WO2020030249A1

WO2020030249A1 - Radio frequency radio-frequency apparatus and components thereof

Info

Publication number: WO2020030249A1
Application number: PCT/EP2018/071362
Authority: WO
Inventors: Florian Pivit
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2018-08-07
Filing date: 2018-08-07
Publication date: 2020-02-13
Anticipated expiration: 2021-02-07
Also published as: CN112772010A

Abstract

An apparatus comprising:a conductive housing comprising conductive housing walls that a least partially enclose a cavity; a printed circuit board adjacent the conductive housing walls forming a cover of the cavity that is directly adjacent the cavity; and a stress relief element between the conductive housing walls and the printed circuit board, wherein the combination of the conductive housing walls, the stress relief element and the printed circuit board creates an enclosed cavity of a resonant cavity filter.

Description

TITLE

Radio frequency radio-frequency apparatus and components thereof.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to radio frequency apparatus and components thereof. In particular, at some relate to higher integration within radio frequency apparatus, such as a base station.

BACKGROUND

It is desirable to achieve higher integration within radio frequency apparatus, particularly a base station, that reduces the requirements for screws, coaxial connectors, jumper cables etc.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: conductive housing walls that a least partially enclose a cavity; a stress relief element positioned where the conductive housing walls attach to a printed circuit board, wherein the combination of the conductive housing walls, the stress relief element and the printed circuit board creates an enclosed cavity for a resonant cavity filter.

In at least some examples, the stress relief element is configured to deform to absorb stress.

In at least some examples, the stress relief element has a repeated pattern.

In at least some examples, the stress relief element is conductive.

In at least some examples, the stress relief element is a wall structure.

In at least some examples, the wall structure meanders.

In at least some examples, the wall structure is shaped into a series of parallel ridges and grooves. In at least some examples, the wall structure is an integral part of the housing wall or the wall structure is attached to the housing wall.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising:

a conductive housing comprising conductive housing walls that a least partially enclose a cavity;

a printed circuit board adjacent the conductive housing walls forming a cover of the cavity that is directly adjacent the cavity; and

a stress relief element between the conductive housing walls and the printed circuit board,

wherein the combination of the conductive housing walls, the stress relief element and the printed circuit board creates an enclosed cavity of a resonant cavity filter.

In at least some examples, the stress relief element has a repeated pattern.

In at least some examples, the stress relief element is conductive.

In at least some examples, the stress relief element directly connects the housing walls and a perimeter of the printed circuit board.

In at least some examples, the stress relief element extends around the whole of a perimeter of the printed circuit board.

In at least some examples, the stress relief element is a wall structure.

In at least some examples, the wall structure extends in a height-wise direction from the housing to the printed circuit board and is sufficiently stiff in that direction to keep the printed circuit board at a fixed displacement, in that direction, from the housing. In at least some examples, the wall structure has a thickness in a lateral direction parallel to a plane of the printed circuit board and wherein the wall structure extends from the housing to the printed circuit board a first distance greater than the thickness.

In at least some examples, the wall structure has a length that is greater than a length of a perimeter of the printed circuit board where the wall structure attaches to the PCB.

In at least some examples, the wall structure meanders.

In at least some examples, the wall structure is shaped into a series of parallel ridges and grooves

In at least some examples, the wall structure is an integral part of the housing wall or the wall structure is attached to the housing wall.

According to various, but not necessarily all, embodiments there is provided a printed circuit board for use in a resonant cavity filter, comprising: at least one conductive substrate; at least one user tunable device for tuning a resonant cavity filter, formed by attaching the printed circuit board to conductive housing walls, that a least partially enclose a cavity, to create an enclosed cavity for the resonant cavity filter, wherein the at least one user tunable device is configured to be varied by a user to tune the resonant cavity filter.

According to various, but not necessarily all, embodiments there is provided a frequency selective radio-frequency apparatus comprising:

a conductive component;

a printed circuit board adjacent the conductive component; and

a conductive stress relief element between the conductive component and the printed circuit board,

wherein the combination of the conductive component, the conductive stress relief element and the printed circuit board creates a conductive portion of the frequency selective radio-frequency apparatus In at least some examples, the frequency selective radio-frequency component is a cavity filter or an antenna.

According to various, but not necessarily all, embodiments there is provided a conductive component of a frequency selective radio-frequency apparatus comprising: a conductive stress relief element positioned where the conductive component attaches to a printed circuit board, wherein the combination of the conductive stress relief element, the conductive component and the printed circuit board creates a conductive portion of the frequency selective radio-frequency apparatus.

According to various, but not necessarily all, embodiments there is provided a printed circuit board for use in a frequency selective radio-frequency apparatus comprising: at least one conductive substrate;

at least one user tunable device for tuning a frequency selective radio frequency apparatus formed by attaching the printed circuit board to a conductive component of the frequency selective radio-frequency apparatus to form a conductive portion of the frequency selective radio-frequency apparatus, wherein the at least one user tunable device is configured to be varied by a user to control an electrical impedance associated with the conductive portion.

The above examples can be used to I reduce a cost and/or weight of the apparatus or components. In at least some examples, a bulky passive metal component (the filter housing) is mechanically and electrically connected to an active part of transceiver (based on Printed Circuit Technology) by a more cost-efficient method than currently used.

In radio frequency systems, such as base stations, frequency-selective components are used. Sometimes the frequency selectivity arises from an electrical length of a component, which determines a resonant wavelength. Arbitrarily changing the dimensions or arrangement of components could change their electrical length, negatively impacting on operation, and is not therefore always possible. Also, the frequency selectivity can arise from complex electrical impedances that depend upon the relative positioning of electrical components. It is therefore important that such components have controlled relative positioning so that the frequency selectivity is reliable. According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

Some example embodiments will now be described with reference to the accompanying drawings in which:

FIG. 1 shows an example embodiment of the subject matter described herein;

FIG. 2 shows another example embodiment of the subject matter described herein; FIG. 3 shows another example embodiment of the subject matter described herein; FIG. 4 shows another example embodiment of the subject matter described herein; FIG. 5 shows another example embodiment of the subject matter described herein; FIG. 6 shows another example embodiment of the subject matter described herein.

DETAILED DESCRIPTION

FIG 1 illustrates an example of an apparatus 100. The apparatus 100 is a frequency selective radio-frequency apparatus 100. It is frequency-selective in that it is configured to operate at some frequencies but not at other frequencies. For example, it may have bandpass characteristics at one or more frequency ranges.

The apparatus 100 may, for example, be a filter such as a resonant cavity filter, or an antenna. A resonant cavity filter is a filter with one or more resonant cavities. In some but not necessarily all examples a cavity of a resonant cavity filter can comprise resonators. Examples of resonators include metallic resonators and dielectric resonators.

The apparatus 100 comprises a printed circuit board (PCB) 10, a conductive structure 20; and a stress relief element 50 as an interface between the conductive component 20 and the printed circuit board 10. The combination of at least the conductive component 20 and the printed circuit board 10 creates a conductive portion of the frequency selective radio-frequency apparatus 100.

In the example illustrated in FIG 1 , the frequency selective radio-frequency apparatus 100 is a resonant cavity filter, shown in cross-section. The conductive structure 20 is a conductive housing 20 that has conductive housing walls 22 at least partially defining a cavity 24.

The printed circuit board (PCB) 10 provides connections in a predetermined arrangement on a common substrate. In some but not necessarily all examples, the PCB 10 is designed to have an effect on circuit operation other than just point to point connection. In some but not necessarily all examples, the PCB 10 comprises active and/or passive components 1 1 . These components may be embedded in the PCB 10, for example by printing, or mounted on the PCB 10, for example by soldering. A PCB 10 with active and/or passive components may be referred to as a printed circuit board assembly. The PCB 10 mechanically supports and electrically connects the components.

In some but not necessarily all examples, a substrate 12 of the PCB 10 comprises an electrically isolated conductive sheet. The sheet may be formed from metal foil such as copper. Conductive tracks, pads and other features are etched from or onto the sheet. A multi-layer PCB 10 comprises electrically isolated conductive sheets and features of one sheet may be interconnected to features of another sheet.

The substrate 12 therefore provides both electrical connection and mechanical support. The substrate 12 may, for example, comprise a glass-reinforced epoxy laminate such as, for example, FR4, and one or more conductive layers, for example copper layers.

In some but not necessarily all examples, the PCB 10 comprises components of a radio transceiver, for example receiver circuitry and/or transmitter circuitry and/or active antenna circuitry and/or measurement circuitry for measuring transceiver performance.

In this illustrated example, the printed circuit board 10 is configured for use in a resonant cavity filter 100 and comprises one or more user-tunable devices 14 for tuning the resonant cavity filter 100.

The resonant cavity filter 100 is formed by attaching the printed circuit board 10 to the conductive housing walls 22 of the housing 20. The conductive housing walls 22 partially enclose a cavity 24 when the PCB 10 is not attached and enclose the cavity 24 when the PCB 10 is attached. The enclosed cavity 24 is a void comprising dielectric, for example air, and forms a resonant cavity for the resonant cavity filter 100. The PCB 10 forms a cover of the cavity 24.

The one or more user-tunable devices 14 are configured to be varied by a user to tune the resonant cavity filter 100. In some but not necessarily all examples a user-tunable device 14 is a conductive element that extends, by a variable amount, into the cavity 24. In some but not necessarily all examples the user-tunable device 14 is a tuning screw that is rotated in a first sense to move into the cavity 24 and is rotated in a second, opposite, sense to move out of the cavity 24. The PCB 10 forms a tuning cover of the cavity 24

The housing 20 is conductive. It forms with the attached PCB 10 a conductive enclosure for the cavity 24. In some, but not necessarily all examples, the conductivity of the housing 20 arises from using metal, for example aluminum. In some, but not necessarily all examples, the housing 20 is formed from metal, for example, by milling or casting.

The attachment between the PCB 10 and the walls 22 of the housing 20 may be formed in any suitable manner. For example, using soldering or screws. The PCB 10 is attached and supported only at a perimeter 16 of the PCB 10, so that the PCB 10 is directly adjacent the cavity 24. The resonant cavity filter 100 is a single assembly having an integrated printed circuit board 10 and housing 20. The PCB 10 has completely replaced the solid metallic cover used to enclose the cavity in current commercially available resonant cavity filters.

FIG 1 illustrates an example of an apparatus 100 comprising: a conductive housing 20 comprising conductive housing walls 22 that a least partially enclose a cavity 24; a printed circuit board 10 adjacent the conductive housing walls 22 forming a cover of the cavity 24 that is directly adjacent the cavity 24; and a stress relief element 50 between the conductive housing walls 22 and the printed circuit board 10, wherein the combination of the conductive housing walls 24, the stress relief element 50 and the printed circuit board 10 creates a resonant cavity 24 of a resonant cavity filter 100.

Examples of stress relief element 50 are illustrated in FIGs 2 to 5.

In some but not necessarily all examples, the stress relief element provides an electrically conductive, galvanic (DC) connection all around to provide a complete conductive enclosure towards the outside. This prevents electromagnetic energy entering or leaving the cavity as well as providing a physical barrier preventing ingress of dirt, moisture etc into the cavity. In some but not necessarily all examples, the stress relief element 50 provides a hermetic (airtight) seal between PCB 10 and housing walls 22. In some but not necessarily all examples, the stress relief element 50 is a thin and solid wall.

Fig 2 illustrates, in a three-dimensional perspective view, an example of a housing 20 with stress relief element 50 attached using solder 70. The stress relief element 50 is substantially two-dimensional. It is a wall structure 54 that is substantially thinner, laterally, than the housing wall 22. The wall structure 54 extends in a loop around the whole of the opening of the cavity 24 and the central void it creates forms an extension to the cavity 24.

Figs 3 and 4 illustrate, from a top-perspective view, different examples of a stress relief element 50 attached on top of the housing wall 22. The stress relief elements 50 are substantially two-dimensional. They are wall structures 54 that is substantially thinner, laterally, than the housing wall 22. The wall structures 54 are not straight and follow a bent path. The path is curved in FIG 3 and zig-zag in FIG 4.

FIG 5 illustrates, in cross-section, an example of an apparatus 100 comprising: a conductive housing 20 comprising conductive housing walls 22 that a least partially enclose a cavity 24; a printed circuit board 10 adjacent the conductive housing walls 22 forming a cover of the cavity 24 that is directly adjacent the cavity 24; and a stress relief element 50 between the conductive housing walls 22 and the printed circuit board 10. The combination of the conductive housing walls 24, the stress relief element 50 and the printed circuit board 10 creates a cavity 24 of a resonant cavity filter 100. The PCB 10 may comprise one or more components 1 1 and/or one or more tuning devices 14.

In the examples illustrated in FIGs 1 to 5, the stress relief element 50 modifies the interface between printed circuit board 10 and the housing 20. The stress relief element 50 allows different parts such as the housing 20 and the PCB 10 to expand/contract at different rates without excess stress being generated.

In some but not necessarily all examples the stress relief element 50 is configured to deform to absorb stress and prevent stress propagation.

In some but not necessarily all examples, stress relief element 50 is conductive. The combination of the conductive housing walls 24, a conductive substrate 12 of the printed circuit board 10 and the conductive stress relief element 50 creates a conductive enclosure for the cavity 24 of the resonant cavity filter 100.

In some but not necessarily all examples, the stress relief element 50 connects the housing walls 22 and a perimeter 16 of the printed circuit board 10. The stress relief element 50 can, in some examples, extend around the whole of a perimeter of the housing walls 22 The stress relief element 50 can, in some examples, extend around the whole of a perimeter 16 of the printed circuit board 10 (when the PCB 10 is attached).

In some but not necessarily all examples, the stress relief element 50 directly connects the housing walls 22 and a perimeter 16 of the printed circuit board 10. There is no intermediary layer between stress relief element 50 and the perimeter 16 of the printed circuit board 10 except perhaps material used to join the stress relief element 50 and the perimeter 16 such as adhesive or solder 70.

The stress relief element 50 may, in some examples be soldered in place to the housing and/or the PCB 10, as illustrated in FIG 5.

In the examples illustrated in FIGs 2 to a 5, but not necessarily all examples, the stress relief element 50 is wall structure 54. The wall structure 54 extends in a height-wise direction from the housing 20 towards the printed circuit board 10 (when attached) and is sufficiently stiff in that direction to keep the printed circuit board 10 (when attached) at a fixed displacement, in that direction, from the housing 20.

The wall structure 54 has a thickness in a lateral direction parallel to a plane of the printed circuit board 10 (when attached). The wall structure 54 is substantially thinner than a lateral thickness of the housing wall 22. The wall structure has a height extending from the housing 20 to the printed circuit board 10 (when attached) that is a first distance greater than a lateral thickness of the wall structure 54. The first distance is selected to provide sufficient deformity to capture the stress. The thinner (smaller the lateral thickness) the meandering wall is, the lower (smaller first distance) it can be, and the more sensitive it will become.

The wall structure 54 accommodates lateral stress but is stiff vertically (height-wise), This avoids de-tuning of the frequency selectivity.

The wall structure 54 in the examples illustrated, but not necessarily all examples, is a solid wall that provides a physical barrier and an electrical shield.

In the examples illustrated in FIGs 2 to 5, but not necessarily all examples, the wall structure 54 has a length that is greater than a length of a perimeter 16 of the printed circuit board 10 where the wall structure 54 attaches to the PCB 10. The wall structure 54 therefore needs to have some bends.

In the examples illustrated in FIG 2, the wall structure 54 meanders laterally. As illustrated in FIG 3 the meandering can be a soft or undulating meander with curved bends. As illustrated in FIG 4 the meandering can be harder with sharp bends creating a concertina effect.

In the examples of FIGs 2, 3 and 4 the wall structure 54 is shaped into a series of parallel ridges and grooves that are parallel to a height-wise axis that is orthogonal to a plane of the PCB 10 (when attached). In this example they are parallel to the walls 22 of the housing. The corrugation/meanders of the stress relief element 50 can have a regular, repeated pattern. For example, the parallel ridges may be separated by first distances and the parallel grooves may be separated by second distances. In some examples the first distances may be substantially the same and the second distances may be substantially the same. In some examples the first distances and the second distances may be substantially the same. .

In the examples of FIG 2 and 5 the wall structure 54 is attached to the housing wall 22, for example, by screws, solder 70, crimping or adhesive. A similar approach could be used for the examples of FIGs 3 and 4.

In the examples of FIG 3 and 4, the wall structure 54 is an integral part of the housing wall 22. It may be milled or cast into the housing wall 22. A similar approach could be used for the example of FIGs 1 and 5.

In this example of FIG 5, the printed circuit board 10 has been soldered 70 to the stress relief element 50. However, other attachments may be used.

In the examples illustrated in FIGs 2, 3 and 4 the stress relief element 50 is part of the housing 20 before the PCB 10 is attached. Such an arrangement is also possible in other examples.

The housing apparatus 20 consequently comprises: conductive housing walls 22 that a least partially enclose a cavity 24; and a stress relief element 50 positioned where the conductive housing walls 22 would attach to a printed circuit board 10 when assembled thereto.

The combination of the conductive housing walls 22, the stress relief element 50 and the printed circuit board 10 (when attached) creates an enclosed cavity for a resonant cavity filter 100. The stress relief element 50 extends from the housing wall 22 and is configured for attaching the housing walls 22 to the printed circuit board 10.

The printed circuit board 10 comprises: at least one conductive substrate; at least one user tunable device 14 for tuning a resonant cavity filter 100, formed by attaching the printed circuit board 10 to the conductive housing walls 22, that at least partially enclose a cavity 24. This combination of PCB 10 and housing 22 including the stress relief element 50, creates an enclosed cavity 24 for the resonant cavity filter 100. The at least one user tunable device 14 is configured to be varied by a user to tune the resonant cavity filter 100.

The stress relief element 50 in the previously described examples of FIGs 1 to 5, reduces the adverse effects arising from different coefficients of thermal expansion between the housing 20 and PCB 10. The stress relief element 50 enables the printed circuit board 10 to be used as a filter cover and enables a new type of housing with printed circuit board 10 as cover, and a new type of printed circuit board 10.

In some, but not necessarily all examples, the PCB 10 is attached to the housing 20 using solder . The combination of the PCB 10 and housing 20 with stress relief element 50 is fused together using solder paste in a reflow chamber, which may be at a temperature greater than 200°C. The solder 70, the PCB 10 and housing 20, and in some circumstances the stress relief element 50, form a resonant cavity filter 100 having a homogeneous conductive enclosure of the resonant cavity 24. The stress relief element 50 prevents excessive stress developing in the PCB 10, as a consequence of different coefficients of thermal expansion, as the resonant cavity filter 100 cools.

In the example illustrated in FIG 6, the resonant cavity filter 100 as previously described, is a part of a base transceiver station 200. The filter is low cost and low mass.

The cavity filter 100 may, for example, operate as a diplexer or triplexer.

The cavity filter 100 may, for example, provide components of a passive or active antenna system. An active antenna is an antenna that contains active electronic components such as transistors. These may be provided by the PCB 10.

In the preceding examples a cavity filter 100 was created by combining a housing 20 and a PCB 10, while using stress relief element 50 to control stress. However, in other examples a different frequency selective radio-frequency component 100 may be created, such as an antenna.

The frequency selective radio-frequency apparatus 100 comprises: a conductive component 20; a printed circuit board 10 adjacent the conductive component 20; and a conductive stress relief element 50 between the conductive component 20 and the printed circuit board 10, wherein the combination of at least the conductive component 20, the stress relief element 50 and the printed circuit board 10 creates a conductive portion of the frequency selective radio-frequency apparatus 100.

In some examples, but not necessarily all examples, the conductive component of the frequency selective radio-frequency apparatus 100 comprises before attachment to the PCB 10: a conductive stress relief element 50 positioned where the conductive component 20 attaches to a printed circuit board 10, wherein the combination of the conductive stress relief element 50, the conductive component 20 and the printed circuit board 10 (when attached) creates a conductive portion of the frequency selective radio-frequency apparatus 100.

In some examples, but not necessarily all examples, the printed circuit board 10 for use in a frequency selective radio-frequency apparatus 100 comprises: at least one conductive substrate 12; at least one user tunable device 14 for tuning a frequency selective radio frequency apparatus 100 formed by attaching the printed circuit board 10 to a conductive component 20 of the frequency selective radio-frequency apparatus100 to form a conductive portion of the frequency selective radio-frequency apparatus 100, wherein the at least one user tunable device 14 is configured to be varied by a user to control an electrical impedance associated with the conductive portion.

As used in this application, the term‘circuitry’ may refer to one or more or all of the following:

(a) hardware-only circuitry implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable):

(i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile apparatus or a similar integrated circuit in a server, a cellular network apparatus, or other computing or network apparatus.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

The frequency selectivity of a frequency selective radio-frequency apparatus 100 means that it is configured to operate in one or more of a plurality of operational resonant frequency bands. For example, the operational frequency bands may include (but are not limited to) Long Term Evolution (LTE) (US) (734 to 746 MHz and 869 to 894 MHz), Long Term Evolution (LTE) (rest of the world) (791 to 821 MHz and 925 to 960 MHz), amplitude modulation (AM) radio (0.535-1.705 MHz); frequency modulation (FM) radio (76-108 MHz); Bluetooth (2400-2483.5 MHz); wireless local area network (WLAN) (2400-2483.5 MHz); hiper local area network (HiperLAN) (5150-5850 MHz); global positioning system (GPS) (1570.42-1580.42 MHz); US - Global system for mobile communications (US-GSM) 850 (824-894 MHz) and 1900 (1850 - 1990 MHz); European global system for mobile communications (EGSM) 900 (880-960 MHz) and 1800 (1710 - 1880 MHz); European wideband code division multiple access (EU- WCDMA) 900 (880-960 MHz); personal communications network (PCN/DCS) 1800 (1710-1880 MHz); US wideband code division multiple access (US-WCDMA) 1700 (transmit: 1710 to 1755 MHz , receive: 21 10 to 2155 MHz) and 1900 (1850-1990 MHz); wideband code division multiple access (WCDMA) 2100 (transmit: 1920-1980 MHz, receive: 21 10-2180 MHz); personal communications service (PCS) 1900 (1850-1990 MHz); time division synchronous code division multiple access (TD-SCDMA) (1900 MHz to 1920 MHz, 2010 MHz to 2025 MHz), ultra wideband (UWB) Lower (3100-4900 MHz); UWB Upper (6000-10600 MHz); digital video broadcasting - handheld (DVB-H) (470-702 MHz); DVB-H US (1670-1675 MHz); digital radio mondiale (DRM) (0.15-30 MHz); worldwide interoperability for microwave access (WiMax) (2300-2400 MHz, 2305-2360 MHz, 2496-2690 MHz, 3300-3400 MHz, 3400-3800 MHz, 5250-5875 MHz); digital audio broadcasting (DAB) (174.928-239.2 MHz, 1452.96- 1490.62 MHz); radio frequency identification low frequency (RFID LF) (0.125-0.134 MHz); radio frequency identification high frequency (RFID HF) (13.56-13.56 MHz); radio frequency identification ultra high frequency (RFID UHF) (433 MHz, 865-956 MHz, 2450 MHz).

An operational frequency band is a frequency range over which an apparatus can efficiently operate. It may be defined as a frequency range where the apparatus’ return loss (reflection coefficient) is less than an operational threshold dependent upon application.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to“comprising only one” or by using“consisting”.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term‘example’ or‘for example’ or‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus‘example’, ‘for example’, ‘can’ or‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although embodiments have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

The term ‘a’ or‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use‘a’ or‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer and exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature) or combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The use of the term‘example’ or‘for example’ or‘can’ or‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus‘example’,‘for example’, ‘can’ or‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon. l/we claim:

Claims

1 . An apparatus comprising:

conductive housing walls that a least partially enclose a cavity;

a stress relief element positioned where the conductive housing walls attach to a printed circuit board, wherein the combination of the conductive housing walls, the stress relief element and the printed circuit board creates an enclosed cavity for a resonant cavity filter.

2. An apparatus as claimed in claim 1 , wherein the stress relief element is configured to deform to absorb stress.

3. An apparatus as claimed in claim 1 or 2, wherein the stress relief element has a repeated pattern.

4. An apparatus as claimed in claim 1 , 2 or 3, wherein the stress relief element is conductive.

5. An apparatus as claimed in any of claims 1 to 4, wherein the stress relief element is a wall structure.

6. An apparatus as claimed in any of claims 1 to 5, wherein the wall structure meanders.

7. An apparatus as claimed in any of claims 1 to 6, wherein the wall structure is shaped into a series of parallel ridges and grooves.

8. An apparatus as claimed in any of claims 1 to 7, wherein the wall structure is an integral part of the housing wall or the wall structure is attached to the housing wall.

9. An apparatus comprising:

a printed circuit board adjacent the conductive housing walls forming a cover of the cavity that is directly adjacent the cavity; and a stress relief element between the conductive housing walls and the printed circuit board,

wherein the combination of the conductive housing walls, the stress relief element and the printed circuit board creates an enclosed cavity of a resonant cavity filter .

10. An apparatus as claimed in claim 9, wherein the stress relief element directly connects the housing walls and a perimeter of the printed circuit board.

1 1 . An apparatus as claimed in claim 9 or 10, wherein the stress relief element extends around the whole of a perimeter of the printed circuit board.

12. An apparatus as claimed in any of claims 9 to 1 1 , wherein the stress relief element is a wall structure.

13. An apparatus as claimed in claim 12, wherein the wall structure extends in a height- wise direction from the housing to the printed circuit board and is sufficiently stiff in that direction to keep the printed circuit board at a fixed displacement, in that direction, from the housing and/or wherein the wall structure has a thickness in a lateral direction parallel to a plane of the printed circuit board and wherein the wall structure extends from the housing to the printed circuit board a first distance greater than the thickness.

14. An apparatus as claimed in claim 12 or 13, wherein the wall structure has a length that is greater than a length of a perimeter of the printed circuit board where the wall structure attaches to the printed circuit board.

15. An apparatus as claimed in any of claims 12 to 14, wherein the wall structure meanders.

16. An apparatus as claimed in any of claims 12 to 15, wherein the wall structure is a continuous conductive structure that hermetically seals the cavity.

17. An apparatus as claimed in any of claims 12 to 16, wherein the wall structure is an integral part of the housing wall or the wall structure is attached to the housing wall.

18 A printed circuit board for use in a resonant cavity filter, comprising: at least one conductive substrate;

at least one user tunable device for tuning a resonant cavity filter, formed by attaching the printed circuit board to conductive housing walls, that a least partially enclose a cavity, to create an enclosed cavity for the resonant cavity filter, wherein the at least one user tunable device is configured to be varied by a user to tune the resonant cavity filter.

19. A frequency selective radio-frequency apparatus comprising:

a conductive component;

a printed circuit board adjacent the conductive component; and

wherein the combination of the conductive component, the conductive stress relief element and the printed circuit board creates a conductive portion of the frequency selective radio-frequency apparatus

20. A conductive component of a frequency selective radio-frequency apparatus comprising:

a conductive stress relief element positioned where the conductive component attaches to a printed circuit board, wherein the combination of the conductive stress relief element, the conductive component and the printed circuit board creates a conductive portion of the frequency selective radio-frequency apparatus.