WO2017158241A1

WO2017158241A1 - Rf filter

Info

Publication number: WO2017158241A1
Application number: PCT/FI2017/050179
Authority: WO
Inventors: Janne PENTTILÄ; Tero Kämäräinen
Original assignee: Tongyu Technology Oy
Priority date: 2016-03-18
Filing date: 2017-03-17
Publication date: 2017-09-21
Also published as: CN107204503B; CN107204503A; EP3430673A1

Abstract

The invention relates to an RF filter comprising a casing (C), a wall structure (W) between a bottom (B) and cover (T) of which defines inside of it at least one compartment (CPA1-CPA4). The RF filter has compartment-specific resonators (R1-R4), and the RF filter comprises a signal port (SP1) and an RF transmission line (TL) connected to it, the RF transmission line being arranged to transfer an RF signal to the compartments (CPA1-CPA4) of the RF fil-ter. In order to support the RF transmission line, the wall structure (W) of the casing (C) comprises one or more supporting brackets (SU1-SU4, SU11-SU13) which are bent from a wall of the wall structure and to which the transmission line (TL) is fixed by means of an insulating mounting (IS).

Description

RF filter

Background of the invention

[0001] The invention relates to an RF filter.

[0002] RF filters, i.e. radio frequency filters, are used as filtering and matching circuits in connection with RF devices, such as transmitters, receivers or transceivers, in particular in the amplifiers therein, in base stations of mobile phone networks, for example.

[0003] Resonator type filters comprise a casing structure with one or more compartments whose shape is defined by the wall structure of the casing.

[0004] Typically, a compartment of the casing structure may contain an inner conductor, referred to as a resonator or a resonator rod, attached to the bottom of the compartment or cavity, a common structure being a coaxial resonator in which the inner conductor, or the resonator, shares a common axis, i.e. is coaxial, with the surrounding compartment or cavity. A compartment in a metal casing and a metal inner conductor in the casing together form a resonant circuit. In more complex high frequency filters, in particular, the casing structure consists of plural compartments, each compartment having a separate inner conductor, or resonator, whereby a plural number of resonant circuits is formed and, with a suitable intercoupling of these, desired frequency responses, i.e. stopbands and passbands, are obtained.

[0005] In RF filters, inside the casing structure, a transmission line may be used, which brings an RF signal to adjacent compartments of the filter from a signal port or a similar connector mounted at an end of the compartment structure. The transmission line in question needs to be attached to something, and it is known to use a vertical supporting arm fixed to the bottom of the filter casing, and it is additionally known to make use of a projection cast on the wall of the casing structure at its manufacturing stage as a support for the transmission line. The structures in question undoubtedly make it possible to support the transmission line, that is, its mounting, but from the point of view of manufacturing them or assembling the filter, they are laborious.

Brief description of the invention

[0006] An object of the invention is thus to provide an RF filter so as to solve or alleviate the aforementioned problems. [0007] The object of the invention is achieved by an RF filter which is characterised by what is disclosed in the independent claim. Preferred embodiments of the invention are disclosed in the dependent claims.

[0008] The benefit of the invention is the accomplishment of a reliable mounting point or a support point for a transmission line in a manner easy to manufacture.

Brief description of the figures

[0009] The invention will now be described in greater detail in connection with some embodiments, with reference to the accompanying drawings, in which:

[0010] Figure 1 is a top view of an RF filter as seen from the direction of the cover of the casing;

[0011] Figure 2 is a side view of an RF filter as seen from the direction of the frontmost long side of the casing,

[0012] Figure 3 is a front diagonal view of the filter without the cover and frontmost side,

[0013] Figure 4 shows the filter of Figure 3 with the cover and frontmost side,

[0014] Figure 5 shows a separating wall of the casing with a bent supporting bracket.

Detailed description of the invention

[0015] With reference to the figures, an RF filter F is disclosed, which filter F may be used in connection with or coupled to an RF device, such as a transmitter, a receiver, a transceiver or an amplifier. The RF device may be a radio unit in a cellular radio network or a module thereof, for example.

[0016] The filter F has signal ports SP1 , SP2, to which a connection may be made by cables that connect the filter F to an antenna and, for example, a transceiver. The short cables shown in Figure 3 by the signal ports SP1 , SP2 may connect the filter to coaxial connectors mounted on the walls of the outer casing (not shown) surrounding it.

[0017] The filter comprises a casing structure C which has a wall structure W and under it, a bottom B, and on top of it, a cover T. The casing structure C, that is, its wall structure W, bottom B, and cover T, is of conductive metal, such as copper or aluminium coated with, for example, silver or another material that improves conductivity. [0018] The RF filter shown in the figures is a coaxial resonator filter, in other words, it has one or more compartments CPA1 -CPA4 and in them correspondingly compartment-specific inner conductors R1 -R4 or resonators, that is, resonator rods which are rectilinear, that is, coaxial with the direction in which the compartment of the casing C extends, so they extend in the perpendicular direction between the cover and bottom. Each compartment CPA1 - CPA4 of the casing together with its resonator R1 -R4 forms a resonator circuit, and adjacent resonator circuits together form a filter with the desired attenuation graph. The filter may be a bandpass filter, for example. The resonators R1 -R4 are fixed to the bottom B of the casing C with screws.

[0019] The bottom ends of the resonators R1 -R4, i.e. the bottom parts of the resonators in Figure 1 are short-circuited to the bottom B of the of the casing C, the bottom acting at the same time as a common ground for the resonators R1 -R4. In Figure 1 the top parts of the resonators R1 -R4 are so- called free ends, which are galvanically isolated from the casing C, particularly from the cover T of the casing. In a case according to Figure 1 , the length of the resonators is approximately a quarter wavelength.

[0020] The wall structure comprised by the casing C, which is thus between the bottom B and the cover T, comprises sides S1 -S2, ends E1 -E2, and separating walls W1 -W3 between the compartments. So, a four- compartment casing structure has three separating walls W1 , W2, W3 between the compartments CPA1 , CPA2, CPA3, CPA4, the role of the separating walls being to separate the compartments and consequently the resonance circuits from one another by preventing excessive capacitive coupling between the free ends of the resonators R1 -R4. In Figure 2, the frontmost long side S2 of the wall structure W of the casing C is closest to the viewer, so the structures seen behind the side S2 are illustrated by a dotted line.

[0021] The filter comprises a signal port SP1 at an end E1 of the casing, and an RF transmission line TL connected to the signal port in question, the RF transmission line TL being arranged to transfer an RF signal to compartments CPA1 - CPA4 of the RF filter. At a second end E2 of the filter, the filter comprises a second signal port SP2. The signal port SP1 may be connected to an RX/TX device, that is, a transceiver, in particular to the amplifier included therein. The signal port SP2 may be connected to an antenna cable. The other end of the transmission line, that is, the right-hand side end in Figure 3, is connected to the second signal port SP2. [0022] The transmission line TL is supported to the wall structure of the casing C. To support the RF transmission line TL, the wall structure of the casing C comprises a supporting bracket SU1 -SU4 which is bent from a wall of the wall structure W and to which the transmission line TL is fixed by means of an insulating mounting IS1 -IS4. Figure 3 shows supporting brackets SU1 -SU4 bent from a wall, which are for projection branches TL1 -TL4 that branch off from the main line ML of the transmission line TL. In particular, a supporting bracket such as SU1 -SU4 bent from a wall is a supporting bracket for supporting the free end of a projection branch SU1 -SU4 branching off from the main line of the transmission line, because the free end of the projection branch is the most susceptible to vibration, which might result in a change in the frequency response of the filter. In Figure 3, the bent supporting bracket SU4 is for the most part invisible behind the projection branch TL4 of the transmission line TL.

[0023] The supporting brackets SU1 1 -SU13 bent from a wall are for supporting the main line ML of the transmission line TL. The transmission line TL, in particular its main line ML, is fixed to the bent supporting brackets SU1 1 - SU13 in question by means of an insulating mounting IS1 1 -IS13.

[0024] The projection branches TL1 -TL4 that extend closer to the resonators R1 -R4 from the main line ML of the transmission line TL may be considered as coupling projections by means of which the capacitive coupling between the resonators R1 -R4 and the transmission line TL takes place. To enhance and adjust capacitive coupling, the projection branches TL1 -TL4 of the transmission line TL comprise coupling parts CP1 -CP4, which may be, for example, bendable plate surfaces, but other shapes, too, are possible. The intensity of the coupling between the resonators R1 -R4 and the transmission line TL is affected by the size of the coupling parts CP1 -CP4 and their distance from the resonator. The coupling parts CP1 -CP4 are best seen in Figure 3.

[0025] For the coupling between the resonators R1 -R4 and the transmission line TL, in particular the coupling between the coupling branches TL1 -TL4, comprised by the transmission line TL, and the resonators R1 -R4 to remain capacitive, the coupling parts CP1 -CP4 in the coupling branches, that is, projection branches TL1 -TL4, are not in a conducting or galvanic contact to the resonators or the casing C of the filter, that is, its body. [0026] It may be noted that in an embodiment a supporting bracket, such as SU3, bent from a wall is at an edge of the wall, because it is there where it may more easily be formed than more to the middle of the wall.

[0027] For the transmission line TL to set and rest easily at a suitable height, the supporting bracket bent from a wall, such as SU3 in Figures 2, 3, and 5, is so positioned on the wall W3 that it is in the vicinity of the resonator cover B at the top part of the compartment, such as at the top part of the compartment CPA3. In such a case, the supporting bracket, such as SU3, bent from the wall is at the free end, in other words the capacitive end of a resonator, such as R3, located at a distance from the cover B, causing the transmission line TL to be placed in the same area.

[0028] It may be noted that a supporting bracket, such as SU2 bent from the wall, is on the separating wall W1 between the compartments, such as CPA1 , CPA2, of the RF filter. The supporting bracket SU3 bent from the wall is on the separating wall W3 between the compartments CPA3, CPA4 of the RF filter.

[0029] The supporting bracket SU1 1 bent from the wall is on the separating wall W1 between the compartments CPA2, CPA3 of the filter. The supporting bracket SU12 bent from the wall is on the separating wall W2 between the compartments CPA3, CPA4 of the filter. The supporting bracket SU13 bent form a wall is on the separating wall W3 between the compartments CPA3, CPA4 of the filter.

[0030] With reference to the above, in one embodiment the same wall, such as W1 , W3, has at least two bent supporting brackets for the transmission line TL. In one embodiment, the same wall, such as separating wall W1 , W3, has a bent supporting bracket for both the main line ML of the transmission line, and a projection branch, such as TL2, TL3, branching off from the main line. It may be noted that a wall, such as the separating wall W1 , has a bent supporting bracket SU2 for the projection branch TL2 of the transmission line, and a bent supporting bracket SU1 1 for the main line ML of the transmission line TL. Correspondingly, a wall, such as the separating wall W3, has a bent supporting bracket SU3 for the projection branch TL3 of the transmission line, and a bent supporting bracket SU13 for the main line ML of the transmission line TL.

[0031] With reference to Figure 5, it is easiest to bend the supporting brackets, such as SU3, to the separating wall piece before installing the separating wall piece in place between the long sides S1 , S2 of the casing C. A plate piece to become the separating wall W3 has been provided with grooves determined by the width of the supporting bracket SU3, due to which the supporting bracket can be bent. The supporting bracket is bent into a substantially right angle, that is, approximately a 90 degree angle with respect to the plane of the separating wall piece surface. It is advantageous for the surface plane of the supporting bracket SU3 to be parallel to the transmission line TL, in which case fixing by the insulating mounting IS3 will be easiest. The isolating mounting IS1 -IS4, IS1 1 -IS13 may be a plastic screw, for example, for which the supporting bracket has a threaded receptacle THR or a similar counterpart.

[0032] The casing C with its structural elements B, T, W, W1 -W3 is of conductive metal, such as copper or aluminium coated with silver, for example.

[0033] The thickness of the wall is preferably at least 0.5 mm, most preferably at least 1 mm.

[0034] It is apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but may vary within the scope of the claims.

Claims

1. An RF filter comprising a casing (C), a wall structure (W) between a bottom (B) and cover (T) of which defines inside of it at least one compartment (CPA1-CPA4), and the RF filter having compartment-specific resonators (R1-R4), and the RF filter comprising a signal port (SP1) and an RF transmission line (TL) connected to it, the RF transmission line being arranged to transfer an RF signal to the compartments (CPA1-CPA4) of the RF filter, characterised in that, in order to support the RF transmission line, the wall structure (W) of the casing (C) comprises one or more supporting brackets (SU1-SU4, SU11-SU13) which are bent from a wall of the wall structure and to which the transmission line (TL) is fixed by means of an insulating mounting (IS), and wherein the wall thickness is at least 0.5 mm.

2. An RF filter as claimed in claim 1, characterised in that the supporting bracket (SU1-SU4, SU11-SU13) bent from a wall is at an edge of the wall.

3. An RF filter as claimed in claim 1 or 2, characterised in that the supporting bracket (SU1-SU4, SU11-SU13) bent from a wall is so positioned on the wall that it is at the top part of a compartment in the vicinity of the resonator cover.

4. An RF filter as claimed in claim 1,2, or 3, characterised in that the supporting bracket (SU1-SU4, SU11-SU13) bent from a wall is at the free end of a resonator (R1-R4) located at a distance from the cover (T).

5. An RF filter as claimed in any one of the preceding claims, characterised in that the supporting bracket (SU1-SU4, SU11-SU13) bent from a wall is on a separating wall (W1, W2, W3) between the compartments of the RF filter.

6. An RF filter as claimed in any one of the preceding claims, characterised in that the same wall (W1 ) has at least two bent supporting brackets (SU2, SU11 ) for the transmission line (TL).

7. An RF filter as claimed in any one of the preceding claims, characterised in that the supporting bracket (SU1 -SU4) bent from a wall is a supporting bracket for supporting a projection branch (TL1-TL4) branching off from the main line (ML) of the transmission line (TL).

8. An RF filter as claimed in claim 7, characterised in that the supporting bracket (SU1-SU4) bent from a wall is a supporting bracket for sup- porting the free end of the projection branch (TL1-TL4) branching off from the main line (ML) of the transmission line (TL).

9. An RF filter as claimed in any one of the preceding claims 1 - 6, characterised in that the supporting bracket (SU11 -SU13) bent from a wall is a supporting bracket for supporting the main line (ML) of the transmission line (TL).

10. An RF filter as claimed in claim 7 and 9, characterised in that the same wall (W1) has a bent support bracket (SU2, SU11) for both the main line (ML) of the transmission line, and the projection branch (TL2, TL3) branching off from the main line (ML).