EP2323214A1

EP2323214A1 - Device for filtering radio frequency signals, coaxial air cavity filter, and manufacturing method thereof

Info

Publication number: EP2323214A1
Application number: EP09306099A
Authority: EP
Inventors: Niels Broholm; Anders Larsen
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2009-11-16
Filing date: 2009-11-16
Publication date: 2011-05-18

Abstract

The invention relates to a device (DEV1) for filtering radio frequency signals, wherein the device (DEV1) comprises at least one resonator cavity (RC) for the radio frequency signals with a base plate, (BP1) and at least one inner conductor (IC1) extending upwards from the base plate (BP1), wherein the of least one inner conductor (IC1) is formed from a metal material and the base plate (BP1) is formed frame plastic material, and wherein the at least one inner conductor (IC1) is mounted to the base plate (BP1) by a molding fixation (MF1). The invention further relates to a coaxial air cavity filter and to a method for manufacturing a device for filtering radio frequency signals.

Description

FIELD OF THE INVENTION

The invention relates to a device for filtering radio frequency signals according to the preamble of claim 1, to a coaxial air cavity filter comprising the device, and to a method for manufacturing a device for filtering radio frequency signals according to the preamble of claim 12.

BACKGROUND

A radio frequency spectral range is split into several sub-ranges for different wireless communication technologies such as mobile communication or satellite communication or in several sub-ranges for a same wireless communication technology but for different operators providing the same wireless communication technology.
Coaxial air cavity filters such as passband filters or stopband filters are used for example in radio communication systems to keep radio frequency signals of a radio communication within a specific radio frequency sub-range for avoiding interference and/or noise in neighbouring radio frequency sub-ranges or for keeping the interference and/or the noise below specific thresholds, which may depend on legal requirements or on radio standard specifications. An operation within the specific radio frequency sub-range and thereby a frequency stability must be independent of operating conditions such as low ambient temperatures or low inner working temperatures around for example- 20 degree Celsius, high ambient temperatures around for example + 50 degree Celsius, or high inner working temperatures around for example + 90 degree Celsius due to heat dissipation.
A coaxial air cavity filter can be manufactured for example with a first metal for a housing with a base plate, sidewalls, and a cover plate of one or several resonator cavities. The housing works as an outer conductor for the radio frequency signals. The coaxial air cavity filter may be further manufactured with a second metal usually with a form of one or several cylinders located at central positions of the one or the several resonator cavities. The one or the several cylinders work as an inner conductor for the radio frequency signals. A temperature related frequency drift of a metal-based coaxial air cavity filter is for example 2.5 MHz across a temperature range between 20 degree Celsius and 70 degree Celsius.
The metal-based coaxial air cavity filter is costly in its manufacturing process because of the inner conductors, which are often turned parts from a solid metal rod with a low CTE (CTE = coefficient of thermal expansion). Furthermore, coaxial air cavity filters are usually used for TMAs (TMA = tower mounted amplifier) and the TMAs are installed at a top of a base station antenna mast. Therefore, installers or maintenance personnel have to carry heavy equipment up and down the base station antenna mast, if metal-based coaxial air cavity filters are used.
Weight and costs of a coaxial air cavity filter can be reduced, by using for the housing and the inner conductor instead of the metal a plastic material and with a coating of an electrical conductive material. But plastic-based coaxial air cavity filters have lower frequency stability in comparison to metal-based coaxial air cavity filters in particular in case of high power applications, because a small layer of the coating of the electrical conductive material may not dissipate heat generated inside the housing of the coaxial air cavity filter sufficiently.
The way of filtering radio frequency signals by using coaxial air cavity filters affects characteristics and capabilities of the coaxial air cavity filters and of a method for manufacturing the coaxial air cavity filters.
Therefore, it is an object of the invention to provide an improved device for filtering radio frequency signals, an improved coaxial air cavity filter, and an improved manufacturing method.

SUMMARY

The object is achieved by a device for filtering radio frequency signals, wherein the device comprises at least one resonator cavity for the radio frequency signals with a base plate and at least one inner conductor extending upwards from the base plate, wherein the at least one inner conductor is formed from a metal material, wherein the base plate is formed from a plastic material, and wherein the at least one inner conductor is mounted to the base plate by a moulding fixation. The object is further achieved by a coaxial air cavity filter comprising the device, and by a method for manufacturing the device for filtering the radio frequency signals.
The invention provides a first benefit of reducing a weight of the device in comparison to a fully metal-based device by forming the at least one inner conductor from the metal material such as copper or steel and by forming the base plate of the resonator cavity and preferably in addition sidewalls of the resonator cavity and a top plate of the resonator cavity from the plastic material. The invention provides a second benefit of increasing a frequency stability of the device in comparison to a fully plastic-based device by providing a larger thermal capacity using the metal-based inner conductor. The invention provides a third benefit of not requiring additional mounting material such as screws, glue, or soldering material for mounting the at least one inner conductor to the base plate and thereby reducing manufacturing costs for the device and total weight of the device.
In an embodiment of the invention, at least one part of a side surface of the at least one inner conductor is enclosed by the plastic material or a further molding material.
This offers a benefit of an improved moulding fixation, if for example the device is exposed to vibrations during transport to its installation location or during its operation for example by vibrations due to influence of wind or even due to influence of earthquakes.
In a further embodiment of the invention, at least one lower part of the at least one inner conductor comprises an outer diameter larger or smaller than a diameter of an opening of the base plate for the moulding fixation. This offers a benefit of a further improved moulding fixation, if for example the device is exposed to vibrations during transport to its installation location or during its operation for example by vibrations due to influence of wind or even due to influence of earthquakes.
In an even further embodiment of the invention, the device comprises a cooling unit outside the at least one resonator cavity and the at least one inner conductor is thermally connected to the cooling unit. This provides an advantage of an improved heat dissipation by guiding the heat generated for example during high power applications at the at least one inner conductor to the outside surface of the base plate of the device and by distributing the heat for example across the outside surface of the base plate. Thereby, one or several local heat regions of the device given by one or several inner conductors can be avoided and the device can be cooled for example by ambient air enclosing the device. In addition, a frequency stability of the device can be further improved.
In a further embodiment of the invention, the cooling unit is a heat-conductive paste or a cooling element formed from a thermal conductive solid-state material. This offers for example a possibility of using on the outside surface of the base plate simply a cost-saving thin layer of the heat-conductive paste or for example a more efficient metal-based cooling element with a large surface and preferably a considerably lower material volume than a metal-based base plate.
In a further embodiment of the invention, the at least one inner conductor extends to on outside surface of the base plate. This provides a first benefit of a more robust moulding fixation of the at least one inner conductor at the base plate. A second benefit is related to a possibility to use a lower part of the at least one inner conductor as a thermal bridge for a deflection of heat generated inside the resonator cavity during operation of the device. Thereby, no extra thermal bridge is required.
In preferred embodiments of the invention, the base plate comprises at least one pedestal for the at feast one inner conductor, at least one first characteristic parameter of the at least one pedestal and at least one second characteristic parameter of the at least one inner conductor are adapted to provide a temperature dependent frequency drift of the device below a predefined threshold, and the at least one first characteristic parameter and the at least one second characteristic parameter are either of the following: total or average height, total or average width, geometrical form, material.
The preferred embodiments offer a first advantage of providing a device with a very low coefficient of thermal expansion offering for example a first frequency drift of 0.5 MHz or lower across a temperature range from +20 degree Celsius to +70 degree Celsius and a second frequency drift of 0.5 MHz or lower across a temperature rage from -40 degree Celsius to +20 degree Celsius. The preferred embodiments offer a second advantage of having a sarge degree of freedom for finding a low temperature dependent frequency drift property by varying one or several characteristic parameters of the at least one pedestal and/or the at least one inner conductor. The predefined threshold may depend for example on an ambient temperature range for operating the device, on a size of a frequency gap between two radio frequency sub-ranges, on legal requirements and/or on radio standard specifications.
In further preferred embodiments of the invention, the metal material is either of the following: steel, invar steel, inox steel, iron, or copper. This offers a large flexibility in using different kinds of metals or different kinds of mental compounds preferably with a coefficient of thermal expansion below a further predefined threshold. The further predefined threshold may depend for example on an ambient temperature range for operating the device, on a size of a frequency gap between two adjacent radio frequency sub-ranges, on legal requirements and/or on radio standard specifications. In an even further preferred embodiment of the invention, the at least one inner conductor comprises an end-to-end opening in an axial direction of the at least one inner conductor. This offers a first advantage of reducing material costs for the at least one inner conductor. A reduction of weight of the device is a second advantage. A further advantage is related to a possibility to use a screwing fixation instead of or in addition to the molding fixation.
In a further alternative, the base plate is formed during a mounting step for mounting the at least one inner conductor by injection molding. This provides the advantages of manufacturing the base plate and the molding fixation in one manufacturing step. Thereby, a manufacturing process for the device can be shortened and manufacturing costs can be reduced.
In even further alternatives, the plastic material is a thermosetting material or a thermoplastic material with glass fillers or mineral fillers. This provides a first advantage of increasing a long-term stability of the base plate and thereby increasing the lifetime of the device. This provides a second advantage of increasing a stiffness of the base plate and thereby increasing the frequency stability of the device according to deformations of the base plate. A low thermal coefficient of expansion of the thermosetting material and the thermoplastic material may be a further advantage.
In even further embodiments of the invention, the thermoplastic material is a combination of polycarbonate and acrylonitrile butadiene styrene or the thermosetting material is either of the following: polyester, two component epoxy resin, polyurethane. This offers a large flexibility in using different kinds of thermoplastic or thermosetting materials for the base plate preferably with a low density depending for example on a size of an area of the base plate, on a size of a thickness of the base plate, and/or on a loading by vibration.
In a further preferred embodiment of the invention, the at least one inner conductor is formed by stamping. This provides a first advantage of not requiring to mill a geometrical form of the at least one inner conductor in a more time consuming manufacturing sub-step. This provides a second advantage of having no bits of waste metal from turning or milling operations such as chips, swarf or turnings. In addition, there is no attrition of milling heads or turning tools.
Further advantageous features of the invention are defined and are described in the following detailed description of the invention.

BRIEF DESCRIPTION OF THE FIGURES

The embodiments of the invention will become apparent in the following detailed description and will be illustrated by accompanying figures given by way of non-limiting illustrations.

Figure 1 shows schematically a block diagram of a device according to a first embodiment of the invention.
Figure 2 shows schematically a block diagram of a device according to a second embodiment of the invention.
Figure 3 shows schematically a block diagram of a device according to a third embodiment of the invention.
Figure 4 shows schematically a block diagram of a device according to a fourth embodiment of the invention.
Figure 5 shows schematically a block diagram of a device according to a fifth embodiment of the invention.
Figure 6 shows schematically a block diagram of a device according to a sixth embodiment of the invention.
Figure 7 shows a perspective sectional top view of a coaxial air cavity filter according to the embodiments of the invention.
Figure 8 shows a perspective sectional bottom view of the coaxial air cavity filter according to the fourth and fifth embodiment of the invention.
Figure 9 shows schematically a block diagram of a method for manufacturing a device according to the embodiments of the invention.

DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows schematically in a block diagram and a cross sectional view a device DEV1 according to a first embodiment of the invention.
The device DEV1 may be for example a low-pass filter, a high-pass filter, a band-pass filter, or a band-stop filter for radio frequency signals of a radio access technology such as GSM/GPRS (GUM = Global System for Mobile Communication, GPRS = General Packet Radio Service), UMTS (UMTS = Universal Mobile Telecommunication Systems), or LTE (LTE = Long Term Evolution). The band-stop filter may be a notch filter.
The device DEV1 may be used in 900 MHz or 1800 MHz frequency bands of GSM or may be used for frequency bands of UMTS, WiMAX, and/or LTE. The DEV1 comprises a hollow housing formed by a base plate BP1, a sidewall SW extending upwards from the base plate BP1, and a cover plate CP mounted to an upper end of the sidewall SW.
The hollow housing encloses and defines a coaxial resonator with a resonator cavity RC. In further preferred alternatives, the hollow housing defines one further or several further coaxial resonators and encloses one further or several further adjacent resonator cavities to provide a wide-band radio frequency applicability and/or to achieve a predefined attenuation of the radio frequency signals depending for example on legal requirements or on radio standard specifications.
The sidewall SW may comprise one or more openings to the one further or the several further adjacent resonator cavities (see for example Figure 7). The base plate 8P1 and the sidewall SW may be different individual components of the device DEV1 and may be linked together for example by gluing, soldering, or by using screws. Preferably, the base plate BP1 and the sidewall SW may be a single component of the device DEV1 as indicated in Figure 1.
The base plate BP1 is formed from a plastic material. The plastic material may be a thermoplastic material. The thermoplastic material can be remelted and remoulded. The thermoplastic material may for example PVC (PVC = polyvinyl chloride), PC (PC = polycarbonate), PU (PU = polyurethane), or a composite material of PC and ABS (ABS = acrylonitrile butadiene styrene). In an alternative, the plastic material may be a thermosetting material with an irreversibly hardening. The thermosetting material may be for example polyimide, Bakelite, or a two component epoxy resin. Preferably, the plastic material may comprise glass fillers, mineral fillers, or additives for reducing a CTE of the plastic material and/or for reinforcing mechanical properties of the plastic material, The plastic material may be preferably filled with glass bubbles in an epoxy foam. Preferably, the plastic material may be an injection molded plastic material. The base plate BP1 is covered by an electrical conductive coating ECC such as a copper layer, a silver layer, or a gold layer. This provides a low insertion loss and good performance according to passive inter modulation. Preferably, the sidewall SW is formed from the plastic material as indicated in Figure 1 or from a further plastic material. In an alternative, the sidewall SW may be formed from a first metal material such as aluminium or copper. The first metal material may be covered by the first electrical conductive coating ECC or a further electrical conductive coating. If the sidewall SW is formed from the plastic material or the further plastic material, the sidewall SW is covered by the electrical conductive coating ECC as indicated in Figure 1 or by the further electrical conductive coating. The device DEV1 further comprises an inner conductor IC1 preferably centrally located within the resonator cavity RC and extending upwards from the base plate BP1, In further alternatives, the device DEV1 may comprise one further inner conductor for the further one resonator cavity or several further inner conductors for the several further resonator cavities. The resonator cavity RC may be tuned into a specific resonance frequency by a tuning screw. The tuning screw may be mounted outside the cover plate CP and extends through the cover plate CP into the resonator cavity RC (not shown in Figure 1 for simplification). The specific resonance frequency depends on a penetration depth of the tuning screw into the resonator cavity RC. In an alternative, the tuning screw may extend into the inner conductor IC1.
The inner conductor IC1 is formed from a second metal material such as iron, copper, steel, or stainless/inox steel. The staintess/inox steel may be for example invar steel. The second metal material may be covered by the first electrical conductive coating ECC, the further electrical conductive coating, or an even further electrical conductive coating such as copper, silver, or gold.
The inner conductor IC1 may comprise a hollow body with an opening at a top level IC1_TL of the inner conductor IC1 in an axial direction AD of the inner conductor IC1 as shown in Figure 1, with an end-to-end opening in the axial direction AD from the top level IC1_TL of the inner conductor IC1 to a bottom level IC1_BL of the inner conductor IC1 or comprises a solid body. Preferably, the inner conductor IC1 comprises a cylindrical form. The inner conductor IC1 is mounted to the base plate BP1 by a moulding fixation MF 1.
The moulding fixation MF1 may be provided for example between the bottom level IC1_BL of the inner conductor 1C1 and a top level BP_TL of the base plate BP1 as shown in Figure 1.
Figure 2 shows schematically in a block diagram and a cross sectional view a device DEV2 according to a second embodiment of the invention. The elements in Figure 2 that correspond to elements of Figure 1 have been designated by same reference numerals.
In comparison to Figure 1, an inner conductor IC2 of the device DEV2 comprises a solid body. In an alternative, the inner conductor IC2 may comprise a hollow body as shown in Figure 1.
Further, in comparison to Figure 1, a moulding material MM preferably forms a cover around a lower part of a side surface of the inner conductor IC1 for providing a further moulding fixation MF2 in addition to the moulding fixation MF1. Thereby, a mounting fixation is strengthened and an overall moulding fixation can be improved.
The moulding material MM may be different to the plastic material of the base plate 8P1. Preferably, the moulding material MM and the plastic material of the base plate BP1 may be a same plastic material.
Figure 3 shows schematically in a block diagram and a cross sectional view a device DEV3 according to a third embodiment of the invention. The clements in Figure 3 that correspond to elements of Figure 1 or Figure 2 have been designated by same reference numerals.
A lower part of an inner conductor IC3 comprises an outer diameter OD1 larger than outer diameter of an upper part of the inner conductor IC3. The plastic material of a base plate BP2 comprises an opening for a moulding fixation MF3 for mounting the lower part of the inner conductor IC3. The opening comprises a diameter OD2 at a top level BP2_TL of the base plate BP2 smaller than the outer diameter OD1 of the lower part of the inner conductor IC3 and preferably identical to the outer diameter of the upper part of the inner conductor IC3.
The lower part of the inner conductor IC3 is enclosed by the plastic material of the base plate BP2.
Figure 4 shows schematically in a block diagram and a cross sectional view a device DEV4 according to a fourth embodiment of the invention. The elements in Figure 4 that correspond to elements of Figure 1 to 3 have been designated by same reference numerals.
In comparison to Figure 3, the device DEV4 comprises in addition a thermal bridge TB and a cooling unit CU. In an alternative, the device DEV4 may comprise more than one thermal bridge, if the device DEV4 comprises more than one inner conductor. In a further alternative, the cooling unit CU may be split in two or more sub-units, wherein each sub-unit may be thermally connected to a different thermal bridge. In an even further alternative, the cooling unit CU may be used for two or more adjacent coaxial resonators or even for two or more devices.
The thermal bridge TB may be located between a bottom level IC3_BL of the inner conductor IC3 and a bottom level BP3_BL of the base plate BP3 and thermally connects the inner conductor IC3 and the cooling unit CU. The bottom level BP3_BL is an outside of the base plate BP3.
Therefore, the base plate BP3 comprises an end-to-end opening from the bottom level BP3_BL of the base plate BP3 to the opening for the moulding fixation MF3 or to a bottom level IC3_BL of the inner conductor IC3. A cross section of the end-to-end opening of the base plate BP3 in the axial direction AD of the inner conductor IC3 may be for example circular or quadratic. The thermal bridge TB comprises a thermal conductive material such as aluminium, gold, copper, or silver for deflecting heat generated at conductive materials inside the resonator cavity RC.
The cooling unit CU may be located at the bottom level BP3_BL of the base plate BP3. In an alternative, the cooling unit CU may be located at an outer sidewall of the device DEV4 with a further thermal bridge thermally connecting the thermal bridge TB and the cooling unit CU.
The cooling unit CU may be for example a heat-conductive paste coated at the outside of the base plate BP3. In an alternative, the cooling unit CU may be a cooling element formed from a thermal conductive solid-state material. The cooling element may be for example a metal casing with several cooling fins CF1, CF2, ..., CF12. The metal casing may be formed for example from aluminium or copper.
The cooling unit CU may be mounted to the outside of the base plate BP3 for example by means of screws or bolts, by soldering or brazing, or by using an adhesive.
A thickness T_CU of the metal casing of the cooling unit CU may be preferably a fraction (for example between a third and a fifth or between a fifth and a tenth) of a thickness T_BP of the base plate BP3. Thereby, a total weight of the base plate BP3 formed from the plastic material and of the cooling unit CU may be smaller than a weight of a base plate formed from a metal materials and fulfilling predefined stiffness requirements.
The inner conductor IC3 may be mounted to the base plate BP3 by the moulding fixation MF3. In an alternative, the inner conductor IC3 may be mounted to the base plate BP3 by means of screws or bolts, by soldering or brazing, by using an adhesive, or by means of mating threads provided by the inner conductor IC3 and the base plate BP3. The screws or bolts preferably may be used as a thermal bridge between the bottom level IC3_BL of the inner conductor IC3 and the outside of the base plate BP3 by extending from the bottom level IC3_BL of the inner conductor IC3 to the outside of the base plate BP3. Thereby, an additional thermal bridge is not required.
Figure 5 shows schematically in a block diagram and a cross sectional view a device DEV5 according to a fifth embodiment of the invention. The elements in Figure 5 that correspond to elements of Figure 1 to 4 have been designated by same reference numerals.
In comparison to Figure 4, an inner conductor IC4 of the device DEV5 extends to an outside of a base plate BP4 of the device DEV5. A lower part of the inner conductor IC4 being extended from an inside of the base plate BP4 to an outside surface of the base plate BP4 may be used as a thermal bridge similar to Figure 4. Thereby, an extra thermal bridge is not required. The inner conductor IC4 may be for example a cylindrical tube with an end-to-end opening in the axial direction AD. Preferably, the lower part of the inner conductor IC4 may be expanded from a third outer diameter OD3 at an inside of the base plate BP4 to a fourth outer diameter OD4 at an outside of the base plate BP4.
The inner conductor IC4 may be mounted to the base plate BP4 for example by a moulding fixation MF4. A plastic material of the moulding fixation MF4 preferably encloses the lower part of the inner conductor IC4. In a further preferred alternative, the lower part of the inner conductor IC4 comprises openings for a continuous material connection between the plastic material of a first part of the base plate BP4 inside the lower part of the inner conductor IC4 and the plastic material of a second part of the base plate BP4 outside the lower part of the inner conductor IC4. Thereby, a material stiffness of the base plate BP4 can be improved.
Figure 6 shows schematically in a block diagram and a cross sectional view a device DEV6 according to a sixth embodiment of the invention. The elements in Figure 6 that correspond to elements of Figure 1 to 5 have been designated by same reference numerals.
A base plate BP5 of the device DEV6 comprises at an inside a pedestal PED for an inner conductor IC5 of the device DEV6. In an alternative, the base plate BP5 may comprise at the inside a further pedestal for a further inner conductor or further pedestals for further inner conductors of the device DEV6. The base plate BP5 and the pedestal PED are preferably formed in a single part from a same plastic material. In an alternative, the base plate BP5 is formed from a first plastic material, the pedestal PED is formed from a second plastic material, and the pedestal PED is mounted to the base plate BP5 for example by gluing or injection molding.
A total height H_IC or an average height of the inner conductor IC5 from a top level IC5_TL of the inner conductor IC5 to a bottom level IC5_BL of the inner conductor IC5 at a top level PED_TL of the pedestal PED and a total height H_PED or an average height of the pedestal PED from the top level PED_TL of the pedestal PED to a bottom level PED_BL of the pedestal PED at a top level BP5_TL of the base plate BP5 may be adapted to provide a temperature dependent frequency drift of the device DEV6 below a predefined threshold. The predefined threshold may depend for example on an ambient temperature range for operating the coaxial resonator, on a size of a frequency gap between two radio frequency sub-ranges, on legal requirements and/or on radio standard specifications.
In an alternative, a total width or an average width of the inner conductor IC5 and a total width or an average width of the pedestal PED may be adapted to provide the temperature dependent frequency drift of the device DEV6 below the predefined threshold.
In further alternatives, a geometrical form and/or a material of the inner conductor IC5 and a geometrical form and/or a material of the pedestal PED may be adapted to provide the temperature dependent frequency drift of the device DEV6 below the predefined threshold.
Generally, an amount of extension and contraction of one of the dimensions of the inner conductor IC5 or the pedestal PED depends on a current linear extension of the one of the dimensions of the inner conductor IC5 or the pedestal PED, on a change in temperature ΔT, and on a CTE α of a material of the inner conductor IC5 or the pedestal PED given by a following first equation: $Δ ℓ = (1 + α \cdot ΔT) \cdot ℓ$
A frequency shift ƒ(ΔT) of a resonant frequency ƒ ₀ is given by a following second equation: $f (ΔT) = f_{0} / (1 + α \cdot ΔT)$
The inner conductor IC5 may be for example a cylindrical tube with an end-to-end opening in the axial direction AD. Preferably, a lower part of the inner conductor IC5 may be narrowed from a fifth outer diameter OD5 of an upper part of the inner conductor IC5 at the top level PED_TL of the pedestal PED to a sixth outer diameter OD6 at an intermediate level PED_lL inside the pedestal PED between the top level PED_TL and the bottom level PED_BL of the pedestal PED.
The inner conductor IC5 may be mounted to the base plate BP5 for example by a moulding fixation MF5. A plastic material of the base plate BP5 preferably encloses the lower part of the inner conductor IC5.
Figure 7 shows a perspective sectional top view of a coaxial air cavity filter CACF comprising one or several devices DEV1 to DEV6 according to the embodiments of the invention. The coaxial air cavity filter CACF may be used at a base station such as a base transceiver station, a NodeB, or an enhanced NodeB of a radio communication system such as GSM/GPRS, UMTS, or LATE.
A TMA or a TMB (TMB = tower mounted booster) preferably mounted at a top part of an antenna mast of the base station may comprise one or several of the coaxial air cavity filters.
The coaxial air cavity filter CACF may be a triplexer with three filtering paths: one path for transmission and two paths for reception.
In further alternatives, the coaxial air cavity filter CACF may be a duplexer or a diplexer for a single reception path and a single transmission path.
The coaxial air cavity filter CACF shown in Figure 7 implements exemplarily a first triplexer filter functionality T1 and a second triplexer filter functionality T2. For the sake of simplification, only the first triplexer filter functionality T1 will be explained in more detail.
The first triplexer filter functionality T1 comprises a first signal reception path filter RF1, a second signal reception path filter RF2, and a transmission path filter TF.
A base plate BP of the coaxial air cavity filter CACF is formed from the plastic material.
Resonator cavities of coupled coaxial resonators CR1_6_RF1 of the first signal reception path filter RF1, of coupled coaxial resonators CR1_5_RF2 of the second signal reception path filter RF2, and of coupled coaxial resonators CR1_5_TF of the transmission path filter TF are provided by the base plate BP, by the sidewall SW, and by the cover plate (not shown in Figure 7). Inner conductors of the coupled coaxial resonators CR1_6_RF1, CR1_5_RF2, CR1_5_TF are formed from the metal material and are preferably mounted to the base plate BP by moulding fixations.
In further alternatives, the inner conductors of the coupled coaxial resonators CR1_6_RF1, CR1_5_RF2, CR1_5_TF are mounted to the base plate BP by means of screws or bolts, by soldering or brazing, by using an adhesive, or by means of mating threads provided by the inner conductors of the coupled coaxial resonators CR1_6_RF1, CR1_5_RF2, CR1_5_TF and the base plate BP.
The first triplexer filter functionality T1 comprises two common coaxial resonators CCR1, CCR2 for the signal reception path filters RF1, RF2 and the transmission path filter TF and the resonator cavities of the coupled coaxial resonators CR1_6_RF1, CR1_5_RF2, CR1_5_TF are aligned in a zig-zag-pattern in order to save space.
The base plate BP may comprise two coupling openings CO1, CO2 for coupling a filter functionality to RF and DC electronic circuitry (RF = radio frequency, DC = direct current) being located at an outside of the base plate BP. In an alternative, the base plate BP may comprise the cooling unit at the outside of the base plate BP as shown in Figure 8.
Figure 8 shows a perspective sectional bottom view of the coaxial air cavity filter CACF according to the fourth and fifth embodiment of the invention. The coaxial air cavity filter CACF comprises the cooling unit CU at the outside of the base plate BP. Exemplarily, the cooling unit CU is shown as a metal casing with cooling fins CF1_N. The cooling unit CU is thermally connected to the inner conductors of the coupled coaxial resonators CR1_6_RF1, CR1_5_RF2, CR1_5_TF by thermal bridges such as shown in Figure 4 or Figure 5.
The cooling unit CU may be mounted to the outside of the base plate BP for example by means of screws or bolts, by soldering or brazing, or by using an adhesive.
Different features of the invention such as moulding fixation, cooling unit, base plate comprising pedestal being described by the embodiments according to the Figures 1 to 6 may be used as independent features or as a combination of features even if not described in particular.
Referring to Figure 9, a block diagram of a method MET1 is shown for manufacturing the device DEV1, ..., DEV6 according to the embodiments of the invention.
The sequence and the number of the steps for performing the method MET1 is not critical, and as can be understood by those skilled in the art, that the sequence and the number of the steps may vary without departing from the scope of the invention, e.g. some of the steps may be performed simultaneously or some of the steps are ignored as indicated by dotted arrows in Figure 9.
The manufacturing method MET1 may be performed by a single manufacturer of the device DEV1, ..., DEV6 or one or more steps of the manufacturing method MET1 for manufacturing one or more single components of the device DEV1, ..., DEV6 such as the inner conductor IG1, ..., IC5 and/or the base plate BP1, ..., BP5 may be performed by one or more sub-suppliers and remaining steps may be performed by a manufacturer finishing the device DEV1, ..., DEV6.
In a first step M1, one or more inner conductors IC1, ..., IC5 of the device DEV1,..., DEV6 are formed from the metal material. The one or more inner conductors IC1, ..., IC5 may be formed for example by milling a solid metal block, by costing with a metal liquid, or by stamping a solid metal block or metal disc.
In a further optional step M2, the base plate BP1, ..., BP5 of the device DEV1, ..., DEV6 is formed from the plastic material for example by injection moulding. In an alternative, the sidewall of the device DEV1, ..., DEV6 may be formed in addition to the base plate BP, BP1, ..., BP5 from the plastic material by the further optional step M2.
In a next optional step M3, the base plate BP1, ..., BP5 of the device DEV1, ..., DEV6 is coated with the electrical conductive coating ECC. In an alternative, the sidewall SW of the device DEV1, ..., DEV6 is coated in addition with the electrical conductive coating ECC by the optional step M3. A next step M4 is performed after the first step M1, after the step M2, or after the step M3. In the next step M4, the one or more inner conductors IC1, ..., IC5 are arranged for example in an injection molding machine for a next mounting step M5. In an alternative, the one or more inner conductors IC1, ..., IC5 may be arranged in a gluing machine for the next mounting step M5.
In the next mounting step M5, the one or more inner conductors IC1, ..., IC5 are mounted to the base plate BP1, .., BP5 preferably by a moulding fixation MF1, ..., MF5. The base plate BP1, ..., BP5 may be formed during the step M4 preferably by injection molding.
In further alternatives, the one or more inner conductors IC3, IC4, IC5 are mounted to the base plate BP3, BP4, BP5 by means of screws or bolts, by soldering or brazing, by using an adhesive, or by means of mating threads provided by the one or more inner conductors IC3, IC4, IC5 and the base plate BP3, BP4, BP5.
In a next optional step M6, the base plate BP1, ..., BP5 of the device DEV1, ..., DEV6 may be coated with the electrical conductive coating ECC, if the step M3 has been not performed. In an alternative, the sidewall SW of the device DEV1, ..., DEV6 may be coated in addition with the electrical conductive coating ECC by the optional step M6.
In a further optional step M7, the cooling unit CU may be mounted at the device DEV1, ..., DEV6 preferably at the outside of the base plate BP1, ..., BP5. During the step M7, a thermal bridge TB is provided between the one or more inner conductors IC1, ..., IC5 and the cooling unit CU.
In a next step M8 after the step M5 or after the step M7, further components such as the cover plate CP, tuning screws etc. are mounted at the device DEV1, ..., DEV6.
The method MET1 may be used for manufacturing the coaxial air cavity filter CACF comprising one or several of the devices DEV1, ..., DEV6.

Claims

A device (DEV1, ..., DEV6) for filtering radio frequency signals, said device (DEV1, ..., DEV6) comprising at least one resonator cavity (RC) for said radio frequency signals with a base plate (BP, BP1, ..., BP5) and at least one inner conductor (IC1, ..., IC5) extending upwards from said base plate (BP, BP1, ..., BP5), said at least one inner conductor (IC1, ..., IC5) being formed from a metal material, wherein said base plate (BP, BP1, ..., BP5) being formed from a plastic material and said at least one inner conductor (IC1, ..., IC5) being mounted to said base plate (BP, BP1, ..., BP5) by a molding fixation (MF1, ..., MF5).
Device (DEV2, ..., DEV6) according to claim 1, wherein at least one part of a side surface of said at least one inner conductor (IC2, IC3, IC4, IC5) being enclosed by said plastic material or a further molding material (MM).
Device (DEV3, ..., DEV6) according to claim 2, wherein at least one lower part of said at least one inner conductor (IC2, IC3, IC4, IC5) comprises an outer diameter (OD1, OD4, OD6) larger or smaller than a diameter (OD2, OD3,OD5) of an opening of said base plate (BP2, ..., BP5) for said molding fixation (MF3, MF4, MF5).
Device (DEV4, DEV5) according to any of the preceding claim, wherein said device (DEV4, DEV5) further comprising a cooling unit (CU) outside said at least one resonator cavity (RC) and wherein said at least one inner conductor (IC3, IC4) being thermally connected to said cooling unit (CU).
Device (DEV4, DEV5) according to claim 4, wherein said cooling unit (CU) being a heat-conductive paste or a cooling element formed from a thermal conductive solid-state material.
Device (DEV5) according to any of the preceding claims, wherein said at least one inner conductor (IC4) extends to an outside surface of said base plate (BP4).
Device (DEV6) according to any of the preceding claims, wherein said base plate (BP5) further comprising at least one pedestal (PED) for said at least one inner conductor (IC5), wherein at least one first characteristic parameter of said at least one pedestal (PED) and at least one second characteristic parameter of said at least one inner conductor (IC5) being adopted to provide a temperature dependent frequency drift of said device (DEV6) below a predefined threshold, and wherein said at least one first characteristic parameter and said at least one second characteristic parameter being either of the following: total or average height, total or average width, geometrical form, material.
Device (DEV5, DEV6) according to any of the preceding claims, wherein said at least one inner conductor (IC4, IC5) comprises an end-to-end opening in an axial direction (AD) of said at least one inner conductor (IC4, IC5).
Device (DEV1, ..., DEV6) according to any of the preceding claims, wherein said plastic material being a thermosetting material or a thermoplastic material with glass fillers or mineral fillers.
Device (DEV1, ..., DEV6) according to claim 9, wherein said thermoplastic material being a combination of polycarbonate and acrylonitrile butadiene styrene or said thermosetting material being either of the following: polyester, two component epoxy resin, polyurethane.
A coaxial air cavity filter (CACF) comprising at least one device (DEV1, ..., DEV6) according to any of the preceding claims.
A method (MET1) for manufacturing a device (DEV6, ..., DEV6) for filtering radio frequency signals, wherein said method (MET1) comprising the step of mounting (M5) by a molding fixation (MF1, ..., MF5) at least one inner conductor (IC1, ..., IC5) formed from a metal material to a base plate (BP1,..., BP5) formed from a plastic material, by said at least one inner conductor (IC1 , ..., IC5) extending upwards from said base plate (BP1, ..., BP5) for providing at least one resonator cavity (RC) for said radio frequency signals.
Method (MET1) according to claim 12, wherein said base plate (BP1, ..., BP5) being formed during said mounting step (M5) by injection moulding.
Method (MET1) according to claim 12 or claim 13, wherein said at least one inner conductor (IC1, ..., IC5) being formed by stamping.
Method (MET1) according to claim 12, claim 13, or claim 14, wherein a coaxial air cavity filter (CACF) being manufactured by said method (MET1).