween; and in which the first portion also carries a layer of solder resist material combined with a lubricant, the combined layer defining a surface upon which the second portion may slide relative to the first portion.

The first and second support surface may comprise surfaces of respective printed circuit boards (PCBS). The first and second conductive elements may comprise electrically conductive tracks which may be printed on the boards using any standard pcb processing technique. They may be metallic tracks.

The combined layer may comprise a layer of solder-resist material deposited, typically by a standard PCB printing process, onto the support surface. A layer of lubricant material may be coated onto the layer of solder-resist.

The lubricant may comprise a powdered lubricant which may be put onto the solder-resist during the print process whilst the photo-resist is still wet. In this way, some of the powder will impregnate the solder-resist. A suitable solder-resist is Tamura Kaken USR2A which can be applied as a layer approximately 0.015mm thick. A suitable lubricant powder is pure PTFE. Other suitable powders are Asahi Glass fluoropolymers grade FL1690.

This arrangement has been found to be both hardwearing and simple to construct. It also permits the two portions to be fabricated using standard printed circuit board construction techniques.

It is preferred that the combined layer is printed on the first support in such a way that it extend at least partly over the electrical track on that support. This ensures that for any given thickness of electrical track the combined layer will always protrude further from the support to define the low friction surface.

This also has the advantage that the combined layer provides the function of electrically insulating the first and second parts from one another. This may, in some arrangements, eliminate the need for a separate insulating layer covering the conductive tracks. In that case the only insualting layer will be the combined layer.

The first and second portions may have an elongate, preferably rectangular shape.

Whilst a combined solder-resist/lubricant layer has been described for the first portion only, the skilled man will understand that both the first and second portions may carry such a layer or a plurality of layers.

According to a second aspect the invention provides a method of constructing a phase shifer, the method including the steps of: taking a first portion which carries a printed electrical track on at least one face, applying to the at least one face an area of solder resist, prior to curing the resist applying a lubricating powder onto the surface of the resist; and curing the combined layer of solder resist and powder such that at least some of the powder adheres to solder resist.

This provides a region on the circuit upon which another phase shifter portion can slide when in use to alter the pattern or direction of the antenna.

The solder resist may be applied across the whole of the face of the first antenna portion. It is preferred, however, if it is applied in a stripe which extends along the surface in a direction which is aligned with direction of relative movement of the first part relative to a cooperating second part of the antenna.

The solder resist is preferably applied to the first antenna portion using a standard PCB processing technique such as screen-printing using an appropriate mask.

There will now be described, by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which: Figure 1 is a plan view of a first part of a steerable antenna according to the present invention; Figure 2 is a plan view similar to Figure 1 of a second part of the antenna which co-operates with the first; and Figure 3 is a cross-sectional view of the first and second parts in their positions of use.

An antenna, suitable for use in a mobile telephony network, includes a phase shifter which has first and second relatively movable antenna portions 10,20. These elements are shown in Figures 1 and 2 of the accompanying drawings respectively.

A first portion defining one phase shifter portion comprises a planar, generally rectangular, printed circuit board 11. The board comprises a support or substrate. In this example the board 11 is (example of board).

On one surface of the substrate is a pattern of electrically conductive tracks 12 which define multiple antenna elements (four are shown). Also shown in the drawings is a stripe of material 13 which defines a glide surface upon which the second element 20 can slide. This stripe 13 extends from one end of the support to the other and comprises a layer of photo-resist material which is impregnated on its surface with a lubricating powder. In the example the powder is Teflon.

The second portion 20 is similar to the first. It also comprises a planar support substrate 21 upon which a pattern of electrically conductive tracks is provided defining four antenna elements 22. Unlike the first element this one does not carry the glide surface, the conductive tracks being arranged to contact the first element. In alternative arrangements there could be a glide surface on both elements.

Figure 3 shows the location of the two portions 10,20 when the phase shifter is in use. The portions are butted up to one another, with the raised elements of the second portion contacting the glide surface 13 of the first portion 10.

Although not shown, the first portion is held fixed on a support whilst the second is moved relative to the first by an actuator which engages with locating holes 23 in the second portion.

The first and second portions 10,20 can be constructed using any standard pcb construction technique. The following is preferred; Because the powdered lubricant is applied to the photo-resist whilst the photo resist material is wet it impregnates the surface of the photo-resist.

As the photo resist cures it holds onto some of the lubricant in the surface. The result is a thin layer of material that serves as an insulator and also has a low resistance. The two elements can therefore move relative to one another easily and with little wearing of the surfaces.

Claims

1. An adjustable phase shifter structure comprising first and second portions, a first portion carrying a first conductive element which is inductively coupled to a different electrical track on a second portion to define a phase shifter, in which: the first portion comprises a support surface which has provided thereon the first conductive element, the second portion comprises a second support surface which has provided thereon the second conductive element, the first portion abutting the second portion and arranged for relative movement therebetween; and in which the first portion also carries a layer of solder resist material combined with a lubricant, the combined layer defining a surface upon which the second portion may slide relative to the first portion.

2. An adjustable phase shifter structure according to claim 1 in which the combined layer comprises a layer of solder-resist material deposited onto the support surface.

3. An adjustable phase shifter structure according to claim 1 or claim 2 in which the first and second support surface comprises surfaces of respective printed circuit boards (PCBS) and the first and second conductive elements may comprise electrically conductive tracks printed on the boards.

4. An adjustable phase shifter structure according to claim 3 in which a layer of lubricant material is coated onto the layer of solder-resist.

5. An adjustable phase shifter structure according to claim 4 in which the lubricant comprises a powdered lubricant put onto the solder-resist during the print process whilst the photo-resist is still wet.

6. An adjustable phase shifter structure according to any preceding claim in which the combined layer is printed on the first support in such a way that it extend at least partly over the electrical track on that support.

7. An adjustable phase shifter structure according to any preceding claim in which the first and second portions have an elongate rectangular shape.

8. A method of constructing a phase shifter, the method including the steps of: taking a first portion which carries a printed electrical track on at least one face, applying to the at least one face an area of solder resist, prior to curing the resist applying a lubricating powder onto the surface of the resist; and curing the combined layer of solder resist and powder such that at least some of the powder adheres to solder resist.

9. The method of claim 8 in which the solder resist is applied across the whole of the face of the first antenna portion.

10. The method of claim 8 in which the solder resist is applied in a stripe which extends along the surface in a direction which is aligned with direction of relative movement of the first part relative to a cooperating second part of the antenna.

11. The method of claim 8, 9 or 10 in which the solder resist is applied to the first antenna portion using a standard PCB processing technique.

12. Ad adjustable phase shifter structure substantially as described herein with reference to and as illustrated in the accompanying drawings.