WO2014091208A1

WO2014091208A1 - Filter assembly and method of manufacture thereof

Info

Publication number: WO2014091208A1
Application number: PCT/GB2013/053223
Authority: WO
Inventors: John Tinker; Martin Gostling; Iain RAWSON; Ian Ridley; Adam WILDER
Original assignee: Radio Design Limited
Priority date: 2012-12-12
Filing date: 2013-12-06
Publication date: 2014-06-19
Also published as: GB201321588D0; GB2505138A; GB201222320D0; GB2505138B

Abstract

Filter apparatus is provided including a filter body in which one or more resonating means (10) are formed. A support member (6) is provided for location over at least a part of one face of the said filter body. At least one transmission line (14) is provided for transmitting one or more radio frequency signals therealong in use. At least one transmission line is located on or associated with the support member (6).

Description

Filter Assembly and Method of Manufacture Thereof

The assembly to which this application relates is an assembly for one or more filters and particularly for filters which are each provided for use in apparatus to receive and/or transmit data signals within specified frequency bands. An example of such apparatus is that which is used in transceiving apparatus for wireless communication apparatus such as Base Transceiver Stations (BTS) for mobile or cell phone networks. The application also relates to a method of manufacture of a filter assembly.

Increasingly there is a demand for different mobile network operators to be able to share antenna locations, typically due to cost savings and/or environmental concerns. In order to do this there is provided at each antenna a number of BTS, one for each service provider. Each operator's service is typically carried in a sub band of the overall frequency band which the apparatus is provided to receive and transmit data signals and, as a result of this, there is a need to be able to separate the respective sub bands and direct the same to the appropriate BTS apparatus for the particular operator to allow further processing of the same. This is typically achieved by providing a filter comprising a plurality of resonating means (i.e. means capable of resonating at a required frequency or frequency range), each of which is shaped and formed so as to allow data signals of a particular frequency sub band to pass therethrough. The resonating means are typically formed in a body of conductive material, such as for example a metal body, and recesses and channels are formed in the same to the appropriate form to allow the resonating means, and thus the filter, to operate in the desired manner. An example of a typical resonating means formed within a filter comprises a cavity, recess or channel provided with an inner conductive surface, and a rod, formed for example from ceramic or metal, located in the cavity, recess or channel and arranged so as to resonate at a required frequency or frequency range. In addition to the shaping of the filter body by machining, conventionally there is required to be provided on a face of the body, and typically the face of the body on which the filter openings are formed, transmission lines which connect and/or cascade the resonating means together. The transmission lines are formed in two parts; a first part which is provided in the form of a trough or channel and which is hereinafter referred to as the outer part of the transmission line, and a second part in the form of an electrically conductive material member suspended in and along, but spaced from the side walls, of the outer first part. The second part is hereinafter referred to as the inner part of the transmission line. The inner part is held in such an arrangement within the filter body that it floats and is separated from the conductive material of the filter body.

The transmission lines, comprising the two parts, are required to be of a particular length and electrical impedance with respect to the resonating means with which the transmission lines are provided. A lid is then typically provided to fit over the open side of the filter body in terms of the resonating means, so as to enclose the transmission lines and resonating means within a sealed environment. Tuning screws are provided which depend through the filter lid and into the respective cavities, channels or recesses of the resonating means to allow the same to be tuned to provide fine tuning for the operation of the respective resonating means and thus the filter.

Problems exist with the conventional form of apparatus when one considers that the filter bodies are formed from solid material which can be relatively expensive. The need to machine the same to form the filters is in itself expensive in terms of discarded material, and the machining time also increases cost. However, the need to add the transmission lines is particularly problematic as the same need to be provided in the filter body by forming the outer part trough or channel along the route of the transmission line, and then mounting the inner part of the transmission line in the outer part trough or channel. The outer part trough or channel is typically routed between and around the cavities of the resonating means, which means that the outer part trough or channel can often be formed along a relatively tortuous path due to the desire to keep the overall size of the filter body to a minimum, and thus to minimise the quantity of the material used. However, even with the use of a tortuous path, the required length and shape of the transmission line paths and/or the shape of the resonating means cavities means that the size of the filter body has to be increased to be greater than desired due to the need to accommodate the required transmission lines.

The aim of the present invention is to provide filter apparatus which allows the accommodation and the required formation of the resonating means therein, and the provision of the transmission lines for the resonating means, in a manner to reduce the material which is required to be used and/ or reduce the constraints on the design of the transmission line paths and still at least maintain, but preferably improve, the performance of the filter apparatus.

It is a further aim of the present invention to provide a method of manufacturing filter apparatus that overcomes the abovementioned problems.

In a first aspect of the invention there is provided filter apparatus, said filter apparatus including a filter body in which one or more resonating means are formed, a support member for location over at least a part of one face of the said filter body, and at least one transmission line for transmitting one or more radio frequency signals therealong in use, wherein said at least one transmission line is located on or associated with said support member.

In one embodiment at least one transmission line is connected with or to one or more of said resonating means.

Preferably two or more resonating means are provided and at least one transmission line is provided is connected with or between said two or more resonating means. In one embodiment the support member is formed of sheet material.

Preferably the support member is provided as a lid for at least part of one face of the filter body in which the resonating means are formed. Preferably the face of the filter body covered by the support member is an upper face or face in which one or more openings are defined therein.

Preferably each resonating means includes one or more cavities, channels and/ or recesses with one or more resonating structures located therein. The one or more resonating structures are arranged to resonate at a required frequency or frequency range in use.

Preferably the one or more resonating structures can include any or any combination of one or more combline resonators, one or more rods, metallic rods, ceramic rods, ceramic pucks and/ or the like.

Preferably each cavity, channel and/or recess of the resonating means has an opening defined therein. Preferably the support member typically covers a whole or substantial part of said opening of said resonating means to act as a lid or cover for said resonating means.

In one embodiment a single support member acts as a lid to substantially cover the openings of one or more, or all, of the resonating means in the filter body. In an alternative embodiment a plurality of support members can be provided to provide a lid to cover the openings of one or more or all of the resonating means of the filter body.

Typically the at least one transmission line is located on or associated with a surface of the support member which opposes a support member surface which faces towards the filter body. Thus, in one example, the support member has a first upper surface which faces outwardly of the filter body when fitted, and a second lower surface which faces inwardly of the filter body towards the resonating means when fitted. The at least one transmission line is preferably provided on the first upper surface of the support member.

In one embodiment the transmission line includes a first outer part and a second inner part. Preferably the first outer part transmission line is in the form of a trough, channel and/ or recess and is formed in a surface of the support member.

Preferably the second inner transmission line part is in the form of an electrically conductive member, material and/or strip.

Preferably the second inner transmission line part is mounted so as to be a spaced distance above or apart from a surface of the support member and/or first outer transmission line part, and preferably a spaced distance above the surface of the support member on which the transmission line is to be located with (for example, the first upper surface). Thus, the second inner transmission line part is considered to be suspended from or float above the first outer transmission line part.

In one embodiment the second inner transmission line part is spaced apart from the support member and/or first outer transmission line part by electrical insulating means so as to prevent electrical contact between the electrically conductive second inner part transmission line and the support member.

The electrical insulating means can include any or any combination of one or more insulating screws, locator bushes and/ or the like.

In one embodiment at least a portion of the support member in which the first outer transmission line part is located, is formed of and/or coated with an electrically conductive material or materials.

In one embodiment the support member is formed, at least in part, of an electrically conductive material. For example, the support member could be formed from metal. In another embodiment the support member is formed, at least in part, from a non-electrically conductive material, such as for example a printed circuit board (PCB) material. A portion of the support member which is adjacent to a transmission line path, such as for example the portion where the first outer part trough, channel or recess is defined, is coated with an electrically conductive material or materials. In a further embodiment, the support member could be formed from a combination of electrically conductive material and non-electrically conductive material.

In one embodiment, when the support member is formed of PCB material a portion of the support member which is not used for or adjacent to the one or more transmission lines can be used for other purposes, such as for example, the location of a separate active or passive electrical circuit (i.e. the electrical circuit could include one or more low noise amplifiers (LNAs), couplers, bias-Ts, control circuits and/or the like). For example, the electrical circuit components can be located between one or more tuning screws of the filter and one or more transmission lines.

Typically one or more transmission lines are connected to or between one or more of the resonating means in the filter body using transition means. The transition means are preferably one or more electrically conductive members which pass through or between the support member, the second inner transmission line part, and into connection with a resonating means at the appropriate location in the filter body.

In one embodiment the transition means include a capacitive coupling, a transformer, a direct coupling, a pin, one or more screws, solder and/or the like.

In one embodiment at least one transmission line is formed in the support member and at least another transmission line is formed in the filter body. Alternatively, the required transmission lines for the apparatus are all formed in the support member. Preferably the support member includes one or more tuning means for tuning a resonating means to a required frequency or frequency range (such as a radio frequency (RF) or RF range).

Preferably the tuning means is in the form of a tuning screw.

Preferably the tuning means and/ or tuning screw has a first portion which is exposed on the surface of the support member on which a transmission lines is mounted or associated with in accordance with the invention and substantially accessible to allow tuning of the tuning means and/ or tuning screw in use. For example, the first portion can be in the form of a head that is accessible from an upper or outer surface of the support member. Preferably the tuning means and/or tuning screw has a second portion which passes through the support member and into the respective resonating means at the required location. Preferably the second portion includes a threaded section so that the tuning means and/or tuning screw is in threaded engagement with the support member as it passes therethrough. This typically allows adjustment of the tuning means and/ or tuning screw by rotation of the first and second portions with respect to the support member.

Typically the size of the first portion of the tuning means which is located on the side of the support member on which the transmission lines are provided, is arranged so that an end or free end of the said first portion is located above the transmission line.

In one embodiment an environmental cover and/or further cover can be provided over at least part or substantially all of the support member to protect the one or more tuning screws, transmission lines, support member(s) and/or the like from environmental conditions when the apparatus is deployed in the field. For example, one or more walls can be formed on or around the support member and/or on the filter body to allow attachment of the environmental cover and/or further cover thereto. One or more attachment means could be provided to attach the environmental cover and/ or further cover to the filter body and/ or the like.

The present invention is arranged such that no extra height is required to be added to the filter apparatus as a result of the invention, as the transmission lines are located within the space defined between the upper surface of the support member and the ends of the first portions of the tuning means above the support member.

Typically the support member is engaged or mechanically engaged to the filter body to form the apparatus in accordance with the invention. The engagement means can include any or any combination of one or more screws, nuts and bolts, clips, inter-engaging members and/ or the like.

Preferably the transmission lines are all located on or associated with the same surface of the support member, such that only that surface is required to be environmentally sealed, thereby reducing cost and time in manufacture.

Typically the filter apparatus can be adapted by replacing the support member with another support member which may have a different transmission line arrangement and/or allows the support member to be repaired without the need for a new filter body to be provided.

The provision of the transmission lines on the support member rather than the filter body means that substantially the whole area of the surface of the support member is available for the formation of the transmission line paths thereon. As the support member will typically have the same surface area as the filter body surface face on which the support member is to be mounted in use, it will be appreciated that this is a considerable amount of free space. Furthermore, no more height needs to be added to the filter body as the transmission lines are placed within the gap between the upper ends of the first part of the tuning members and the support member. This is in contrast to the conventional apparatus in which only that part of the surface of the filter body in which the resonating means have not been formed is available for the transmission lines to be located.

This means that no additional width or length is required to be added to the filter body as the transmission lines can now be accommodated within the size of the filter apparatus required for the formation of the resonating means therein.

Filter apparatus referred to herein typically is for filtering one or more radio frequency signals passing therethrough. The one or more transmission lines of the filter typically allow for the passage of one or more radio frequency signals therealong to allow the resonating means and/or other RF components to be cascaded or connected together and/ or to allow one or more filters to be multiplexed together.

According to a second aspect of the present invention there is provided a method of manufacturing filter apparatus, said filter apparatus including a filter body in which one or more resonating means are formed, and at least one transmission line is provided for transmitting one or more radio frequency signals therealong in use, and wherein said method includes the step of locating a support member over at least a part of one face of the said filter body, said at least one transmission line located on or associated with said support member.

Specific embodiments of the invention are now described with reference to the accompanying drawings in which;

Figure 1 (PRIOR ART) illustrates part of a conventional filter assembly with the lid for the filter assembly removed;

Figure 2 illustrates filter apparatus in accordance with one embodiment of the invention; Figure 3 illustrates a cross section taken through part of the filter apparatus of Figure 2;

Figure 4 illustrates a transition arrangement between a transmission line and the filter body;

Figure 5 illustrates a view of a support member in accordance with another embodiment of the invention;

Figure 6 is a cross sectional view of part of the support member of Figure 5;

Figure 7 is a view of a variation of the support member in accordance with one embodiment; and

Figures 8 and 9 illustrate a detailed view of the support means for the transmission line on said support member and at the transition.

Referring firstly to Figure 1 there is illustrated part of a conventional filter assembly body A in which there is formed and shaped two filters B, C comprising a plurality of resonating means. Each filter B, C comprises a plurality of cavities with one or more upwardly protruding resonating rods located therein, and arranged to resonate at a required frequency or frequency range. The resonating rods can be formed from metal, ceramic and/ of the like.

In accordance with this conventional arrangement, transmission lines D are provided to connect the resonating means together. The transmission lines D are mounted in recesses formed in the filter body A and, as the transmission lines are mounted in the body, the paths of the same, which are required to be of specified and tightly controlled lengths, have to be routed around and between the filters B, C and/ or resonating means. It will be seen in the example shown that the need to provide the transmission lines of the required length has meant that the portion D' has had to be formed along the outside of one of the resonating means and, in order to accommodate this, the dimensions of the filter body are greater, and hence the apparatus is more expensive, than if only the resonating means were accommodated in the filter body. Once formed, the upper surface E of the filer body is enclosed by a lid (not shown).

Turning now to Figure 2, there is illustrated a first embodiment of a filter apparatus 2 in accordance with the invention. The apparatus includes a body 4 in which a plurality of resonating means are defined in a conventional manner, and therefore need not be described in further detail here. A support member 6 is provided over the openings of the resonating means cavities and the upper surface of the filter body which acts as a lid. Support member 6 is engaged to the filter body using suitable engagement means, such as one or more screws.

The support member 6 includes a plurality of tuning screws (not shown) which, again, are provided in a conventional manner and at locations which are determined by the resonating means underneath the support member. The tuning effect of the filter is achieved by selectively rotating the tuning screws so that the resonating means resonate at the required frequency or frequency range.

In accordance with the present invention, there is provided on an upper surface 8 of the support member 6, which is the surface opposing that which faces towards the filter body 4, first and second transmission lines 14, 16. Each transmission line 14, 16 is formed from an elongate strip of electrically conductive material which is provided of a required length and accommodated between the tuning screw and fixing screw locations on the upper surface 8. It will immediately be appreciated that there is considerably more space available on the upper surface 8 of the support member 6 for the location of the transmission lines than is conventionally the case on the upper surface of the filter body. Figure 3 illustrates a cross sectional view of the filter apparatus and shows part of two resonating means 10, 12 formed in the filter body. The support member 6 is located over the openings of the cavities of the resonating means 10, 12 to act as a lid to enclose the cavities of the resonating means.

It will also be seen from Figures 3 and 4 that the transmission lines 14, 16 comprise an outer trough part 20, 22 and an electrically conductive inner part that is largely suspended or floating within the outer trough part. In Figures 3 and 4 the support member 6 is formed from an electrically conductive material so the outer part troughs, which are required to be formed from electrically conductive material, can simply be machined in the support member 6 to form the required transmission line paths.

Turning now to Figures 5 and 6 there is again shown a member 6 in which the transmission line outer part troughs 20, 22 are formed for the location of transmission lines (not shown) therewith. In this case the support member 6 is formed from PCB material which is not electrically conductive, but in order to allow the correct operation of the transmission lines at least the external surface area of the outer part troughs 20, 22 are coated with a conductive material, 18 typically by undertaking a plating process. In addition, in this embodiment, the remainder of the surface of the support member 6 in which transmission lines are not provided is then available for the location and formation of other electric circuits and/or electric components thereon, thereby further increasing the utility of the support member.

Figure 7 illustrates a further arrangement of a PCB support member in which, while it is still ensured that the inner part of the transmission line (not shown) is not in contact with any conductive material connected to the external face of the outer part troughs 20, 22 of the respective transmission lines, it can still be possible to have a conductive area on another part of the support member 6 that is not connected to the outer part troughs 20, 22 of the transmission line. In this case the inner parts of the transmission line can be connected to the additional conductive areas using bridge portions 25 which are located as required and which straddle the troughs 20, 22. The bridge portions in this embodiment are formed from electrical insulating material, such as for example, PCB material. The inner part of the transmission line rests on the bridge portion 25 and can be soldered to a metallised/plated part of the bridge to hold the same in place. The metallised area of the bridge is electrically isolated from the outer trough 20, 22 as there is a space between the metal surfaces.

As previously stated, the inner part of the transmission lines are required to be kept floating and out of contact with the conductive material of, or coated on, the outer part troughs of the transmission line and one arrangement of achieving this is shown in Figures 8 and 9. In Figure 9 the transmission line inner part 16 is shown as being mounted above the transmission line outer part trough 22 by insulated screws 24 and locator bush 26. It is also shown how the transmission line inner part 16 is spaced from below and to the sides from the outer part trough 22.

Figure 8 illustrates an arrangement which allows the transition and connection between the transmission line inner part 16 and resonating cavity 10 in accordance with the invention. The transmission line inner part 16 is connected via a pin 28 which passes through the support member 6 (not shown) and into the filter body 4 via a transformer 30 formed in the body 4 and is located with the resonating means 10 to achieve connection with the same.

There is therefore provided a filter apparatus in accordance with the invention which allows the required filter performance to be achieved with reduced requirements for material usage.

Claims

1. Filter apparatus, said filter apparatus including a filter body in which one or more resonating means are formed, a support member for location over at least a part of one face of the said filter body, and at least one transmission line for transmitting one or more radio frequency signals therealong in use, wherein said at least one transmission line is located on or associated with said support member.

2. Filter apparatus according to claim 1 wherein at least one transmission line is connected with or to one or more of said resonating means.

3. Filter apparatus according to claim 1 wherein two or more resonating means are formed and at least one transmission line is connected with or between two or more of said resonating means.

4. Filter apparatus according to claim 1 wherein the support member is formed of sheet material.

5. Filter apparatus according to claim 1 wherein each of said one or more resonating means includes a cavity, channel and/or recess with an opening defined therein, the support member covering a whole or substantial part of said opening or openings.

6. Filter apparatus according to claim 5 wherein a resonating structure is formed or provided in said cavity, channel and/or recess, said resonating structure in the form of any or any combination of one or more combline resonators, one or more rods, metallic rods, ceramic rods or ceramic pucks.

7. Filter apparatus according to claim 1 wherein the at least one transmission line is located on or associated with a surface of the support member that opposes a support member surface facing towards the filter body.

8. Filter apparatus according to claim 1 wherein the at least one transmission line includes a first outer part in the form of a trough, channel and/or recess formed in a surface of the support member, and a second inner part in the form of an electrically conductive member, material and/ or strip.

9. Filter apparatus according to claim 8 wherein the second inner transmission line part is mounted so as to be a spaced distance above or apart from a surface of the support member and/ or the first outer transmission line part.

10. Filter apparatus according to claim 9 wherein electrical insulating means are provided to space the second inner transmission line part from the support member and/ or first outer transmission line part.

11. Filter apparatus according to claim 10 wherein the electrical insulating means include any or any combination of one or more insulating screws or bushes.

12. Filter apparatus according to claim 8 wherein at least a portion of the support member in which the first outer transmission line part is located, is formed of and/or coated with an electrically conductive material or materials.

13. Filter apparatus according to claim 1 wherein the support member is formed, at least in part, of an electrically conductive material or metal.

14. Filter apparatus according to claim 1 wherein the support member is formed, at least in part, from a non-electrically conductive material or printed circuit board (PCB) material.

15. Filter apparatus according to claim 14 wherein a portion of the PCB material from which the support member is formed which is not used for or adjacent the one or more transmission lines is used for the location of a separate active or passive electric circuit and/or electrical components.

16. Filter apparatus according to claim 1 wherein the one or more transmission lines are connected to or between one or more of the resonating means in the filter body using transition means.

17. Filter apparatus according to claim 16 wherein the transition means are one or more electrically conductive members which pass through or between the support member, the second inner transmission line part and into connection with the resonating means.

18. Filter apparatus according to claim 16 wherein the transition means include a capacitive coupling, a direct coupling, one or more screws, a transformer, pin and/ or solder.

19. Filter apparatus according to claim 1 wherein at least one transmission line is formed in the support member and at least another transmission line is formed in the filter body.

20. Filter apparatus according to claim 1 wherein the required transmission lines for the filter apparatus are all formed in the support member.

21. Filter apparatus according to claim 1 wherein the support member includes one or more tuning means for tuning the resonating means to a required frequency or frequency range.

22. Filter apparatus according to claim 21 wherein the one or more tuning means includes a first portion which is exposed on the surface of the support member on which the transmission lines are mounted or associated therewith to allow tuning of the tuning means in use.

23. Filter apparatus according to claim 22 wherein the one or more tuning means includes a second portion which passes through the support member and into the resonating means.

24. Filter apparatus according to claim 23 wherein the second portion includes a threaded section so that the second portion is in threaded engagement with the support member and allows adjustment of the tuning means by rotation of the second portion with respect to the support member.

25. Filter apparatus according to claim 22 wherein an end or free end of the first portion of the tuning means is located on the side of the support member on which the transmission lines are provided and above the transmission lines.

26. Filter apparatus according to claim 1 wherein an environmental cover is provided over at least part, or substantially all, of the support member.

27. Filter apparatus according to claim 1 wherein one or more walls are formed on the support member and/or filter to allow attachment of the environmental cover thereto.

28. Filter apparatus according to claim 1 wherein the support member is engaged to the filter body using engagement means.

29. Filter apparatus according to claim 28 wherein the engagement means can include any or any combination of one or more screws, nuts and bolts or inter-engaging members.

30. Filter apparatus according to claim 1 wherein the transmission lines are all located on or associated with the same surface of the support member.

31. A method of manufacturing filter apparatus, said filter apparatus including a filter body in which one or more resonating means are formed, and at least one transmission line for transmitting one or more radio frequency signals therealong in use, and wherein said method includes the step of locating a support member over at least a part of one face of the said filter body, said at least one transmission line located on or associated with said support member.