EP2443694A1

EP2443694A1 - Cavity filter

Info

Publication number: EP2443694A1
Application number: EP10722957A
Authority: EP
Inventors: Thomas Kapfinger
Original assignee: Kathrein Austria GmbH
Current assignee: Kathrein Mobilcom Austria GmbH
Priority date: 2009-06-18
Filing date: 2010-06-03
Publication date: 2012-04-25
Anticipated expiration: 2030-06-03
Also published as: WO2010145758A1; EP2443694B1; DE102009025408B4; US8872605B2; ES2411514T3; DE102009025408A1; US20120105176A1

Abstract

The invention relates to an improved HF cavity filter characterized by the following features: the housing cover (17) is made of a circuit board (21); the at least one additional hole (29) is made in the circuit board (21), in which a tuning bushing soldered at the outer circumference to an electrically conductive layer (25) on the circuit board is inserted; the tuning element (37) can be threaded to a varying depth into the tuning bushing (31); at least one electrically conductive structure is implemented on the circuit board (21); and the dielectric conductive structure comprises at least one conductor and/or at least one SMT component and/or at least one HF overcoupling device.

Description

cavity filter

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 transmitted and received signals, high-frequency filters in a coaxial design are nowadays used inter alia.

Coaxial cavity high-frequency cavity filters comprise coaxial resonators in which an outer conductor housing Resonator cavities are formed 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 has become known, for example, from WO 2006/063640 Al. The generic high-frequency filter can consist of a plurality of resonators which each comprise an outer conductor housing, a housing bottom and a preferably coaxial with the outer conductor arranged inner conductor, which usually ends at a distance below the housing can be placed on the housing - lid.

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 formed as a milling or casting component, so that no intermodulation problems occur due to joints in the filter. In addition, also the housing lid is also usually made of a metal, i. made of a milling or casting, 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 a high-frequency-density assembly to ensure the lid.

A generic high frequency filter has become known, for example, from US 3,955,161 A. It describes a housing construction with several high-frequency chambers with inner conductors rising from the floor towards the cover. 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 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 the screws in and out, 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 has basically also become known from US Pat. No. 5,329,687 A. 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 off at different heights via corresponding holes in the HF cover and thereby further or less far into a speak speaking axial recess in an underlying inner conductor of the RF housing. As a result, in turn, the HF filter can be tuned in a known manner.

Finally, from DE 10 2006 030 634 Al an oscillator arrangement as known, which has an integrated circuit and an external frequency-determining resonator, wherein the frequency-determining resonator is arranged as a cavity resonator and in addition to its electrical function as a housing and support for the integrated Circuit of the high-frequency oscillator is used.

The object of the present invention is to provide an improved high-frequency filter, which conventionally comprises a housing and a cover closing the housing interior.

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 shown that a significant improvement, especially with respect to the 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 fastened 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 said copper layer, wherein by screwing the lid with a corresponding torque on the filter housing a 100% - HF-tight connection are guaranteed for the first time can. Above all, this results in a further cost savings, since it is not necessary to produce and use a lid molded separately from plastic, but printed circuit boards that are available on the market at very low cost are used directly as covers.

In addition, the use of printed circuit board material opens up as a cover also the possibility to perform an SMT assembly of the board by means of SMT components (according to the Surface Mounted Technology) and with tuning elements, etc. 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, it proves to be a further advantage in the context of the invention that the printed circuit board material is provided in the current process, for example with a structuring. The structuring can be designed in this case that thereby, for example, DC lines (DC lines), a mitbeückbare with the circuit board electronics, RF coupling, etc. can be realized.

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

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

Figure 1: a cross-sectional view through a cavity filter with a plurality of juxtaposed (coupled) resonators with attached lid;

FIG. 2 shows a plan view of the exemplary embodiment according to FIG. 1;

Figure 3: a cross-sectional view through the

Embodiment according to Figure 1 and Figure 2;

Figure 4: an enlarged detail of the in

Figure 1 shown detail X, which relates to the tuning element; and

FIG. 5: an enlarged detail of the

Section Y in Figure 3 to illustrate 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 several individual RF cavity filters 1 ".

The individual RF cavity filters shown in FIGS. 1 and 2 (partially there with the lid removed) are each subdivided into chambers 101, which are separated by boundary walls 105 from a next adjacent individual RF cavity filter 101, the boundary walls 105 each extending from two of the side wall portions 6 inwardly projecting wall portions 105 'are formed. As a result, as it were, apertures or windows are formed between the wall sections which project only partially inwards, the individual HF filters 1 "being coupled together via these apertures or windows 107 (FIG. 3).

The cavity filter has, for example, an input connection in the form of a coupling-in region 9 and an output connection in the form of a decoupling region 11, which has a coupling-in disk 9 '(capacitive coupling) or a coil or a wire (in the case of an inductive coupling) comprises or may comprise, wherein the relevant coupling disc or the relevant coupling coil or the relevant coupling wire 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, this intermodulation problems are avoided.

On the encircling, facing away from the bottom 5 edge 15 (Figure 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 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. As a result, the copper layer 25 provided on the plate material 121 is compared is softer, more flexible and / or elastic, that is easier to deform with the conventional made of metal housing cover 17. 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 may, as usual, be 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). Usually, the minimum thickness is added 1.0 mm, 0.8 mm, 0.5 mm, 0.1 mm or slightly above it. As can be seen, for example, in the detailed cross-sectional illustration according to FIG. 4, the total thickness of printed circuit board and of a conductive ground layer 25, which will be discussed below, may be, for example, 1.5 mm. This thickness D is shown for example in FIG.

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 such 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 interior 1 'and the peripheral edge 15 of the

Housing 3 facing inner or bottom 21 a

(ie, the inside of the housing) is provided on the printed circuit board 21, an electrically conductive layer 25 preferably in the form of a copper layer 25 'and optionally an additional layer 26 (see Figures 4 and 5) as a finishing layer, said optional layer 26 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 manufactured, is ensured by the relative compliance of the printed circuit board 21, so 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 safe electrical Contact with the material of the housing 3 produces and maintains. As a result, contact-related intermodulation problems are avoided.

As can also be seen from the sectional representation and the enlarged detail illustration according to FIGS. 3 and 4, are provided in the material of the printed circuit board 21 corresponding holes 29 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 circumferential 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 Figure 3 and Figure 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 (Figure 1) of the inner conductor 7 may end.

In the illustrated embodiment, the inner conductor is in contrast even provided with a larger diameter and with an axial, extending from its upper end down over a partial length inner recess 7b (Figure 1), so that here the tuning stub 37 ', if necessary, to achieve a different vote the cavity film ters can also dip into this inner recess 7b. 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 Figure 4 separately.

From the enlarged detailed representation Y according to FIG. 5, it can also be seen that a multiplicity of fastening bores 41 are introduced on the printed circuit board 21 offset from one another on the outer circumference, which are aligned with corresponding bores 43 which are parallel to the axial orientation of the inner conductor and thus perpendicular to the Level of the printed circuit board 21 are incorporated into the housing wall material 6. These holes 43 may be provided with a corresponding internal thread suitable for the screws 19 used or otherwise be dimensioned so that corresponding fastening screws 19 can notch when screwing into the holes 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, for example, particular on the top of the printed circuit board 21, so on the interior 1 'opposite outer or top 21b electrical functions can be implemented, such as DC lines (DC lines), etc. Similarly, electronic components could be provided on the circuit board, for example SMT components, which are positioned and electrically contacted in accordance with the known surface mounted technology in an SMT assembly process on the printed circuit board. 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 may 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) be formed. 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 (through-holes) 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. such Circuit board materials can therefore consist of the following materials or comprise these materials, including in any combination namely phenol resin, paper, epoxy resin, glass fiber, glass fiber fabric, ceramic, PTFE (polytetrafluoroethylene - Teflon).

For a better understanding of the advantages according to the invention over the prior art, reference is also made to the tabular overview reproduced below, which shows the so-called modulus of elasticity and flexural 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 of AlMg3 reproduces, for example, with the following, in practice usual average values, the problem-free example, up to +/- 60%, if necessary, but also at least to +/- 50%, + / -40%, +/- 20% or at least up to +/- 10% of the following mean values may vary upwards or downwards.

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 results in a higher contact pressure of the underlying copper layer with the filter housing compared to a pure cover made of AlMg3.

Claims

Claims;

1. RF cavity filter having the following features: comprising a housing (3) with a housing bottom (5) and one of the housing bottom (5) elevating

Housing wall (6) and at least one in the interior (I ¹ ) of the housing (3) arranged inside conductor • ter (7), the housing (3) with the housing bottom (5) and the housing wall (6) and the inner conductor (7) are made of metal, on a peripheral edge (15) of the housing wall (6) a housing cover (17) is placed, the housing cover (17) has a plurality of fastening bores (41) , which are aligned with corresponding holes (43) in the housing wall (6), the housing cover (17) closes the housing (3), in which a plurality of fastening screws (19), the mounting holes (41) in the housing - cover

(17) pass through and into axially aligned bores (43) in the housing wall (6) of the housing (3) are screwed, the housing cover (17) consists of a dielectric plate material (121), which under effect the fastening screws (19) is at least slightly deformable, in the housing cover (17) is at least one additional bore (29) is introduced, which of a Tuning element (37) is interspersed, and on the interior (I ¹ ) of the housing and thus the housing (bottom) facing away from edge (15) of the housing wall (6) lying lower side (21a) of the dielectric plate material

(121) is an electrically conductive layer (25,

26) formed under the effect of

Fixing screws (19) mechanically rests firmly on the edge (15) and is electrically contacted with the electrically conductive edge (15) of the housing (3). characterized by the following further features: the housing cover (17) consists of a printed circuit board (21), - at least one additional bore (29) is incorporated in the printed circuit board (21), in which a tuning socket (31) used is, which comprises a sectionally or preferably peripheral stop ring (33) on the outer circumference, which in the mounted state on the electrically conductive

Layer (25) is applied, wherein the consisting of electrically conductive material, in particular made of metal or provided with an electrically conductive surface tuning socket (31) with the electrically conductive layer (25) is preferably soldered in the region of the stop ring (33) the tuning element (27) can be turned in different ways in the tuning socket (31), at least one electrically conductive structure is formed on the printed circuit board (21), and the dielectrically conductive structure comprises at least one printed conductor and / or at least one SMT component and / or at least one RF coupling device.

2. RF cavity filter according to claim I ₁ marked thereby, 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 by about 1 mm ,

3. RF cavity filter according to claim 1 or 2, character- ized 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 is.

4. RF cavity filter according to one of claims 1 to 3, characterized in that the electrically conductive

Layer (25, 26) has a thickness between 1 .mu.m to 300 .mu.m, in particular 2 .mu.m to 200 .mu.m, 3 .mu.m to 2 .mu.m or 10 .mu.m to 50 .mu.m, above all, 30 .mu.m to 40 .mu.m.

5. RF cavity filter according to one of claims 1 to 4, characterized in that the thickness of the electrically conductive layer (25, 26) 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) 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. RF cavity filter according to one of claims 1 to 5, characterized in that the electrically conductive layer (25, 26) consists of a copper layer (25 '), optionally provided with an additional layer (26) on the contact side, which for example comprises and consists of one or more of the following materials, namely silver, gold or tin.

7. RF cavity filter according to one of claims 1 to 6, characterized in that the at least one structural device on the outer or upper side (21b) of the printed circuit board (21) is formed.

8. RF cavity filter according to one of claims 1 to 7, characterized in that the at least one structural device wholly or partially on the interior (I ¹ ) of the RF cavity filter facing the inner or underside (21a) is formed.

9. RF cavity filter according to one of claims 1 to 8, characterized in that the printed circuit board material is assembled from one or more of the following materials, namely phenolic resin, paper, epoxy resin, glass fiber, glass fiber fabric, ceramic, PTFE.

10. RF cavity filter according to one of claims 1 to 9, characterized in that the high-frequency filter a housing (3) with a housing bottom (5), with side wall sections (6) and with boundary walls (105) below

Formation of chambers (101) and a housing cover

(17), wherein the housing (3) made of metal or a

Metal alloy consists, preferably in the form of a milling or casting.