AU4400400A

AU4400400A - High-frequency filter

Info

Publication number: AU4400400A
Application number: AU44004/00A
Authority: AU
Inventors: Heinz Schwarz; Wilhelm Weitzenberger
Original assignee: Kathrein Werke KG
Current assignee: Kathrein SE
Priority date: 1999-04-15
Filing date: 2000-04-13
Publication date: 2000-11-02
Anticipated expiration: 2020-04-13
Also published as: DK1169747T3; CA2370133A1; AU769264B2; EP1169747A1; NZ514485A; KR20010112362A; HK1044633A1; ATE219862T1; BR0009723A; DE19917087C2; JP2002542695A; DE19917087A1; CN1166027C; EP1169747B1; DE50000248D1; CN1347578A; WO2000064001A1

Abstract

The invention relates to an improved high-frequency coaxial-type filter which consists of one or more resonators or coaxial filters and which is characterised by: an electrically conductive external conductor (1); an electrically conductive internal conductor (3); a floor (5) which electrically connects the external and internal conductors (1, 3); a housing cover (25) which is opposite the floor (5) and which covers the high frequency filter; and an adjusting or modulating element (17) which is located in or is plunged into the internal conductor (3) at different relative heights in relation thereto; the adjusting element (7) comprises a plunger or modulating element (17), consisting of dielectric material and the plunger or modulating element (17) is supported at a point which is offset in relation to the housing cover (25).

Description

WO 00/64001 PCT/EPOO/03302 High-frequency filter 5 The invention relates to a high-frequency filter of coaxial design according to the preamble of claim 1. A generic high-frequency filter may comprise one or more individual resonators using coaxial technology. 10 Such coaxially constructed high-frequency filters are generally used in radio systems, for example in the mobile radio sector. They can be used there, for example in base stations for mobile radio, specifically 15 for the selection of defined transmitting and receiving bands. DE 21 36 728 Al discloses a coaxial resonator which comprises a cylindrical housing closed by a base and an 20 internal conductor tube, which is situated coaxially with respect to the external conductor. The cylindrically shaped internal conductor tube accommodates a cylindrical internal conductor section, which slides in the internal conductor tube. By means 25 of displacements of the end section of this internal conductor section with respect to the internal conductor tube, resonant tuning with respect to the respective frequency is carried out. In this case, the internal conductor is formed in the shape of a sleeve 30 closed at the end, which is held and anchored at the upper open end of the external conductor tube, in the area of a cover to be fitted. Furthermore, a further high-frequency filter is also 35 known which, in order to tune the respectively relevant frequency band, uses a screw element, which is arranged on the cover of the individual resonator, whose basic structure is cylindrical, and as a result of being WO 00/64001 PCT/EPOO/03302 2 screwed in and out, penetrates to different depths into the internal conductor of the coaxial individual resonator. This also results, as in DE 21 36 728, in a change in the capacitance of the resonator and, as a 5 result of the capacitance change, a frequency change. Finally, EP 0 068 919 Al basically discloses a high frequency resonator which has an adjustment device running transversely with respect to the resonator 10 longitudinal axis and which can be screwed in and out radially from the outside to a different extent through the wall of the resonator. For this purpose, in the interior, this adjusting device has a pin running transversely with respect to the axial direction of the 15 resonator and made of dielectric material, so that by displacing the adjusting device and by means of radial displacement of the aforementioned pin of dielectric material, a change in the capacitance and frequency can be carried out. 20 However, the previous high-frequency filters in the coaxial design outlined have disadvantages. The disadvantage with the tuning design explained is 25 that components for tuning the resonant frequency impair the homogeneity of the electrically conductive surface in the interior of the filter (for example sliding contacts, solder points, transition regions between various materials, etc.) and, as a result of 30 undefined contacts at the relevant points of contact, a disadvantageous change in the frequency response results (intermodulation). In addition, the tuning device requires an amount of 35 space which cannot be disregarded.

WO 00/64001 PCT/EPOO/03302 -3 As a further disadvantage, it should be noted that a temperature change has an effect on the frequency response. 5 It is an object of the present invention to provide a high-frequency filter of coaxial design which is improved by comparison. According to the invention, the object is achieved in 10 accordance with the features specified in claim 1. Advantageous refinements of the invention are specified in the subclaims. With simple means, the present invention provides a 15 clear improvement with respect to conventional high frequency filters or coaxial filters. By using a dielectric tuning element, which can be adjusted in the axial direction into a different height 20 position, plunging into the internal conductor of the coaxial filter, frequency tuning without difficulty may be performed without there being any possibility of undefined contacts, with the consequence of undesired passive intermodulation, being produced as a result. 25 In a preferred embodiment of the invention, the tuning element, consisting of a dielectric material and plunging into the coaxial internal conductor, is not anchored to the cover of the high-frequency filter 30 device, as in the prior art. The anchoring is preferably carried out in such a way that the resultant capacitance between the open end of the internal conductor and the housing cover decreases if there is an increase in temperature, and therefore results in 35 frequency-based temperature compensation of the filter. In this case, it is preferred for the electrical tuning elements to be supported in the internal conductor, WO 00/64001 PCT/EPOO/03302 -4 preferably in the area of the base of the coaxial filter element, such that they can be adjusted into a different height position, in order to permit the temperature compensation previously mentioned. 5 It has proven to be particularly beneficial here to use a dielectric material which has the lowest possible thermal coefficient of expansion. Use is preferably made of a material which has a negative temperature 10 coefficient of the dielectric constant. The invention will be explained in more detail below using drawings, in which, in detail: 15 Figure 1: shows a schematic axial cross section through a high-frequency filter according to the invention in the form of an individual resonator; and 20 Figure 2: shows a schematic horizontal cross section along the line II-III [sic] in figure 1. Figures 1 and 2 show an axial longitudinal section and, respectively, a cross section and in a schematic 25 reproduction an individual resonator using coaxial technology, which will also be referred to below in short as a coaxial resonator or coaxial filter. This comprises an external conductor 1, an internal 30 conductor 3 which, in the exemplary embodiment shown, is arranged concentrically or coaxially therewith, and a base 5, via which the electrically conductive external conductor 1 and the electrically conductive internal conductor 3 are connected electrically to each 35 other. In the exemplary embodiment, in the base area in the interior of the internal conductor 3 there is provided WO 00/64001 PCT/EPOO/03302 -5 an adjusting element 7 which, in the exemplary embodiment shown, comprises a threaded plate or pot 7'. This threaded plate or threaded pot 7' has on its external circumference an external thread 9, which is 5 engaged with a corresponding internal thread 11 which is provided, at least over an adequate axial length, on the inner side of the internal conductor 3 and/or on the inner side of a recess 13 provided axially thereto in the base 5. In the exemplary embodiment shown, the 10 threaded plate or pot 7' has a rotating or driving attachment 15, in the form of a slot in the exemplary embodiment shown, in order here, for example by means of a screwdriver, to perform rotation of the adjusting element 7 and therefore axial displacement of the same 15 with respect to the internal conductor. On this adjusting element 7, a pin-like plunger or tuning element 17 is arranged to be firmly seated and, in the exemplary embodiment shown, is configured like a 20 pin or cylinder. The length, the diameter, the dielectric constant and the fixing point of the dielectric tuning element or cylinder 17 are chosen in such a way that by means thereof the desired resonant frequency in the desired frequency range can be 25 adjusted. Adjustment and tuning of the frequency are then carried out by rotating the adjustment element 7, as a result of which the adjusting element 7 with the dielectric 30 tuning element 17 can be adjusted in the interior of the internal conductor 3 in a different axial height relative to the internal conductor 3, according to the double arrow representation 21. 35 In the exemplary embodiment shown, it can be seen that the upper end of the internal conductor 3, based on the height of the external conductor 1, comes to rest about 10 to 20% of the axial length of the external conductor WO 00/64001 PCT/EPOO/03302 -6 underneath the upper rim 23 of the external conductor 1 and therefore underneath the electrically conductive cover 25. The dielectric tuning element 17 in this case projects to a small extent beyond the upper rim 27 of 5 the internal conductor 3. By rotating the adjusting element 7 and therefore changing the position of the adjusting element [sic] 17, the capacitance between the open end of the 10 internal conductor and the housing cover, and therefore the resonant frequency, can be changed and adjusted and tuned optimally. As can also be seen from the exemplary embodiment 15 shown, the dielectric tuning element 17 does not itself touch the internal conductor 3. Provided that the fixing of the tuning element is carried out only via the adjusting element 7, via the thread engagement provided there, being carried out in the exemplary 20 embodiment shown in the lower area of the internal conductor 3, preferably even only in the base area or in the adjacent area of the internal conductor 3, no undefined undefined [sic] contacts having a detrimental effect on the capacitance response and therefore the 25 frequency response are created at the points of contact. However, the construction shown has a further substantial advantage, since temperature compensation 30 is possible. To this end, a dielectric tuning element is selected which has a temperature expansion coefficient which is lower than the temperature coefficient of the external 35 and/or internal conductor 1, 3 of the coaxial filter. In the event of an increase in temperature, in this case the internal and external conductors become longer, to be specific to a greater extent than the WO 00/64001 PCT/EPOO/03302 -7 change in length of the dielectric tuning element. In this case, the resulting capacitance between the open end of the internal conductor at [sic] the housing cover decreases during an increase in temperature, 5 since the dielectric tuning element 17 specifically does not expand to the same extent, in the sense of an increase in length, as the internal and/or external conductor, with the result that the reduction in frequency which intrinsically results from the 10 relatively high increase in length of the internal and/or external conductor can be compensated for by the reduction in capacitance which is effected at the same time. This response can entirely consistently be optimized by selecting a suitable dielectric material 15 for the tuning element 17. Particularly suitable for this purpose are dielectric materials consisting of ceramic. In this case, materials which are suitable are those which have a very low thermal coefficient of expansion and also a low temperature coefficient of the 20 relative dielectric constant.

Claims

1. High-frequency filter of coaxial design, 5 comprising one or more resonators, which have the following features - having an electrically conductive external conductor (1) - having an electrically conductive internal 10 conductor (3) - having a base (5) connecting the external and internal conductors (1, 3) electrically, - a housing cover (25) opposite the base (5) and covering the high-frequency filter 15 - and having a plunger or tuning element (17) which changes the resonant frequency and which, based on the internal conductor (3), plunges into the latter or is located in the latter in a different axial or height position, 20 characterized by the following further features - the adjusting element (7) comprises a plunger or tuning element (17) of dielectric material, and - the plunger or tuning element (17) is supported at a support point which is located so as to be 25 offset with respect to the housing cover (25).

2. The high-frequency filter as claimed in claim 1, characterized in that the plunger or tuning element (17) is held and supported on a [lacuna] 30 in the interior of the internal conductor (3) and/or in the area of a recess (13) in the base (5).

3. The high-frequency filter as claimed in claim 1 or 35 2, characterized in that the adjusting element (7) has a threaded plate or pot (7') which is provided with an external thread (9), by means of which the adjusting element (7) is connected to and held by WO 00/64001 PCT/EPOO/03302 -9 an internal thread (11) in the interior of the internal conductor (3) and/or the recess (13) in the base (5). 5

4. The high-frequency filter as claimed in one of claims 1 to 3, characterized in that the electrical plunger or tuning element (17) is arranged on the adjusting element (7) and is fixed to the adjusting element (7) so as to be 10 adjustable with it.

5. The high-frequency filter as claimed in one of claims 1 to 4, characterized in that the dielectric plunger or tuning element (17) 15 projects, at least to a slight extent, beyond the upper rim (27) of the internal conductor (3) or ends underneath the latter.

6. The high-frequency filter as claimed in one of 20 claims 1 to 5, characterized in that the coefficient of thermal expansion of the dielectric plunger or tuning element (17) differs from the coefficient of thermal expansion of the internal or external conductor (3, 1). 25

7. The high-frequency filter as claimed in claim 6, characterized in that the coefficient of thermal expansion of the dielectric plunger or tuning element (17) is lower than the coefficient of 30 thermal expansion of the internal or external conductor (3, 1).

8. The high-frequency filter as claimed in claim 6 or 7, characterized in that the temperature 35 coefficient of the dielectric constant of the plunger or tuning element (17) is negative. WO 00/64001 PCT/EPOO/03302 - 10

9. The high-frequency filter as claimed in one of claims 1 to 8, characterized in that the dielectric plunger or tuning element (17) consists of a ceramic material. 5

10. The high-frequency filter as claimed in one of claims 1 to 9, characterized in that the dielectric plunger or tuning element (17) consists of an aluminum oxide ceramic, in particular an 10 A1 2 0 3 ceramic.

11. The high-frequency filter as claimed in one of claims 2 to 10, characterized in that the threaded plate or pot (7') consists of metal.