EP3311445A1

EP3311445A1 - Tunable rf cavity filter

Info

Publication number: EP3311445A1
Application number: EP16728038.7A
Authority: EP
Inventors: Mikael RITSCHER
Original assignee: Microdata Telecom Innovation Stockholm AB
Current assignee: Kaelus AB
Priority date: 2015-06-18
Filing date: 2016-06-10
Publication date: 2018-04-25
Anticipated expiration: 2036-06-10
Also published as: WO2016202687A1; CN208959338U; EP3311445B1

Abstract

In embodiments, there is provided a radio frequency (RF) cavity filter (100), comprising a housing enclosing at least one radio frequency (RF) cavity resonator (120). Each radio frequency (RF) cavity resonator (120) comprises a cavity body (130) having a cavity body axis (1303) and an inner wall (1301) around a cavity hole (1107), wherein the cavity body (130) is arranged so that its inner wall (1301) is accessible from the outside of the housing; a dielectric socket (140) comprising a lining member (1402), wherein the lining member (1402) is arranged within the cavity body (130) so that it lines the inner wall (1301) of the cavity body (130) and is exchangeable from the outside of the housing; and a tuning element (150), arranged within the dielectric socket (140) so that galvanic insulation between the inner wall (1301) and the tuning element (150) is obtained and generation of passive inter-modulation is reduced. The tuning element (150) is arranged to be accessible from the outside of the housing so that its position along the cavity body axis (1303) can be adjusted, whereby the radio frequency (RF) cavity filter (100) is tuned to frequencies dependent on the position of the tuning element (150) along the cavity body axis (1303).

Description

TUNABLE RF CAVITY FILTER

TECHNICAL FIELD

The present disclosure relates to tunable radio frequency (RF) cavity filters.

BACKGROUND

Tunable radio frequency (RF) cavity filters, also referred to as tunable radio frequency (RF) cavity resonator filters, are widely used in engineering for filtering, e.g. combiners, splitters and filters in telecommunication applications. They are typically based on a component referred to as RF cavity resonator, or just cavity resonator, comprising a cavity body. The filters are generally designed by combining a

plurality of coupled cavity resonators, where each cavity resonator is tuned to a particular frequency to achieve a combined filter

characteristic, and is typically enclosed in a chassis. A cavity

resonator can be tuned to a given frequency or given frequencies by changing the volume of the cavity body comprised in the cavity resonator, e.g. by changing the diameter of inner and outer walls of the cavity body, or by inserting tuning elements, e.g. tuning screws or other suitable objects, into the cavity body. The cavity resonators within the chassis are coupled to each other and will interact to form a resulting filter characteristic acting on an input signal to generate an output signal. The coupling between coupled cavity resonators can be controlled or regulated, e.g. by changing the relative distance between them or by introducing coupling elements between pairs of cavity resonators.

A problem with passive RF devices, such as cavity filters, is Passive Inter odulation (PI ) degrading the performance of the filter. PI is typically a result of multiple high power tones mixing at device

nonlinearities , e.g. due to manufacturing defects such as metal flakes or shavings inside the chassis, or inconsistent contact between component surfaces, for example between the surfaces of a metal tuning screw and a cavity body.

EP1987563 relates to a cavity filter comprising at least one tuning conductor presenting a hollow portion, an isolation device for a tuning conductor of a cavity filter, and a node in a mobile communications network, comprising a cavity filter. The tuning conductor comprises an isolation device in a non-conductive material, which isolation device is at least partly inserted into the hollow portion, and an insertion element in a conductive material presenting a male thread that is engaged with an inner surface of the isolation device.

PROBLEMS WITH THE PRIOR ART

In the cavity filter described in EP1987563, the insertion element presents a male thread that is engaged with an inner surface of the isolation device. Since the isolation device is made of plastic, the male thread may damage the inner surface of the isolation device during tuning and retuning of the cavity filter, so that the engaging of the insertion element with the isolation device may become less exact. If this happens, the isolation device should be replaced, so that an exact tuning of the cavity filter remains possible. However, in order to replace the

isolation device of EP1987563, the filter chassis must be opened, since the isolation device and the insertion element are inserted from the inside of the filter chassis.

There is a need for an improved tunable radio freguency (RF) cavity filter that overcomes the above identified problems. SUMMARY

One of the objects of the present disclosure is to solve or at least minimize the problems mentioned above. This is achieved by the tunable radio freguency (RF) cavity filter as defined in the claims.

In embodiments, there is provided a radio freguency (RF) cavity filter comprising a housing enclosing at least one radio freguency (RF) cavity resonator. Each radio frequency (RF) cavity resonator comprises: a cavity body having a cavity body axis and an inner wall around a cavity hole, wherein the cavity body is arranged so that its inner wall is accessible from the outside of the housing; a dielectric socket comprising a lining member, wherein the lining member is arranged within the cavity body so that it lines at least a part of the inner wall of the cavity body and is exchangeable from the outside of the housing; and a tuning element, arranged within the dielectric socket so that galvanic insulation between the inner wall and the tuning element is obtained and generation of passive inter-modulation is reduced. The tuning element is arranged to be accessible from the outside of the housing so that its position along the cavity body axis can be adjusted, whereby the radio frequency (RF) cavity filter is tuned to frequencies dependent on the position of the tuning element along the cavity body axis. Embodiments of the present disclosure may have at least the advantage of reducing PI in a tunable radio frequency (RF) cavity filter.

In one or more embodiments, the housing comprises a chassis and a chassis lid.

In one or more embodiments, the lining member is plastically deformable and arranged to plastically deform when receiving the tuning element, such that threads in the lining member are formed when the tuning element changes position along the cavity body axis in response to a rotational movement of the tuning element.

An advantage of embodiments of the present disclosure may be that production time is significantly reduced by eliminating the need to thread a large number of holes in the chassis or the chassis lid, this also reduces the percentage of throw-away components such as the chassis or chassis lid. Yet an advantage is to reduce the risk for increased PIM during the lifespan of the filter, especially when retuning the filter, as the risk of further metal flakes or shavings being released from the threads and falling into the filter is eliminated. Yet another advantage of the present disclosure is that the dielectric socket, or at least the lining member, can easily be replaced, e.g. if the threads are damaged. Yet an advantage is that production time is reduced as the time consuming production step of reworking is eliminated, i.e. the need to open the filter again, clean the components inside, close the filter and retune the filter again.

In one or more embodiments, the inner wall of the cavity body is at least partly conical. This makes it easier to exchange the dielectric socket from the outside of the housing. In one or more embodiments, the lining member is also at least partly conical. This makes it even easier to exchange the dielectric socket from the outside of the housing, since the dielectric socket may then not be held in place by any friction when the tuning element is removed and thus may fall out automatically when the housing is turned.

In one or more embodiments, the lining member is continuous and lines the entire inner wall of the cavity body. Alternatively, the lining member contains openings and only lines parts of the inner wall of the cavity body .

In one or more embodiments, the whole dielectric socket is exchangeable from the outside of the housing.

In one or more embodiments, the dielectric socket comprises a rotational lock member which is arranged to inhibit the socket from rotating. The housing may comprise a recess for each cavity body, wherein the recess is arranged to receive the rotational lock member such that rotation of the socket around the cavity body axis is inhibited.

Yet an advantage of embodiments of the present disclosure is that the socket may be designed with a relatively high level of friction between the tuning element and the dielectric socket without risking that the socket starts moving with the tuning element, e.g. in response to rotational movement of the tuning element . In one or more embodiments, the socket may further comprise an axial lock member arranged to inhibit movement of the dielectric socket along the cavity body axis .

Yet an advantage of embodiments of the present disclosure may be that the socket is prevented from falling out of the cavity body when handling the chassis .

In one or more embodiments, the dielectric socket further comprises a friction member which is arranged to control the friction between the tuning element and the dielectric socket.

Yet an advantage is that the time reguired for tuning and thus production time is reduced as the tuning element locking step is eliminated as the disclosure provides for a friction member providing sufficient friction between the tuning element and the socket to withstand vibration and maintain its relative position.

Yet an advantage of the present disclosure is that the PI levels in the radio freguency (RF) cavity filter may be further reduced by introducing PIM improved tunable coupling elements between a cavity body pair.

In one or more embodiments, the housing encloses a plurality of radio freguency (RF) cavity resonators, and comprises at least one coupling element between at least two of the radio freguency (RF) cavity

resonators. At least one of the coupling elements may be a fixed coupling element, e.g. an internal wall within the housing. Alternatively or additionally, at least one of the coupling elements may be a tunable coupling element, which may e.g. be configured to adapt the coupling between pairs of radio freguency (RF) cavity resonators in response to a rotational movement of at least a part of the tunable coupling element.

The scope of the invention is defined by the claims, which are

incorporated into this section by reference. A more complete

understanding of embodiments of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a tunable radio freguency (RF) cavity filter, in accordance with one or more embodiments of the disclosure.

Figs . 2a and 2b both show a cavity body pair in a section of a tunable radio freguency (RF) cavity filter, in accordance with one or more embodiments of the disclosure. Figs. 3a and 3b both show a dielectric socket for a tunable radio freguency (RF) cavity filter 100, in accordance with one or more embodiments of the disclosure.

Fig. 4 shows a chassis further forming a recess and a socket hole, in accordance with one or more embodiments of the disclosure. Fig. 5 shows a cavity body pair and a tunable coupling element, in accordance with one or more embodiments of the disclosure .

Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Introduction

The level of Passive Inter odulation (PI ) is an extremely important characteristic of a cavity filter, and a high level of PIM may be a problem in conventional cavity filters. PIM may be, as previously mentioned, e.g. due to manufacturing defects such as metal flakes or shavings inside the chassis or inconsistent contact between component surfaces, such as between a tuning element and a cavity body. Yet another problem is that the tuning process of adjusting tuning elements reguires both a tuning step and a locking step, e.g. fixating a tuning screw with a tuning screw locking nut. The locking step is reguired as the tuned freguencies of the filter are extremely sensitive to a change in position of the tuning element. This increases the production time, the complexity of the tuning process, the construction of the filter and the level of PI , e.g. as the galvanic contact between locking nut and chassis, or the galvanic contact between tuning screw and chassis, may vary with the tightening torgue of the locking nut. Yet another problem is that conventional filters use threaded holes for receiving tuning element, typically in a chassis lid. Threading the holes is a cumbersome and time consuming production step resulting in a certain percentage of throw-aways or discarded components. For example, if a single one out of a larger number of holes is not threaded correctly, the chassis or chassis lid will have to be discarded.

Yet another problem is that as the tuning element changes position within the cavity body in the tuning process, further metal flakes or shavings may be released from the threads and fall into the filter chassis thus affecting PIM. This might be the case at initial filter production or at a later stage when the filter is retuned.

Yet another problem is that when using conventional tuning elements in the form of screws in threaded holes in the chassis or chassis lid, the production process reguires an additional step of reworking, or more simply opening the filter, cleaning the components inside, closing the filter and retuning the filter. This might sometimes amount to 60% of the production time of a filter.

Fig. 1 shows a tunable radio freguency (RF) cavity filter 100, in accordance with one or more embodiments of the disclosure . In

embodiments, a radio freguency (RF) cavity filter 100 comprises a housing enclosing at least one radio freguency (RF) cavity resonator 120. The housing may comprise a chassis 110 and a chassis lid. In embodiments, the chassis 110 may serve multiple purposes such as acting as an enclosure for the filter protecting against environmental aspects, such as dust, and/or acting as a shield protecting against Electro Magnetic

Interference EMI and/or controlling coupling between cavity resonators within the chassis, e.g. by forming walls 1101 separating pairs of cavity bodies. The chassis may in one example be made from metal. In other examples, the chassis may be made from metalized plastic or any other material suitable for acting as a shield protecting against Electro Magnetic Interference EMI and/or controlling coupling between cavity resonators within the chassis, as would be understood by a skilled person. In one or more embodiments of the present disclosure, the chassis may comprise a chassis bottom. In yet an embodiment of the present disclosure, the chassis may comprise four chassis side walls, e.g. as shown in fig. 1 by the side walls 1102, 1103. In embodiments, the chassis forms 110 a single or a plurality of cavity body/bodies 130. In

embodiments, the chassis forms a cavity body 130 for each radio freguency (RF) cavity resonator 120 enclosed by the housing. In embodiments, each cavity body 130 comprises a cavity body axis 1303. In embodiments, the cavity body 130 is elongated and hollow. In embodiments, the cavity body axis 1303 is the longitudinal axis of the cavity body 130. In

embodiments, the cavity body 130 comprises an outer wall 1302 and an inner wall 1301, around a cavity hole 1107. The cavity body 130 may be arranged so that its inner wall 1301 is accessible from the outside of the housing. In embodiments, the cavity body 130 is attached to or integrated into to the chassis bottom at one end. In embodiments, a cross section, orthogonal to the cavity body axis, of the cavity body 130 may be circular, oval, rectangular or guadratic or any other shape suitable for a cavity body 130. In embodiments, the chassis 110 may be configured to receive a chassis lid (not shown in the figure) to form a housing, wherein the chassis lid may be galvanically coupled or connected to the chassis, e.g. by fastening arrangements such as fastening-screws, rivets, soldering or welding. In embodiments, the chassis lid may comprise an inner chassis lid and an outer chassis lid, wherein the inner lid may be in galvanic contact with the chassis such that the chassis together with the chassis lid provides shielding against Electro Magnetic Interference EMI, and the outer chassis lid may be fastened to the chassis such that it protects against environmental aspects such as dust and/or shielding against Electro Magnetic Interference EMI .

In embodiments, the coupling between radio freguency (RF) cavity

resonators 120 within the chassis is controlled by adapting or

controlling the distance between cavity bodies of the radio freguency (RF) cavity resonators within the chassis. In embodiments, the coupling between radio freguency (RF) cavity resonators 120 within the chassis is controlled by introducing fixed coupling elements 1101, e.g. in the form of internal walls 1101, or tunable coupling elements 160, between cavity bodies of the radio freguency (RF) cavity resonators. In embodiments, the chassis 110 is further configured with at least one input RF connector 1104 and at least one output RF connector 1105, wherein the RF connectors 1104, 1105 are configured to connect the radio freguency (RF) cavity filter to external units to feed an input signal into the filter and provide an output signal from the filter.

Cavity bodies 130 and coupling elements 1101 can mainly be adapted during manufacturing of the filter. However, the radio freguency (RF) cavity resonators 120 and thereby the filter may be tuned by receiving tuning elements 150 into the cavity bodies 130. In conventional filters, the tuning elements are inserted into threaded holes in the inner chassis lid of the filter, and are arranged to change longitudinal position in response to rotational movement. This affects the volume of the cavity body, thereby tuning the radio freguency (RF) cavity resonator to freguencies dependent on the position of the tuning element.

In one or more embodiments, the present disclosure may improve PIM characteristics of the filter by allowing the tuning element 150 to interact directly with the cavity body 130, as opposed to the chassis lid as in conventional filters. In one or more embodiments, the present disclosure therefore further improves PIM characteristics of the filter, by eliminating galvanic contact between the tuning element 150 and the inner wall 1301 of the cavity body 130 formed by the chassis 110 by inserting a dielectric socket 140 comprising a lining member 1402 in each cavity body 130, so that a lining member 1402 lines at least a part of the inner wall 1301 of the cavity body 130 of each of the RF freguency resonators 120, thereby allowing the tuning element 150 to interact directly with the cavity body 130 via the dielectric socket 140. The lining member 1402 may be exchangeable from the outside of the housing.

Fig. 2a shows an embodiment of a RF freguency resonator 120 pair in a section of a tunable radio freguency (RF) cavity filter 100, in

accordance with one or more embodiments of the disclosure . In

embodiments, each radio freguency (RF) cavity resonator 120 comprises a cavity body 130. The cavity body 130 has a cavity body axis 1303, an inner wall 1301, and an outer wall 1302. In embodiments, the cavity body axis 1303 is the central axis of the cavity body 130.

In embodiments, each radio freguency (RF) cavity resonator 120 comprises a dielectric socket 140, comprising a lining member 1402, which is arranged within the cavity body 130 so that it lines the inner wall 1301 of the cavity body 130, such that the inner wall 1301 is galvanically insulated from the tuning element 150, both when the tuning element 150 is stationary and when the tuning element 150 changes position along the cavity body axis 1303 within the cavity body 130 in response to

rotational movement. In embodiments, the dielectric socket 140 is rotationally locked such that rotation of the dielectric socket 140 is inhibited. In some embodiments the dielectric socket 140 is, additionally or alternatively, axially locked such that movement along the cavity body axis is inhibited.

Thus, PI characteristics can be improved, as PI contribution from galvanic contact between each tuning element 150 and the chassis lid is eliminated. Further, as the tuning element 150 interacts directly with the dielectric socket 140 in the cavity body 130, the risk of residue metal flakes or shavings being released from the threads in the chassis lid and falling into the filter chassis 110 is eliminated. In one or more embodiments, a tunable radio frequency (RF) cavity filter 100 comprises a housing enclosing at least one radio frequency (RF) cavity resonator 120. Each radio frequency (RF) cavity resonator 120 comprises a cavity body 130 having a cavity body axis 1303 and an inner wall 1301 around a cavity hole 1107, wherein the cavity body (130) is arranged so that its inner wall (1301) is accessible from the outside of the housing. Each radio frequency (RF) cavity resonator 120 further comprises a dielectric socket 140 comprising a lining member 1402, wherein the lining member 1402 is arranged within the cavity body 130 so that it lines the inner wall 1301 of the cavity body 130 and is

exchangeable from the outside of the housing. Each radio frequency (RF) cavity resonator 120 further comprises a tuning element 150, arranged within the dielectric socket 140 so that galvanic insulation between the inner wall 1301 and the tuning element 150 is obtained and generation of passive inter-modulation is reduced. The tuning element 150 may be arranged to be accessible from the outside of the housing so that its position along the cavity body axis 1303 can be adjusted, whereby the radio frequency (RF) cavity filter 100 is tuned to frequencies dependent on the position of the tuning element 150 along the cavity body axis 1303.

In embodiments, the housing comprises a chassis 110 and a chassis lid.

The tuned frequencies of a radio frequency (RF) cavity filter 100 are extremely sensitive to a change in position of the tuning element. It may therefore be important that the change of position along or parallel to the cavity body axis 1303 within the cavity body 130, e.g. in in response to a longitudinal and/or rotational movement of the tuning element 150, may be precisely controlled and repeatable. In one or more embodiments the present disclosure may solve this by providing a dielectric socket 140 comprising a lining member 1402 which is plastically deformable such that threads in the lining member 1402 are permanently formed when receiving a tuning element 150. The tuning element 150 can then be subjected to rotational movement back and forth and still return to the same position along or parallel to the cavity body axis 1303 within the cavity body 130. In embodiments, the tuning element 150 changes position in response to a longitudinal and/or rotational movement of the tuning element 150. In embodiments, the tuning element 150 may be arranged to change position along or in parallel to the cavity body axis 1303 within the cavity body 130 in response to a longitudinal movement. In

embodiments, the tuning element 150 is arranged to change position along or in parallel to the cavity body axis 1303 within the cavity body 130 in response to a rotational movement. In embodiments, the tuning element 150 may be arranged to change position along or in parallel to the cavity body axis 1303 within the cavity body 130 in response to a longitudinal movement and/or a rotational movement. In one example, the lining member 1402 of the dielectric socket 140 plastically deforms when receiving a tuning screw, such that threads in the lining member 1402 are formed when the tuning screw is turned, or subjected to a rotational movement, and changes position along or parallel to the cavity body axis 1303 within the cavity body 130.

Thus the need for pre-threaded holes for receiving tuning elements 150 may be eliminated, as threads in the socket are formed when the tuning element changes position along or parallel to the cavity body axis 1303 within the cavity body 130. Further, the cumbersome and time consuming production step of threading holes may be eliminated. Further, the percentage of throw-aways or discarded components can be reduced.

Fig. 2b shows another embodiment of a RF freguency resonator 120 pair in a section of a tunable radio freguency (RF) cavity filter 100, in accordance with one or more embodiments of the disclosure. According to this embodiment, the inner wall 1301 of the cavity body 130 is conical instead of cylindrical. This makes it easier to exchange the dielectric socket 140 from the outside of the housing. The lining member 1402 of the dielectric socket 140 may be cylindrical or conical. If the lining member 1402 of the dielectric socket 140 is also conical, this makes it even easier to exchange the dielectric socket 140 from the outside of the housing, since the dielectric socket 140 may then not be held in place by any friction and thus may fall out when the housing is turned and no tuning element 150 is inserted.

Fig. 3a shows a dielectric socket 140 for a tunable radio freguency (RF) cavity filter 100, in accordance with one or more embodiments of the disclosure. In one or more embodiments, when the tuning element 150 changes position along or parallel to the cavity body axis 1303 within the cavity body 130, e.g. in response to rotational movement, there will be friction between the tuning element 150 and the dielectric socket 140. This friction may cause the dielectric socket 140 to change position, e.g. to rotate around the cavity body axis 1303, unless the dielectric socket 140 is rotationally locked. The present disclosure provides a rotational lock by introducing a dielectric socket 140 comprising a rotational lock member 1401 arranged to inhibit the dielectric socket 140 from rotating e.g. around the cavity body axis 1303. In embodiments, there may be provided a dielectric socket 140 that comprises a lining member 1402 arranged for lining at least a part of the inner wall 1301 of the cavity body 130 such that galvanic insulation between the inner wall 1301 and the tuning element 150 is obtained and generation of passive inter-modulation is reduced. In embodiments, there may be provided a dielectric socket 140 comprising a rotational lock member 1401. In one example, the rotational lock member 1401 may be in the shape of a hexagon, as shown in fig. 3. The present disclosure is not limited to the rotational lock member 1401 having a hexagonal shape - it can also be e.g. in the shape of an octagon, an oval, a half circle, a cross, a triangle, a rectangle or any other non-circular shape suitable for inhibiting rotational movement of the socket 140. In embodiments, the lining member 1402 may further be arranged to protrude through a socket hole in the chassis ready to receive a tuning element 150. In

embodiments, it may also be desirable to prevent the dielectric socket 140 from falling out of the cavity body 130 when the chassis 110 is handled. In an optional embodiment, the dielectric socket 140 may further comprise an axial lock member 1403 configured to inhibit movement of the dielectric socket 140 along or parallel to the cavity body axis 130. In embodiments, the axial lock member 1403 is arranged to engage when a tuning element 150 is inserted and to disengage when no tuning element 150 is inserted. In embodiments, the axial lock member 1403 may be arranged such that movement of the dielectric socket 140 along or parallel to the cavity body axis 1303 is inhibited when the tuning element 150 is inserted and such that movement of the socket 140 along or parallel to the cavity body axis 1303 is not inhibited when no tuning element 150 is inserted. In embodiments, the dielectric socket 140 is made from plastic, e.g. Teflon, Perfluoroalkoxy Alkanes or PFA, PolyEther Ether Ketone PEEK or any other suitable dielectric and/or plastically deformable plastic material. In embodiments, there may be provided an optional friction member 1404 arranged to control friction between the tuning element 150 and the dielectric socket 140. In one example, the friction may then be controlled to a suitable threshold such that the position of the tuning element 150 does not change due to mechanical vibrations of the filter, thus eliminating the need for a locking step in the tuning procedure. The friction threshold can suitably be chosen dependent on the use case of the filter, e.g. in a radio mast or in an eguipment room.

In different embodiments, the dielectric socket 140 may comprise an optional rotational lock member 1401 and/or a lining member 1402 and/or an optional axial lock member 1403 and/or an optional friction member 1404 or any combination thereof. Although Fig. 3 shows the socket having a rotational lock member 1401 and a lining member 1402 with an optional axial lock member 1403, the present disclosure is not limited to this particular combination of socket members. The present disclosure provides for a dielectric socket 140 that may comprise a single member 1401-1404 or multiple members in any combination of the rotational lock member 1401, the lining member 1402, the axial lock member 1403 and/or the optional friction member 1404. These members are not necessarily

separated parts, but may comprise a single unit. In an optional

embodiment, the dielectric socket 140 is further arranged with a friction member 1404 configured such that frictional force on longitudinal and/or rotational movement of the tuning element is controlled to exceed a predetermined threshold. In one example, the friction member 1404 may be ribs arranged along the inside of the dielectric socket 140 parallel to the cavity body axis 1303. In yet an example, the friction member 1404 may be a circular inner wall of the socket lining member 1402 having a diameter smaller than the outer diameter of the tuning element 150, thereby providing friction between the tuning element 150 and the dielectric socket 140. In yet an example, the friction member 1404 may be a hexagonal, octagonal or any other non-circular shaped inner wall of the socket lining member 1402 having a diameter smaller than the outer diameter of the tuning element 150, thereby providing friction between the tuning element 150 and the dielectric socket 140.

Fig. 3b shows another embodiment of a dielectric socket 140 for a tunable radio freguency (RF) cavity filter 100, in accordance with one or more embodiments of the disclosure. According to this embodiment, both the inner wall 1301 of the cavity body 130 and the lining member 1402 of the dielectric socket 140 are conical instead of cylindrical. Further, the lining member 1402 of the dielectric socket 140 is not continuous but instead contains openings, so that it is shaped like a mesh. The shown lining member 1402 thus comprises longitudinal bars joined together by supports. This enables the dielectric socket 140 to contain less

material, so that the properties of the radio freguency cavity resonator 120 are less affected by the dielectric socket 140 while galvanic insulation between the inner wall 1301 and the tuning element 150 is still obtained. The lining member 1402 may have many different shapes as long as the distance between the tuning element 150 and the inner wall 1301 of the cavity body is maintained by the lining member 1402. The lining member 1402 may e.g. just comprise longitudinal bars, or more irregular shapes. The shown dielectric socket 140 is also manufactured from two detachable parts which are joined along the length of the dielectric socket 140, but this is just an exemplary embodiment. The embodiments of fig. 2a, 2b, 3a and 3b may be combined in any way conceivable. A cylindrical lining member 1402 may be continuous or contain openings and be manufactured from one part or several detachable parts. The same applies to a conical lining member 1402. All conceivable lining members 1402 may be used together with cylindrical or conical inner walls 1301.

Fig. 4 shows a chassis 110 of the filter further forming a recess 1106 and a socket hole 1107, in accordance with one or more embodiments of the disclosure. In embodiments, the chassis 110 may further form a recess 1106 and a socket hole 1107 centered on the cavity body axis 1303 for each cavity body 130. In embodiments, the recess 1106 may be arranged to receive the rotational lock member 1401 such that rotation of the dielectric socket 140 around the cavity body axis 1303 is inhibited, e.g. by the recess 1106 having a shape corresponding to the shape of the rotational lock member 1401, allowing the rotational lock member 1401 to slide into the recess 1106 with a tight fit, thus inhibiting rotational movement of the dielectric socket 140. In embodiments, the outline shape of the recess 1106 matches or corresponds to the outline shape of the rotational lock member 1401. In other embodiments, the socket hole may be arranged to receive the lining member 1402 when it protrudes through the socket hole 1107.

Fig. 5 shows a cavity body 130 pair and a coupling element 160, in accordance with one or more embodiments of the disclosure . In

embodiments, PIM levels in the radio freguency (RF) cavity filter 100 may be further reduced by introducing PIM improved tunable coupling elements 160 between a pair of cavity resonators 120. In embodiments, the filter 100 may comprise at least one cavity resonator coupling element 1101, 160 arranged between a cavity resonator 120 pair. In embodiments, the coupling element 160 may be tunable. In embodiments, the coupling element 1101 may be fixed, such as an inner wall 1101 of the chassis 110. In embodiments, the coupling element 160 may be configured to adapt the coupling between pairs of cavity resonators 120 in response to a

rotational movement of at least a part of the coupling element 160. In embodiments, the rotational movement may be performed around a coupling element axis 1603 parallel to the cavity body axis 1303. In embodiments, the coupling element comprises a dielectric rod 1601 and an attenuating member 1602, e.g. a strip made from metal or any other material with a dielectric constant ≠1, i.e. not equal to one. In embodiments, the rod may be rotatably attached to the chassis at one end 1604 and rotatably attached to a chassis lid at the opposing end 1605. In embodiments, the dielectric rod 1601 may further be arranged to hold the attenuating member 1602. In embodiments, the attenuating member 1602 may be arranged to be attached to the rod in between the one end and the opposing end. In embodiments, the attenuating member 1602 is arranged to vary the area exposed to the cavity body 130 pair in response to a rotational movement to control or vary the coupling attenuation between cavity body 130 pairs.

The foregoing disclosure is not intended to limit the present invention to the precise forms or particular fields of use disclosed. It is contemplated that various alternate embodiments and/or modifications to the present invention, whether explicitly described or implied herein, are possible in light of the disclosure. Accordingly, the scope of the invention is defined only by the claims.

Claims

1. A radio frequency (RF) cavity filter (100) comprising a housing enclosing at least one radio frequency (RF) cavity resonator (120), wherein each radio frequency (RF) cavity resonator (120)

comprises : a cavity body (130) having a cavity body axis (1303) and an inner wall (1301) around a cavity hole (1107), wherein the cavity body (130) is arranged so that its inner wall (1301) is accessible from the outside of the housing; a dielectric socket (140) comprising a lining member (1402), wherein the lining member (1402) is arranged within the cavity body (130) so that it lines at least a part of the inner wall (1301) of the cavity body (130) and is exchangeable from the outside of the housing; and a tuning element (150), arranged within the dielectric socket (140) so that galvanic insulation between the inner wall (1301) and the tuning element (150) is obtained and generation of passive inter-modulation is reduced, wherein the tuning element (150) is arranged to be accessible from the outside of the housing so that its position along the cavity body axis (1303) can be adjusted, whereby the radio frequency (RF) cavity filter (100) is tuned to frequencies dependent on the position of the tuning element (150) along the cavity body axis (1303) .

2. The filter of claim 1, wherein the housing comprises a chassis (110) and a chassis lid.

3. The filter of claim 1 or 2, wherein the lining member (1402) is plastically deformable and arranged to plastically deform when receiving the tuning element (150), such that threads in the lining member (1402) are formed when the tuning element changes position along the cavity body axis (1303) in response to a rotational movement of the tuning element (150) .

4. The filter of any one of the preceding claims, wherein the inner wall (1301) of the cavity body (130) is at least partly conical.

5. The filter of claim 4, wherein the lining member (1402) is also at least partly conical.

6. The filter of any one of the preceding claims, wherein the lining member (1402) is continuous and lines the entire inner wall (1301) of the cavity body (130) .

7. The filter of any one of claims 1-5, wherein the lining member

(1402) contains openings and only lines parts of the inner wall (1301) of the cavity body (130) .

8. The filter of any one of the preceding claims, wherein the whole dielectric socket (140) is exchangeable from the outside of the housing.

9. The filter of any one of the preceding claims, wherein the dielectric socket (140) comprises a rotational lock member (1401) which is arranged to inhibit the socket from rotating.

10. The filter of claim 9, wherein the housing comprises a recess (1106) for each cavity body (130) which is centered on the cavity body axis (1303) of each cavity body (130), wherein the recess is arranged to receive the rotational lock member (1401) such that rotation of the socket (140) around the cavity body axis (1303) is inhibited.

11. The filter of any one of the preceding claims, wherein the dielectric socket (140) comprises an axial lock member (1403) arranged to inhibit movement of the dielectric socket (140) along the cavity body axis (1303) .

12. The filter of any one of the preceding claims, wherein the dielectric socket (140) comprises a friction member (1404) which is arranged to control friction between the tuning element (150) and the dielectric socket (140).

13. The filter of any one of the preceding claims, wherein the housing encloses a plurality of radio freguency (RF) cavity resonators

(120) .

14. The filter of claim 13, wherein the housing comprises at least one coupling element (1101, 160) between at least two of the radio freguency (RF) cavity resonators (120) .

15. The filter of claim 14, wherein at least one of the coupling elements is a fixed coupling element (1101) .

16. The filter of claim 15, wherein the fixed coupling element is an internal wall (1101) within the housing.

17. The filter of any one of claims 14-16, wherein at least one of the coupling elements is a tunable coupling element (160) .

18. The filter of claim 17, wherein the tunable coupling element

(160) is configured to adapt the coupling between pairs of radio

freguency (RF) cavity resonators (120) in response to a rotational movement of at least a part of the tunable coupling element (160) .