Tunable high frequency filter

Abstract

The invention relates to an improved tunable high frequency filter of coaxial construction, characterized, inter alia, by the following features: The high frequency filter comprises an outer conductor housing (24) having an inner conductor (10) and a housing cover (22); the resonator (1) comprises a tuning element (30) arranged opposite the inner conductor (10), which in the housing cover (22) is held position-adjustably in the axial position of the tuning element (30), at least indirectly, and which extends into the internal space of the resonator; the tuning element (30) comprises a dielectric material, or is formed from a dielectric material such that between the outer thread (32) and the inner thread (41), current transitions are avoided.

Claims

1. High-frequency filter of a coaxial construction, the high-frequency filter comprising: at least one resonator having an internal conductor and an external conductor housing; the external conductor housing comprising a housing base, a housing cover spaced apart from the housing base, and a housing wall extending around between the housing base and the housing cover; the internal conductor being galvanically connected to the housing base and extending in an axial direction from the housing base towards the housing cover; the internal conductor ending at a distance from the housing cover and/or being galvanically separated from the housing cover; the resonator comprising a tuning element, which is arranged opposing the internal conductor, and which is movably held in an axial location thereof in the housing cover, at least indirectly, and protrudes into a resonator interior, the tuning element having an external thread; the internal conductor comprising a longitudinal recess, which extends from a face end of the internal conductor opposing the housing cover towards the housing base; the tuning element structured to be introduced into the longitudinal recess of the internal conductor; an internal thread formed in one of (a) the housing cover or (b) in a socket which is provided in the housing cover and also connected in the housing cover; the tuning element having the external thread being rotatably arranged in said internal thread; the tuning element being formed from a dielectric material in such a way that current transitions are prevented between the external thread and the internal thread; the tuning element comprising a central portion, by which the tuning element is movably held, the tuning element further comprising a peripheral wall, the tuning element and the peripheral wall being separated from one another by a recess extending around the central portion, in such a way that a separating space is formed between the central portion and the peripheral wall, the central portion and the peripheral wall being interconnected via a tuning element base; and a face end of the socket opposing the housing base being receivable in the separating space between the central portion and the peripheral wall of the tuning element or dipping into said separating space, in such a way that the peripheral wall is arranged between the socket and the internal conductor in the region of the longitudinal recess thereof; wherein the tuning element further comprises a collar, which extends around the tuning element, is connected to the face end of the peripheral wall opposing the housing cover, and extends radially away from the central portion.

2. High-frequency filter according to claim 1, wherein: the housing cover comprises the socket, which is galvanically connected to the housing cover and which extends towards the housing base.

3. High-frequency filter according to claim 1, wherein: the socket has a distal portion which is disposed at the level of the face end of the internal conductor or dips into the longitudinal recess of the internal conductor; and the tuning element protrudes out of the face end of the socket opposing the housing base and thus dips even further into the longitudinal recess of the internal conductor.

4. High-frequency filter according to claim 1, wherein the peripheral wall of the tuning element comprises a rim edge, in such a way that the peripheral wall above the rim edge has a smaller wall thickness than below the rim edge.

5. High-frequency filter according to claim 1, wherein the ratio between an axial height or length (H) of the socket and a diameter (D) of the socket has a value of ≧1.6, 1.7, 1.8, 1.9, 2.0, 2.25, 2.5, 2.75 and/or 3.0.

6. High-frequency filter according to claim 1, wherein: the housing wall and the internal conductor consist of a first material, which has a first thermal expansion coefficient, or the housing wall consists of a first material, which has a first thermal expansion coefficient, and the internal conductor consists of a second material, which has a second thermal expansion coefficient; the tuning element consists of a third material, which has a third thermal expansion coefficient; and the third thermal expansion coefficient of the third material is greater than the first thermal expansion coefficient of the first material and/or greater than the second thermal expansion coefficient of the second material.

7. High-frequency filter according to claim 6, wherein: in the event of an increase in temperature, the tuning element expands more than the internal conductor and the housing wall in the axial direction of said tuning element, in such a way that a greater proportion of the peripheral wall above the rim edge is arranged between the internal conductor and the socket, providing less dielectric material between the internal conductor and the socket, thus decreasing a head capacitance of the resonator; and in the event of a decrease in temperature, the tuning element contracts more than the internal conductor and the housing wall in the axial direction, in such a way that a smaller proportion of the peripheral wall above the rim edge is arranged between the internal conductor and the socket, providing more dielectric material between the internal conductor and the socket, thus increasing a head capacitance of the resonator.

Description

(1) In the following, the invention is described in greater detail by way of drawings, in which, in detail:

(2) FIG. 1 is a schematic axial cross section through a high-frequency filter according to the invention in accordance with a first embodiment of the present invention; and

(3) FIG. 2 is a schematic axial cross section through the high-frequency filter according to the invention in accordance with a second embodiment of the present invention.

(4) In the following description, like reference numerals denote like components or like features, in such a way that a description made once for one component in reference to one drawing also applies to the remaining drawings, avoiding a repeated description.

(5) FIG. 1 shows a high-frequency filter according to the invention, which comprises a resonator 1. However, the high-frequency filter may also comprise a plurality of resonators 1 coupled together. Each resonator 1 comprises an internal conductor 10 and an external conductor housing, which in turn comprises a housing base 20, a housing cover 22 spaced apart from the housing base 20, and a housing wall 24 extending around between the housing base 20 and the housing cover 22. It can be seen from FIG. 1 that the internal conductor 10 is integrally formed with the housing base 20 and the housing wall 24. The housing cover 22 is positioned on the free ends of the housing wall 24, and can for example be mechanically connected to the end faces of the housing wall by means of screws (not shown). However, it is also possible for the housing cover 22 to be integrally formed with the housing wall. A free end 11 of the internal conductor 10, which forms the end face of the internal conductor 10, is at a predetermined distance from the inner face of the housing cover 22.

(6) It can be seen from FIG. 1 that the internal conductor 10 comprises a longitudinal recess 12, which extends from the face end of the internal conductor 10 opposing the housing cover 22 towards the housing base 20. In the resonators 1 shown in FIGS. 1 and 2, the internal conductors 10 are formed as internal conductor tubes 10 or as internal conductor cylinders 10.

(7) It can be seen from FIGS. 1 and 2 that the high-frequency filter further comprises a socket 40, which in the embodiments shown is configured as a threaded socket 40 having an internal thread 41. The threaded socket 40 is galvanically connected to the housing cover 22. The threaded socket 40 may therefore consist of a metal or may consist of a dielectric material which is coated with a metal layer. The same applies to the housing cover 22, which is either formed from a metal or else coated with metal. The socket 40 may also be integrally formed with the housing cover 22, in such a way that the socket 40 is connected to the housing cover 22 in a material fit. It is further possible for the threaded socket 40 to be connected to the housing cover 22 for example by pressing in. However, the threaded socket 40 may also be galvanically connected to the housing cover 22 by soldering or welding.

(8) The threaded socket 40 dips into the longitudinal recess 12 in the internal conductor 10. However, it is also possible for the threaded socket 40 to end at the level of the face end 11 of the internal conductor 10. It is also possible for the threaded socket 40 to end above the face end 11 of the internal conductor 10. The threaded socket 40 shown in FIGS. 1 and 2 also extends outside the resonator interior, in such a way that the housing wall of the threaded socket 40 extends outwards past the housing cover 22.

(9) The high-frequency filter according to the invention further comprises a tuning element 30, which is movably held in the axial location thereof in the socket 40. For this purpose, the tuning element 30 comprises an external thread 32 on a central portion 31. The external thread 32 is engaged with the internal thread 41 of the threaded socket 40, in such a way that the axial location of the tuning element 30 can be changed by twisting said element. The tuning element 30 further comprises a peripheral wall 33, which is separated from the central potion 31 by a recess 35 extending around the central portion 31. A separating space 35 is thus formed between the central portion 31 and the peripheral wall 33. The central portion 31 is connected to the peripheral wall 33 via a tuning element base 36.

(10) The face end of the threaded socket 40 opposing the housing base 20 is received in the separating space 35 between the central portion 31 and the peripheral wall 33 of the tuning element 30. The peripheral wall 33 is thus arranged between the socket 40 and the wall of the internal conductor tube 10. By screwing the tuning element 30 into and out of the resonator interior, the extent to which the peripheral wall 33 is arranged between the threaded socket 40 and the internal conductor 10 can thus be adjusted, in such a way that the head capacitance of the resonator 1 can thus be adjusted. The tuning element 30 preferably consists of a plastics material, in other words of a dielectric. The more material of the peripheral wall 33 that is arranged between the wall of the threaded socket 40 and the wall of the internal conductor 10, the greater the head capacitance of the resonator 1 becomes. As a result, the head capacitance of the resonator can be increased by screwing the tuning element 30 into the longitudinal recess 12 of the internal conductor 10. As a result screwing the tuning element 30 out of the longitudinal recess 12 in the internal conductor 10, there is less dielectric material between the threaded socket 40 and the internal conductor 10, decreasing the head capacitance of the resonator.

(11) Since the tuning element 30 is formed from a dielectric material or from a dielectric, such as a plastics material, no intermodulation problems occur at the contact point of the external thread 32 with the internal thread 41. Screwing the tuning element 30 into the threaded socket 40 does not result in any metal wear which could lead to intermodulation problems.

(12) Since, in other words, the tuning element 30 may for example consist as a whole of a dielectric material such as plastics material, in other words including the external thread 32, there can be no current transmission to the socket which, along with the associated internal thread 41, consists of an electrically conductive material. So as to prevent current transmission of this type, it is basically sufficient, for example, for the outer surface region of the tuning element 30 to consist of a dielectric material, in such a way that the threads as a whole are formed of a dielectric material, in such a way that no current transmission can take place via the internal thread, formed of metal or coated with a metal layer, of the socket 40. Thus, in this case, the axial core could also consist of metal in a smaller diameter than the external diameter of the tuning element 30, since this metal cannot come into contact with the surface of the internal thread 32 of the threaded socket 40 anywhere. Otherwise, it is noted as a basic principle that ultimately not only the tuning element 30, but also the threaded socket, may thus consist in whole or in part of a dielectric material, since a thread-thread engagement with an external thread 32 of the tuning element 30 and an internal thread 41 of the threaded socket 40, each made of dielectric material, likewise results in no current transmission being able to take place in the region of the thread-thread engagement.

(13) The peripheral wall 33, which is arranged between the internal conductor 10 and the threaded socket 40, is an overvoltage protector for the resonator 1. In the coaxial resonator 1, the maximum field strength occurs at the open end 11 of the internal conductor 10. At high transmission powers, the risk of sparkover from the internal conductor 10 to the threaded socket 40 increases. This risk of sparkover is greatly reduced by the peripheral wall 33 of the tuning element 30.

(14) It can be seen from FIGS. 1 and 2 that the peripheral wall 33 of the tuning element 30 comprises what is known as a rim edge 34. The wall thickness of the peripheral wall 33 is smaller above the rim edge 34 than the wall thickness of the peripheral wall below the rim edge 34. In the embodiments shown, the edge 34 faces the threaded socket 40. However, it is also possible for this edge 34 to face the internal wall of the internal conductor 10.

(15) FIG. 2 shows a high-frequency filter in accordance with the second embodiment of the present invention. The construction of the high-frequency filter shown in FIG. 2 is identical to the high-frequency filter shown in FIG. 1, the sole difference being that the tuning element 30 further comprises a peripheral collar 37 which is connected to the face end of the peripheral wall 33 opposing the housing cover 22 and which extends radially away from the central portion 31. This collar 37 results in a further reduction in the sparkover risk, since the collar 37 is positioned above the free end 11 of the internal conductor 10, in such a way that the collar 37 is arranged between the free end 11 and the internal wall of the housing cover 22. Thus, a sparkover between the internal conductor 10 and the housing cover 22 is also reliably suppressed.

(16) The housing base 20, the housing wall 24 and the internal conductor 10 conventionally consist of a metal, in other words of a first material, which has a first thermal expansion coefficient. It is also possible for the housing wall 24 to consist of a first material, which has a first thermal expansion coefficient, and for the internal conductor 10 to consist of a second material, which has a second thermal expansion coefficient. As stated previously above, the tuning element may for example consist of a plastics material, in other words of a third material, which has a third thermal expansion coefficient. The third thermal expansion coefficient of the plastics material is greater than the first thermal expansion coefficient of the first material and/or greater than the second thermal expansion coefficient of the second material. In the event of a temperature increase, this results in the tuning element 30 expanding more than the internal conductor 10 and the housing wall 24, in such a way that a greater proportion of the peripheral wall 33 above the rim edge 34 is located between the internal conductor 10 and the socket 40. As a result, there is less dielectric material, from which the tuning element 30 is formed, between the internal conductor 10 and the socket 40, thus decreasing the head capacitance of the resonator 1.

(17) In turn, in the event of a decrease in temperature, the tuning element contracts more than the internal conductor 10 and the housing wall 24 in the axial direction, meaning that a smaller proportion of the peripheral wall above the rim edge is located between the internal conductor 10 and the socket 40, and this in turn means that there is more dielectric material between the internal conductor 10 and the socket 40. This increases the head capacitance of the resonator.

(18) In the above-disclosed high-frequency filter, the external conductor housing may for example consist of aluminium, brass, Invar steel, cast aluminium or Arnite plastics material comprising glass fibres. The housing cover 22 may also be formed from the same materials. Likewise, the housing along with the internal conductor, the housing base and the housing cover may consist of a dielectric material, which is coated with an electrically conductive layer. Usually, the electrically conductive layer is applied to the cover on the inner face, in such a way that full-area galvanic contact is ensured at the connection point between the housing cover and the peripheral housing walls of the external conductor housing. This electrically conductive layer may also be provided in the region of the socket 40 and thus also cover the internal thread 41 of the threaded socket 40, in such a way that the internal thread is in turn electrically conductive on the surface thereof. The tuning element may for example be formed from acrylonitrile butadiene styrene (ABS plastics material). The internal conductor may be formed from the same materials as the external conductor housing.

(19) In the embodiment shown, it is shown that the threaded socket 40 may optionally also be attached passing through the housing cover at a different height. It has been found to be advantageous for the height H, in other words the axial length H of the threaded socket 40, to be of a dimension ≧1.5 times the internal diameter D of the threaded socket 40, preferably ≧1.6, 1.7, 1.8, 1.9, 2.0 or even 2.25, 2.5, 2.75, 3.0 and/or more. In general, however, it is sufficient for these values to be no greater than 2.0 or 2.5 or else 3.0. In all these cases, it is ensured that the housing as a whole is optimally shielded from the outside, and no electromagnetic radiation can enter or exit.