EP2443694B1 - Cavity filter - Google Patents

Description

The invention relates to a cavity filter according to the preamble of claim 1.

In radio systems, especially in the mobile sector, a common antenna is often used for transmit and receive signals. The transmit or receive signals each use different frequency ranges, and the antenna must be capable of transmitting and receiving in both frequency ranges. For the separation of the transmit and receive signals, therefore, a suitable frequency filtering is required, with the one hand, the transmission signals from the transmitter to the antenna and on the other hand, the received signals are forwarded from the antenna to the receiver. For the distribution of the transmission and reception signals, inter alia high-frequency filters in coaxial design are used today.

Coaxial-type high-frequency cavity filters include coaxial resonators in which resonator cavities are formed in an outer conductor housing in which inner conductors are arranged in the form of inner conductor tubes. The inner conductor tubes each have a free end which lies adjacent to a housing cover, which is arranged on the upper side of the housing.

A high-frequency filter is for example from the WO 2006/063640 A1 known. The generic high-frequency filter may consist of a plurality of resonators, each comprising an outer conductor housing, a housing bottom and a preferably arranged coaxially to the outer conductor inner conductor which terminates usually at a distance below the housing cover can be placed on the housing.

As is known, such high-frequency filters, which are also referred to below as HF filters, are made of a metal housing, usually an aluminum housing, for example designed as a milling or casting part, so that no intermodulation problems occur due to joints in the filter. In addition, the housing lid is also typically made of a metal, i. made of a milling or cast part, for example made of aluminum, wherein the housing cover to achieve a good electrical contact with the housing is also preferably silvered.

The housing cover is provided at its peripheral edge with a series of holes which are aligned with corresponding threaded holes in the housing walls of the cavity filter, so that by screwing the housing cover can be firmly attached to the actual housing to thereby to ensure a high-frequency-tight mounting of the lid.

A generic high-frequency filter is for example from the US 3,955,161 A known. It describes a housing construction with a plurality of high-frequency chambers with therein rising from the ground towards the lid inner conductors. Both the high frequency filter housing and the high frequency filter housing closing high frequency filter cover are made of plastic. Both consist of a plastic casting. All surfaces of the HF housing and the HF lid are covered with an electrically conductive layer inside and outside.

In the high-frequency cover itself sitting in corresponding holes screws that can be screwed in different degrees, the screw shafts are aligned with the arranged in the high-frequency filter inner conductors axially. By turning on or unscrewing the screws, the effective distance between the leading end side of the screw shank and the opposite end face of the inner conductor can thus be increased or decreased, whereby a corresponding high-frequency filter can be tuned in a known manner.

A high frequency filter is basically also from the US 5,329,687 A known. This HF filter also comprises an HF housing and an HF cover, which in turn consist of a cast dielectric material, which was then coated with an electrically conductive layer. Also in this case, tuning screws are used, which can be turned on and turned off different distances through corresponding holes in the RF cover while further or less immersed in a corresponding axial recess in an underlying inner conductor of the RF housing. Also by this In turn, the HF filter can be tuned in a known manner.

Furthermore, from the DE 10 2006 030 634 A1 Known as an oscillator arrangement known to have, which has an integrated circuit and an external frequency-determining resonator, wherein the frequency-determining resonator is arranged as a cavity resonator and serves in addition to its electrical function as a housing and carrier for the integrated circuit of the high-frequency oscillator.

From the US 2002/145490 A1 is also known to remove a cavity filter, which comprises a box-shaped housing with side walls and a bottom, the overhead opening is closed by a plate-shaped lid. Within the housing separated by partitions of each individual cavity resonators are provided. The cavity resonators are said to be made by extrusion or molding according to this prior art publication, wherein one or more walls of the filter assembly are formed from a printed circuit board material. The remaining walls should be made in a conventional manner, without this being further specified.

Finally, a cavity filter assembly is also made of WO 02/06686 A1 known. Described herein is a cavity filter which also has a box-shaped structure with a bottom and sidewalls and a top-mounted lid. A certain choice of material was not proposed in this context for the housing.

This prior publication deals with a specific task, such as the Eindrehverhalten a thread member can be improved as a tuning element of the cavity resonator. For this purpose, a tuning sleeve is used in the lid of the cavity filter, which can be pressed in the lid, soldered or secured in any other way. The tuning sleeve has two mutually offset internal thread areas in the axial direction, which do not match exactly with the external thread of the eindrehbaren tuning sleeve herein. Preferably, the threaded sleeve is provided at an axial distance with two radially extending grooves, which allows an axially extending relative position change of the threaded portions to each other, whereby the input and Ausdrehverhalten the tuning member is changed.

In contrast, it is an object of the present invention to provide an improved high-frequency filter, which usually comprises a housing and a housing interior closing lid.

The invention is solved according to the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

Within the scope of the invention it has been found that e.g. despite a silvering of an aluminum cover of an RF filter, a not yet optimally optimal, uniformly reproducible mechanical and above all electrical connection between the cover and the housing can be realized.

Thus, the cavity filters known in the prior art continue to exhibit certain intermodulation problems.

In the context of the invention has now been found that a significant improvement, especially in terms of electrical properties with simultaneous cost reduction can be achieved if it is assumed as in the prior art of a cavity filter housing comprising a cover of a printed circuit board material.

In this case, the printed circuit board material is provided with an electrically conductive layer, preferably a copper layer. The Leiterplatinendeckel is like conventional cover also preferably fixed by screws to the housing walls of the cavity filter by screws and electrically-galvanically connected to the housing, which is why the electrically conductive layer preferably in the form of a copper layer plus a possible additional layer as finishing such. B. silver, gold or tin comes to rest with the housing inner side of the cavity filter.

Due to the use of a printed circuit board as a lid results in a material-related relatively soft conductive layer on the printed circuit board, preferably in the form of the mentioned copper layer, being secured by screwing the lid with a corresponding torque on the filter housing a 100% RF-dense connection for the first time can. Above all, this results in a further cost savings, since not a plastic molded separately lid has to be made and used, but that very inexpensive commercially available on the market circuit boards are used directly as a lid.

In addition, the use of printed circuit board material as a lid also allows the possibility of SMT assembly of the board by means of SMT components (according to the Surface Mounted Technology) and with tuning elements, etc. perform. In the prior art, these tuning elements were pressed into the aluminum lid. According to the invention, a sleeve member provided with an internal thread can be inserted into the printed circuit board in a corresponding bore and, for example, with a circumferential flange on the inside of the HF filter to the electrically conductive layer adjacent (namely soldered) inserted, in which one with an external thread Providing tuning element is far different screwed into the cavity filter to tune the filter accordingly or to set a corresponding resonant frequency. In this case, since the tuning jack, which is inserted in a bore of the printed circuit board is soldered to the formed on the printed circuit board electrically conductive layer, thereby intermodulation problems are avoided.

Because in the prior art only screws are used here, which can be screwed directly into corresponding holes in the coated with an electrically conductive layer plastic plate, with the result that here never ensured a clear electrical-galvanic contact between the screw and the electrically conductive layer can be. This leads to significant deterioration in the handling and practice of a so constructed RF filter.

Finally, proves to be a further advantage in the context of the invention that the printed circuit board material provided in the current process, for example, with a structuring is. In this case, the structuring can be designed in such a way that, for example, direct current lines (DC lines), electronics that can be equipped with the printed circuit board, RF coupling, etc. can be realized.

It is also essential within the scope of the invention that the electrically conductive ground area which completely closes off the coaxial resonator (blocking pot / cup circle) on the upper side of the housing is a fundamental component of the cavity filter.

Figur 1 :

eine Querschnittsdarstellung durch ein Hohlraumfilter mit mehreren, nebeneinander angeordneten (verkoppelten) Resonatoren mit aufgesetztem Deckel;

Figur 2 :

eine Draufsicht auf das Ausführungsbeispiel gemäß Figur 1;

Figur 3 :

eine Querschnittsdarstellung durch das Ausführungsbeispiel gemäß Figur 1 bzw. Figur 2;

Figur 4 :

eine vergrößerte Detaildarstellung des in Figur 1 gezeigten Ausschnittes X, welches das Abstimmelement betrifft; und

Figur 5 :

eine vergrößerte Detaildarstellung des Ausschnittes Y in Figur 3 zur Verdeutlichung der Verschraubung des Deckels mit dem Gehäuse des Hohlraumfilters.

The invention will be described in more detail with reference to drawings. In detail:

FIG. 1:

a cross-sectional view through a cavity filter with a plurality of juxtaposed (coupled) resonators with attached lid;

FIG. 2:

a plan view of the embodiment according to FIG. 1 ;

FIG. 3:

a cross-sectional view through the embodiment according to FIG. 1 respectively. FIG. 2 ;

FIG. 4:

an enlarged detail of the in FIG. 1 shown section X, which relates to the tuning element; and

FIG. 5:

an enlarged detail of the section Y in FIG. 3 to clarify the screwing of the lid with the housing of the cavity filter.

The invention for a cavity filter will be described below with reference to an embodiment, which may for example also be designed as a duplexer, as a bandpass filter or as a band rejection filter, etc.

According to the exemplary embodiment shown, the high-frequency cavity filter 1, which is also sometimes referred to below as an RF cavity filter 1, comprises a housing 3 with a bottom 5 and a plurality of internal conductors 7 extending vertically from the bottom over a partial height of the housing 3.

As a result, an overall filter is ultimately created, which is composed of a plurality of individual RF cavity filters 1 ".

The in the Figures 1 and 2 (There partially with the cover omitted) shown individual RF cavity filter are each divided into chambers 101 which are separated by boundary walls 105 of a next adjacent single RF cavity filter 101, wherein the boundary walls 105 each consist of two of the side wall portions 6 inwardly projecting wall sections 105 'are formed. As a result, virtually apertures or windows are formed between the wall sections which project only in part inwardly, the individual HF filters 1 "being coupled to one another via these apertures or windows 107 (FIG. FIG. 3 ).

The cavity filter has, for example, an input terminal in the form of a coupling region 9 and a Output terminal in the form of a Auskoppelbereiches 11, which comprises a coupling disc 9 '(capacitive coupling) or a coil or a wire (in the case of inductive coupling) or may comprise, wherein the relevant coupling disk or the relevant coupling coil or the relevant Einkoppeldraht inside with the reference numerals 9 'and 11' for feeding or decoupling an electromagnetic wave are designated. Conventional coaxial connectors with corresponding cable connections can be connected to the input or output connection.

The thus constructed housing 3 with the housing bottom 5 and the inner conductor 7 is formed from a milling or casting, namely of metal or of a metal alloy. Preferably aluminum is used for this purpose. Since the inner conductor is connected to the housing bottom integrally or screwed, thereby intermodulation problems are avoided.

On the circumferential, facing away from the bottom 5 edge 15 ( FIG. 3 ) of the housing 3, a housing cover 17 is placed and screwed with a plurality of screws 19 with the housing 3 fixed.

In order to shield the individual RF cavity filters 1, ie the interior 1 'of the RF cavity filters 1 HF-moderately close to the outside, the housing cover 17 consists of a printed circuit board 21, that is generally made of a plate material 121, which compared to the used Metal for the housing, to the bottom and to the inner conductor circumferentially arranged housing walls 6 at least slightly nachgebbar and / or at least slightly deformable is. As a result, the copper layer 25 provided on the plate material 121 is softer, more flexible and / or more elastic, that is easier to deform, compared with the conventional housing cover 17 made of metal. In addition, the thickness of the printed circuit board 21 or the plate material 121 may be significantly smaller than the thickness of the wall or the bottom or the inner conductor of the RF cavity filter. For example, the thickness of the printed circuit board, as usual, less than 5 mm, in particular less than 4 mm, less than 3 mm and less than 2 mm, for example, by 1 mm (and below) amount. Usually, the minimum thickness will be 1.0 mm, 0.8 mm, 0.5 mm, 0.1 mm or slightly above. As in the detail cross-sectional view according to FIG. 4 can be seen, the total thickness of the printed circuit board and a still discussed below conductive mass layer 25, for example, by 1.5 mm. This thickness D is for example in FIG. 4 located.

Favorable values for the electrically conductive layer of the printed circuit board, preferably in the form of copper, can be around 30 μm to 40 μm, for example around 35 μm. In general, the thickness of the electrically conductive layer can be, for example, 1 μm to 300 μm, in particular 2 μm to 200 μm, 3 μm to 2 μm or 10 μm to 50 μm, above all, as mentioned, 30 μm to 40 μm. In general, it can then be assumed that the thickness of the copper layer or the electrically conductive layer 25, 26 has, for example, a thickness which is less than 20%, in particular less than 10%, 8%, 6%, 4%, 2%, 1% or even less than 0.5% or 0.1% of the thickness of the associated printed circuit board 21. On the other hand, the thickness can also be chosen be that the copper layer is more than 0.1%, in particular more than 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or more than 15% of the thickness of the printed circuit board 21. In other words, thickness ranges of 1% to 5% of the thickness of the printed circuit board 21 are particularly favorable.

On the side facing the housing 3, ie on the inner side or lower side 21a (ie the inside of the housing) facing the inner space 1 'and the peripheral edge 15 of the housing 3, an electrically conductive layer 25 is preferably in the form of a printed circuit board Copper layer 25 'and optionally an additional layer 26 (see FIGS. 4 and 5 ) is provided as a finishing layer, which optional layer 26 may consist of a noble metal such as silver or gold or tin.

By this arrangement, with a correspondingly applied tightening torque to the screws 19, a mechanically strong and therefore electrically unique and thus reproducible connection between the electrically conductive layer 25 and the peripheral and the cover side facing edge 15 or bearing surface 15 of the housing 3, so ultimately with the housing 3, which is ensured by the relative compliance of the printed circuit board 21, ie the plate material 121, and by the tightening torque of the screws 19, that the electrically conductive layer 25, preferably in the form of the copper layer 25 ', circumferentially a clearly defined secure electrical contact to Material of the housing 3 produces and maintains. As a result, contact-related intermodulation problems are avoided.

As shown in the sectional view and the enlarged detail according to FIGS. 3 and 4 It can also be seen, in the material of the printed circuit board 21 corresponding holes 29 are provided in the axial extension to the central axial axis of the inner conductor 7. In these holes 29 then a tuning socket, so a tuning sleeve 31 may be used, which is electrically conductive on its outer circumference or preferably made of metal and according to the embodiment shown has a circumferential stop ring 33, so that a tuning so formed Sleeve 31 can be inserted from below into the respective bore 29 until the stop ring 33 abuts the electrically conductive layer 25. In this position, the peripheral outer edge 33 'is preferably soldered to the adjacent electrically conductive layer 25, preferably in the form of the copper layer 25', wherein the soldering thus formed, ie the solder ring thus formed by the reference numeral 35 in FIG FIG. 3 respectively. FIG. 4 is marked.

In the so mechanically connected to the circuit board 21 and electrically connected to the electrically conductive layer 25 Abstimmbuchse 31 then a corresponding, provided with an external thread tuning element 37 can be screwed in different degrees, whereby the differently far, protruding into the interior tuning stub 37 'in different distance to the inner conductor, ie to the top 7a ( FIG. 1 ) of the inner conductor 7 can end.

In the illustrated embodiment, the inner conductor is in contrast even with a larger diameter and with an axial, extending from its upper end side down over a partial length inner recess 7b (FIG. FIG. 1 ) Mistake, so that in this case the tuning stub 37 'can possibly also dip into this inner recess 7b in order to achieve a different tuning of the cavity filter. The tuning element 37 with the tuning sleeve 31 and their arrangement in the cover forming the printed circuit board 21 is shown as an enlarged detail X in FIG. 4 played separately.

From the enlarged detailed representation Y according to FIG FIG. 5 Furthermore, it can be seen that on the printed circuit board 21 on the outer circumference offset from each other a plurality of mounting holes 41 are inserted, which are aligned with corresponding holes 43 which are parallel to the axial alignment of the inner conductor and thus perpendicular to the plane of the printed circuit board 21 in the housing wall material. 6 are incorporated. These bores 43 may be provided with a corresponding internal thread suitable for the screws 19 used or otherwise be dimensioned such that corresponding fastening screws 19 can be indented when screwed into the bores 43 in the housing wall material 6 of the housing 3.

Finally, it is mentioned that the electrically conductive layer 25, that is, the ground surface formed, preferably in the form of a copper layer 25 'plus a possibly possible additional layer 26, which serves as a finishing and consists for example of silver, gold or tin, which completely closes the coaxial resonator, that is to say, for example, the blocking pot or the cup circle on the upper side of the housing 3, is a fundamental component of the blocking pot or of the cup circuit, that is to say of the coaxial resonator, or of the cavity filter in general.

Finally, it is also mentioned that electrical functions can be realized, for example, on the top side of the printed circuit board 21, that is to say on the outer or upper side 21b opposite the inner space 1 ', for example direct current lines (DC lines) etc. Likewise, electronic components could be used here be provided on the circuit board, for example, SMT components that are positioned according to the known Surface Mounted Technology in an SMT placement process on the circuit board and electrically contacted. Finally, however, additional devices for achieving or avoiding HF coupling etc. may also be provided.

As a precaution, it is mentioned that under certain circumstances corresponding structures explained above can alternatively or additionally also be provided on the lower or inner side 21a of the ground plane by forming certain conductor tracks to form thinner conductive portions (eg, removed by etching) , If necessary, additional metal surfaces may be formed at these locations on the top or outside 21b of the printed circuit board 21. In addition, metallizations in holes (vias) and outer edges (edge metallization) are possible.

The printed circuit board 21 or the printed circuit board material 121 may consist of all suitable and customary materials, ie dielectric materials. Suitable printed circuit board materials are printed circuit boards, such as those offered under the trade name "FR1", "FR2", "FR3", "FR4" or, for example, "FR5". The abbreviation "FR" is known for flame retardant, so flame-retardant. Thus, such printed circuit board materials may consist of the following materials or comprise these materials, including in any combination namely phenolic resin, paper, epoxy resin, glass fiber, glass fiber fabric, ceramic, PTFE (polytetrafluoroethylene - Teflon).

For a better understanding of the advantages of the invention over the prior art, reference is also made to the tabular overview reproduced below, the so-called. E-modulus and bending strength respectively in N-mm ² for a copper foil, a glass fiber epoxy printed circuit board material and a housing cover according to the prior art from AlMg3 reproduces, for example, with the following, in practice usual mean values, for example, by up to +/- 60%, if necessary, but also at least to +/- 50%, +/- 40%, +/- 20% or at least by up to +/- 10% of the following mean values can deviate upwards or downwards. Modulus flexural strength (N / mm ² ) (N / mm ² ) Cu foil 120000 -280 Glasfaserepoxy 22,000 350-450 AlMg3 70,000 230-290

As is known, the amount of elastic modulus (modulus of elasticity) is greater, the more resistance a material opposes to its deformation. A component made of a material with a high modulus of elasticity (eg steel) is thus stiff, and a component made of a material with a low modulus of elasticity (eg rubber) is yielding.

The actual "softness" of the copper foil (Cu foil) provided in the context of the invention is explained by the fact that, due to the distribution of the different material thicknesses - although the modulus of elasticity of the copper foil is considerably higher than that of the material (AlMg3) - Softness "is achieved as in the prior art.

For example, the thickness of the copper on the glass fiber epoxy circuit board layer is, for example, only 0.35 μm, whereas when using a resonator cover according to the prior art, for example consisting of AlMg3, its total thickness is about 1.5 mm. An additional effect is achieved by the combination of copper and glass fiber epoxy, if the relatively high bending strength (rigidity) of the glass fiber epoxy material, a higher contact pressure of the underlying copper layer is achieved with the filter housing over a pure AlMg3 existing lid.

Claims (10)

1. HF cavity filter with the following features:

   - with a housing (3) with a housing floor (5) and a housing wall (6) which rises from the housing floor (5), and at least one inner conductor (7) which is arranged in the interior (1') of the housing (3),

   - the housing (3) with the housing floor (5) and the housing wall (6) and the inner conductor (7) consist of metal,

   - a housing cover (17) is placed on a surrounding edge (15) of the housing wall (6),

   - the housing cover (17) has multiple fixing holes (41), which align with corresponding holes (43) in the housing wall (6),

   - the housing cover (17) seals the housing (3), in which multiple fixing screws (19), which penetrate fixing holes (41) in the housing cover (17) and are screwed into holes (43) which are axially aligned to it in the housing wall (6) of the housing (3),

   - the housing cover (17) consists of a dielectric board material (121), which under the effect of the fixing screws (19) is at least slightly deformable,

   - in the housing cover (17), at least one additional hole (29) is made, and is penetrated by a tuning element (37), and

   - on the underside (21 a) of the dielectric board material (121) facing the interior (1') of the housing and thus the edge (15) of the housing wall (6) facing away from the housing floor (5), an electrically conductive layer (25, 26) is formed, and rests mechanically firmly on the edge (15) under the effect of the fixing screws (19), and is contacted galvanically with the electrically conductive edge (15) of the housing (3),
   characterised by the following further features:

   - the housing cover (17) consists of a printed circuit board (21),

   - the at least one additional hole (29) is made in the printed circuit board (21), into which a tuning socket (31) is inserted, which on its outer circumference, in sections or preferably surrounding it, includes a stop ring (33), which in the fitted state stops on the electrically conductive layer (25), the tuning socket (31), which consists of electrically conductive material, in particular of metal, or is provided with an electrically conductive surface, being soldered to the electrically conductive layer (25), preferably in the region of the stop ring (33),

   - the tuning element (27) can be twisted into the tuning socket (31) to different distances,

   - on the printed circuit board (21), at least one electrically conductive structure is formed, and

   - the electrically conductive structure includes at least one track and/or at least one SMT component and/or at least one HF overcoupling device.
2. HF cavity filter according to Claim 1, characterised in that the printed circuit board (21) has a thickness of less than 5 mm, in particular less than 4 mm, less than 3 mm and in particular less than 2 mm or about 1 mm.
3. HF cavity filter according to either Claim 1 or Claim 2, characterised in that the thickness of the printed circuit board (21) is greater than 0.1 mm, in particular greater than 0.5 mm, 0.8 mm and in particular greater than 1.0 mm.
4. HF cavity filter according to any one of Claims 1 to 3, characterised in that the electrically conductive layer (25, 26) has a thickness between 1 µm to 300 µm, in particular 2 µm to 200 µm, 3 µm to 2 µm or 10 µm to 50 µm, above all 30 µm to 40 µm.
5. HF cavity filter according to any one of Claims 1 to 4, characterised in that the thickness of the electrically conductive layer (25, 26) is less than 20 %, in particular less than 10 %, 8 %, 6 %, 4 %, 2 %, 1 % or even less than 0.5 % or 0.1 % of the thickness of the associated printed circuit board (21), and/or that the thickness of the electrically conductive layer (25, 26) is more than 0.1 %, in particular more than 0.5 %, 1 %, 2 %, 4 %, 6 %, 8 %, 10 % or more than 15 % of the thickness of the printed circuit board (21).
6. HF cavity filter according to any one of Claims 1 to 5, characterised in that the electrically conductive layer (25, 26) consists of a copper layer (25'), which if required is provided on the contact side with an additional layer (26), which for example includes and consists of one or more of the following materials, namely silver, gold or tin.
7. HF cavity filter according to any one of Claims 1 to 6, characterised in that the at least one structuring device is formed on the outside or top (21 b) of the printed circuit board (21).
8. HF cavity filter according to any one of Claims 1 to 7, characterised in that the at least one structuring device is formed partly or entirely on the inside or underside (21a) facing the interior (1') of the HF cavity filter.
9. HF cavity filter according to any one of Claims 1 to 8, characterised in that the printed circuit board material is composed of one or more of the following materials, namely phenolic resin, paper, epoxy resin, glass fibre, glass fibre fabric, ceramic, PTFE.
10. HF cavity filter according to any one of Claims 1 to 9, characterised in that the high frequency filter comprises the housing (3) with the housing floor (5), with the housing wall (6) and with boundary walls (105) forming chambers (101), and the housing cover (17), the housing (3) consisting of metal or a metal alloy, preferably in the formed of a milled part or casting.

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