Coaxial resonator filter and method for manufacturing the same

Abstract: A coaxial resonator filter (30) comprises a wall construction (50) and a plurality of resonators (11-18) mounted in the shell construction (50) for forming a multi-circuit filter. The filter (30) comprises a connecting portion (19) which combines the resonators (11-18), and said connecting portion (19) and the resonators (11-18) are made in one piece, and the resonators extend as long pin-like projections away from the connecting portion, and said resonators made in one piece are located in different sections (41-48) of the shell construction (31) of the coaxial resonator filter.

Description: The invention relates to a coaxial resonator filter comprising a shell construction and a plurality of resonators mounted in the shell construction for forming a multi-circuit coaxial resonator filter. The invention also relates to a method for manufacturing a coaxial resonator filter, wherein a plurality of resonators are mounted in a shell construction for forming a multi-circuit filter. The invention further relates to a coaxial resonator construction comprising a plurality of pin-like resonators. The invention also relates to a method for manufacturing a coaxial resonator construction comprising a plurality of pin-like resonators. Resonator constructions are used for implementing high-frequency circuits, for instance in base stations of mobile phone networks. Resonators can be used, for example, as interface and filtering circuits in the amplifiers of transmitter and receiver units in base stations. In coaxial resonators the shell envelops a conductor which is positioned in the middle of the shell and which can be called, for example, a resonator or a resonator pin. For instance high-frequency filters, particularly more complicated filters, employ a multi-cavity shell construction and so-called sub-band division. In this case the resonator construction has a multi-cavity shell construction, i.e. it comprises a plurality of resonator cavities, each of which forms a separate resonant circuit with the corresponding resonator pin. In a multi-cavity resonator construction, the resonant circuits are coupled to one another in such a manner that the resonator construction provides the desired frequency response in the frequency band. Each resonant circuit is coupled to the following resonant circuit in the switching diagram of the filter. At present, resonators, or resonator pins, in coaxial resonators are manufactured one at a time by cutting them from a metal bar with a lathe. The resonators are positioned one by one on the bottom of the shell construction and secured thereto by screwing and/or soldering. This is an expensive and time-consuming solution, as the resonators are mounted in the shell one by one. It also takes a long time to tune the filter, since the resonators are not sufficiently similar to each other in their mechanical structure. GB 1,421,311 discloses a strip line resonator filter wherein the resonators are mounted on a planar object as a strip-like branched coating which is extremely thin, only a few dozen microns. GB 1,442,227 discloses a waveguide filter for microwave ovens, wherein the resonators belong to a large machined or cast block wherefrom the resonators extend in several different directions. The resonators are within the same waveguide and not enclosed in separate compartments. The solutions of the above-mentioned references are, however, not suitable for coaxial resonator filters, and they are difficult to manufacture or problematic in other respects. Document WO92/22101 describes a shell of the filter that connects several resonators, i.e inner conductors, in order to form an integral one-piece unit comprising the shell and the resonators. The resonators of the integral unit extend only to one direction. An arrangement according to the above mentioned document makes the thickness of the resonator to be bound to thickness of the very thin shell material sheet. The object of the present invention is to provide a new type of filter, a method for manufacturing it, a resonator, and a method for manufacturing it which avoid the problems associated with the known solutions. The object is achieved with a filter of the invention, which is characterized in that the coaxial resonator filter comprises a connecting portion combining a plurality of resonators, and that said connecting portion and the resonators are made in one piece, forming an integral resonator construction, and that the filter comprises one or more such resonator constructions, and that the resonators extend as long pin-like projections away from the connecting portion, and that said resonators made in one piece are located in different sections of the shell construction of the coaxial resonator filter. The object is achieved with a method of the invention for manufacturing a filter, which is characterized in that the resonators of the filter are made as one or more resonator packages in which the resonators are integral with each other and with a connecting portion combining the resonators, and that the resonators are mounted in sections of the shell construction as one or more such package-like resonator constructions. The object is achieved with a resonator construction of the invention, which is characterized in that the resonator construction comprises a connecting portion combining the pin-like resonators, and that said connecting portion and said resonators extend as long pin-like projections away from said connecting portion. The object is achieved with a method of the invention for manufacturing a resonator construction, which is characterized in that the resonators are formed as one or more integral resonator packages in such a manner that the resonators of a resonator package are parts of an integral object of substantially equal thickness, wherein a connecting portion combines the different resonators, forming an integral resonator construction. The solution of the invention has several advantages. The expensive and time-consuming lathing of the resonator pins can be replaced with more rapid and less expensive techniques, such as punching or injection moulding. The coaxial resonator filters can be assembled more rapidly and reliably, because resonators do not have to be mounted separately, and because comb-shaped sets of resonators are used in the invention. In addition, the filter tuning times are shortened, since the resonators are more similar to each other in their mechanical structure. The advantages are particularly obvious in the preferred embodiments of the invention and other embodiments described in greater detail. In the following, the invention will be described in greater detail with reference to the accompanying drawings, in which Figure 1 shows a coaxial resonator construction, Figure 2 shows a sheet blank, of which a coaxial resonator construction can be formed, Figure 3 shows a coaxial resonator filter, Figure 4 is a top view of a second embodiment of the invention, Figure 5 is a side view of the second embodiment of Figure 4, Figure 6 shows a third embodiment of the invention. Figure 2 shows a steel sheet blank 1 of e.g. 3 mm, from which a coaxial resonator construction 2 according to Figure 1 has been removed by punching, for example. In Figure 2, the resonator construction 2 to be removed from the blank 1 by punching is indicated by a broken line. The resonator construction illustrated in Figure 2 comprises a plurality of resonators 11-18, and a connecting portion 19 integral with the resonators 11-18. The resonators 11-18 extend as long pin-like projections away from the connecting portion 19. The resonator construction 2 is thus made in one piece of a steel sheet 2 or another integral piece 2 which is of a conductive material or coated all over with such a material. The Applicant has found punching from a metal sheet 2 to be a preferred technique, but in another preferred embodiment another technique may be used, e.g. compression moulding of a ceramic material, die casting, or injection moulding. Instead of metal, it is also possible to use, for example, plastic, ceramic or some other machineable material. It is also possible to use several materials in one resonator comb 2, but even then the result is an integral piece of material, comprising resonators 11-18 and a connecting portion 19. In one preferred embodiment, the resonator construction 2 made in one piece comprises one or more groups of resonators, e.g. two groups as shown in the figures. In another preferred embodiment, the resonator groups of the resonator construction 2 extend in substantially opposite directions. In this case, the resonator construction 2 is a planar object. The preferred embodiments simplify the manufacture and take up little space. In a preferred embodiment, the connecting portion 19 and the resonators 11-18 form a comb-shaped resonator construction 2 comprising at least one and preferably at least two sets 2a, 2b of resonator pins, which are preferably planar in such a way that the resonator pins 11-14 are substantially on the same plane with each other, and resonator pins 15-18 are substantially on the same plane with each other, and most preferably in such a way that sets 2a and 2b of resonator pins are both substantially on the same plane. The planar shape of the resonator construction facilitates the manufacture. The connecting portion 19 is preferably on the same plane as the pin-like resonators. The resonators and the connecting portion are also equally thick. All the resonators 11-18 and the connecting portion 19 of the resonator construction are thus preferably planar. However, as an example, the planar sets 2a and 2b are not on the same plane but are superimposed or adjacent, substantially parallel planes, in which case the resonator construction, indicated by number 200, could be e.g. U-shaped as shown in Figures 4 and 5. In this case, the resonator comb is made or bent in such a way that the resonators on both sides are substantially parallel to each other. In this case, the resonator groups extend in substantially the same direction, and the connecting portion 219 of the resonator construction is located between the resonator groups, between the lower parts of the resonators. The shape of the resonator comb 2 or 200 can also be different from what is illustrated in Figures 1 to 5, but the Applicant has found the embodiments shown in the figures to be the most useful. In a preferred embodiment of the invention, at least some of the resonators 11-18 comprise a positioning part 11a-18a for coupling members 20 to be connected to the resonators 11-18 or for other supplementary parts. The coupling members 20 can be seen in Figure 3, which illustrates a coaxial resonator filter 30. The filter 30 comprises a shell construction 31 and a plurality of resonators 11-18 mounted in the shell construction for forming a multi-circuit filter 30. The shell construction 31 comprises sections 41-48 defined by a wall construction 50. The resonators 11-18, made in one piece, are located in different sections 41-48 of the shell construction 31 of the coaxial resonator filter. Said coupling members 20 are provided in areas between certain resonators in such a way that they are attached to one resonator and extend through an opening 51 in the wall construction 50 towards another resonator. The area between resonators 12 and 13, for instance, is provided with two coupling members 20 each of which is attached to one of the resonators 12 and 13 and extends towards the other one of the resonators 13 and 12 through an opening 51 in the wall 50. The members 20 adjust the coupling between the resonators to a suitable level. The filter 30, i.e. in practice the resonator construction 2, comprises a connecting portion 19 combining the resonators. This connecting portion 19 and the resonators 11-18 are made in one piece. The resonators of the filter 30 preferably form a comb-shaped resonator construction 2. The resonator comprises connectors 61-63, of which connector 61 is an interface from the antenna, e.g. the antenna of a base station, connector 62 is an RX interface, from which a signal to the receiver of the base station is received, and connector 63 is a TX interface, to which a signal from the transmitter of the base station is supplied. In addition to a base station of a cellular radio network, the present invention can also be applied to other radio transceivers. According to a preferred embodiment of the invention, the resonator comprises a positioning part 11a-18a for a coupling member 20 at the upper end of the resonator and/or a positioning part 11b/18b for a coupling member 21 at the lower end of the resonator. The coupling member 21 can be, for example, a strip-like conductor, by means of which a direct galvanic connection is provided between certain connectors 61-63 and certain resonators to allow a signal to be transferred. Figure 3 shows by way of example a connection strip 21 from the resonators 13 and 14 to the RX connector 62. The positioning parts 11a-18a and 11b-18b form a kind of cog or a similar construction, which allows the coupling members 20 and 21 to be more easily and reliably mounted in the desired position. In the filter of the invention, the resonators 11-14 and correspondingly 15-18 are preferably substantially on the same plane as the adjacent resonators. In this case, the space utilization, manufacture and assembly of the resonator are optimal. A further object of the invention is a method for manufacturing a filter 30, wherein a plurality of resonators 11-18 are mounted in the shell construction 50 of the filter 30 for forming a multi-circuit filter. It is an essential feature that the resonators 11-18 of the filter are manufactured as one or more resonator packages 2 in which the resonators 11-18 are made in one piece, and that the resonators 11-18 are mounted in the shell construction 50 as one or more such resonator packages 2, which facilitates the manufacture and assembly of the filter 30. Figures 1 to 3 illustrate a duplex filter with eight resonator pins: both the RX filter and the TX filter comprise four resonators 11-14 and 15-18. In a possible embodiment (not shown) the resonator construction 2 may include, for example, two resonator packages 2 according to Figure 1; this makes it possible to implement a duplex filter where both the TX filter and the RX filter comprise eight resonator circuits. The invention further relates to a method for manufacturing a resonator construction 2 comprising a plurality of resonators 11-18. According to this method, the resonators 11-18 are formed as one or more integral resonator packages in such a way that the resonators of one resonator package are made in one piece with a connecting portion combining the different resonators. Resonators of different lengths are used to provide the desired frequency response. In the examples illustrated in the figures, the lengths of the resonators vary by 0.5 to 2 mm. The shortest resonator is resonator 16, which is 3.5 mm shorter than the longest resonator 11. The length of the resonators may vary from 32.5 to 36 mm, for example. According to a preferred embodiment, resonators 11-18 of several different lengths are formed in the same resonator package, and the lengths of the resonators are determined during the manufacture of the resonator package, e.g. in the punching step or injection moulding step. This embodiment facilitates the manufacture. As stated above, according to a preferred embodiment, the resonators 11-18 in the resonator construction or part of them comprise one or more positioning parts 11a-18a or 11b-18b for a coupling member such as 20 or 21. According to the preferred embodiment, the method for manufacturing the resonator construction 2 thus comprises providing, simultaneously with the manufacture of the resonator package 2, one or more resonators 11-18 in the resonator package 2 with positioning parts 11a-18a, 11b-18b for a coupling member such as 20 or 21. This embodiment facilitates the manufacture, since these parts are formed at the same time as the actual resonator construction 2, 11-19 is made by, for example, punching. Figure 6 illustrates a third embodiment of the invention. This is the most simplified embodiment. The filter 300 of Figure 6 has a resonator construction 301 comprising at least two resonators 311 and 318. In accordance with the basic idea, the resonators, such as resonators 311 and 318, are integral, preferably parts of the same pin which is preferably cut with a lathe. In this solution, the resonator construction 301 is preferably a continuous bar-like resonator construction 301, 311, 318, where the resonators 311, 318 are at the different ends of the bar. In practice, Figure 6 shows four resonator constructions 301-304, which together form a larger resonator construction comprising four two-part pins 301-304 with resonators 311-318. This embodiment is also advantageous in view of the manufacture of the resonator construction and the assembly of the filter, since there are at least two resonators in each resonator construction. The resonator construction 2 according to the preferred embodiment shown in Figure 3 is integral and comprises resonators 11-14 for a receiver filter block RX and resonators 15-18 for a transmitter filter block TX. Correspondingly, the resonator construction 301 according to Figure 6 is integral and comprises a resonator 311 for a receiver filter block RX and a resonator 318 for a transmitter filter block TX. This facilitates the manufacture. In a preferred embodiment of the invention, the filter is a filter used in a radio transmitter, radio receiver or radio transceiver, e.g. a base station in a cellular radio network. The invention is thus applied in the field of telecommunications.

Claims: A coaxial resonator filter comprising a shell construction (50) and a plurality of resonators (11-18) mounted in the shell construction (50) for forming a multi-circuit coaxial resonator filter, characterized in that the coaxial resonator filter (30) comprises a connecting portion (19) combining a plurality of resonators (11-18), and that said connecting portion (19) and the resonators (11-18) are made in one piece, forming an integral resonator construction (2) that is a different piece than the shell construction of the filter, and that the coaxial resonator filter comprises one or more such resonator constructions (2), and that the resonators extend as long pin-like projections away from the connecting portion, and that said resonators made in one piece are located in different sections (41-48) of the shell construction (31) of the coaxial resonator filter, and that the integral resonator construction (2) comprises two or more groups of resonators extending in opposite directions. A coaxial resonator filter according to claim 1, characterized in that the resonator construction (2) is planar. A coaxial resonator filter according to claim 1, characterized in that the resonators (11-18) form a comb-shaped resonator construction (2) extending in two opposite directions. A coaxial resonator filter according to claim 1, characterized in that the pin-like resonators (11-18) within a resonator group are on the same plane. A coaxial resonator filter according to claim 1 or 4, characterized in that the connecting portion (19) is on the same plane as the pin-like resonators (11-18). A coaxial resonator filter according to claim 1, characterized in that the resonators (11-18) and the connecting portion (19) are equally thick. A coaxial resonator filter according to claim 1, characterized in that the filter is a filter used in a radio transmitter, radio receiver or radio transceiver, e.g. a base station in a cellular radio network. A coaxial resonator filter according to claim 1, characterized in that the resonator construction (2) made in one piece comprises one or more resonators (11-18) both for the transmitter filter block (TX) and for the receiver filter block (RX). A coaxial resonator filter according to claim 1, characterized in that the resonators (11-18) comprise a positioning part (11a-18a, 11b-18b) for a coupling member (20,21) to be attached to the resonator. A coaxial resonator filter according to claim 9, characterized in that the resonator comprises a positioning part (11a-18a, 11b-18b) at the upper end and/or the lower end of the resonator. A method for manufacturing a coaxial resonator filter, said method comprising forming a resonator construction (2) comprising a plurality of pin-like resonators (11-18), mounting the plurality of resonators (11-18) in a shell construction (50) of a filter (30) to form a multi-circuit filter (30), characterized in that the resonators (11-18) of the filter (30) are made as one or more resonator constructions (2) having resonator groups that are extending in opposite directions, the resonators (11-18) of a resonator construction are integral with each other and integral with a connecting portion (19) combining the resonators with equal thickness, and that the resonators (11-18) are mounted in sections (31) of the shell construction as one or more resonator constructions (2). A method according to elaim 11, characterized in that resonators (11-18) of several different lengths are formed in one resonator construction (2), and that the lengths of the resonators (11-18) are determined during the manufacture of the resonator construction (2), in the same step in which the integral unit formed by the connecting portion and the resonators is produced. A method according to claim 11, characterized in that one or more resonators in the resonator construction (2) are provided, in the same step during the manufacture of the resonator construction (2), with positioning parts (11a-18a, 11b-18b) for a coupling member (20, 21). A method according to claim 11, characterized in that the resonator construction (2) is formed from a metal object, such as a metal sheet (1), by punching. A method according to claim 11, characterized in that the resonator construction (2) is manufactured by making the body of the resonator construction of plastic or other material, and coating the body with a conductive material. A method according to claim 11, characterized in that the resonator construction (2) is made of a ceramic material.

Inventors: KOTANEN ANSSI, TIIHONEN MARKKU, KOTANEN, ANSSI, TIIHONEN, MARKKU
Applicants: REMEC OY
Application year: 1996
Main classification: H01P1
IPC codes: H01P1, H01P11