GB2279182A

GB2279182A - Microwave ceramic filter

Info

Publication number: GB2279182A
Application number: GB9411596A
Authority: GB
Inventors: Christian Block
Original assignee: Siemens Matsushita Components GmbH and Co KG
Current assignee: TDK Electronics AG
Priority date: 1993-06-09
Filing date: 1994-06-09
Publication date: 1994-12-21
Also published as: KR950002109A; GB9411596D0; GB2279182A8; JPH0722811A

Abstract

A microwave ceramic filter has at least two resonators 11, 12 coupled to one another and arranged interdigitally. A structure 16 for coupling to an external circuit is provided on each resonator. A third resonator 10 may be provided such that the central resonator 12 is rotated by 180 DEG in relation to the outer resonators 10, 11. Alternatively, (figure 3) the two outer resonators may be rotated by 180 DEG in relation to one another. The arrangement is stated to reduce crosstalk. <IMAGE>

Description

v -1 2279182 MICROWAVE CERAMIC FILTER The present invention relates to a

microwave ceramic filter.

A microwave ceramic filter may be constituted in principle, in the case of monolithic design, by at least two ceramic resonators which are formed within a one-piece ceramic body and coupled to one another. Within the ceramic body a resonator bore is provided for each ceramic resonator. The ceramic body is metallised on all sides, including the inner surfaces of the resonator bores, with the exception of an at least partly non-metallised end face. The individual ceramic resonators are coupled by way of the one-piece ceramic body itself.

Microwave ceramic filters of the type described above in general terms are known in principle, for instance from "IEEE Transactions on Microwave Theory and Techniques", Vol. MTT-34, No. 9, September 1986, pages 972 to 976. In this document the principle of such filters is in fact described on the basis of individual resonators, each within a ceramic body, which are coupled to one another via aperture windows. However, the principle can readily be applied to monolithic filters, whereby the individual ceramic bodies of the resonators merge into a one-piece ceramic body. Such microwave ceramic filters are generally coupled to an external circuit in such a way that a coupling structure is provided on each of the two external ceramic resonators. Such a coupling structure can, f or instance, be provided by a capacitive coupling structure on a side of the ceramic body of the resonators that is separated from the remaining metal film. On the other hand it is also possible, for example, to provide coupling pins in the resonator bores of the outer ceramic resonators, via which coupling pins the filter can be coupled to an external 9 circuit.

In the case of filters of the type under discussion, such coupling structures have hitherto been provided on the same side of the filter. That is, the coupling structures are always provided on the same side of the particular ceramic body that is equipped with such a coupling structure and thereby in the event of coupling of the individual ceramic condensers are always situated on the same side. In order to avoid crosstalk, input and output wires leading to the filter must be electromagnetically separated, which is difficult, particularly given increasing miniaturisation.

The present invention seeks to provide a microwave ceramic filter of the type under discussion in which crosstalk is avoided by suitable design of the filter itself.

According to the present invention there is provided a microwave ceramic filter, in particular a monolithic filter without a casing, comprising at least two resonators coupled to one another, and a structure for coupling to an external circuit, wherein the resonators are arranged interdigitally.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a schematic representation of a microwave ceramic filter according to the invention containing two coupled ceramic resonators; Figure 2 is a schematic representation of a first embodiment of a microwave ceramic filter according to the invention containing three coupled ceramic resonators; Figure 3 is a schematic representation,of a second embodiment of a monolithic microwave ceramic filter 1 according to the invention containing three coupled ceramic resonators; Figure 4 shows a further embodiment of a microwave ceramic filter similar to the device shown in Figure 1. 5 In the case of the microwave ceramic filter shown in Figure 1, two ceramic resonators 1, 2 are coupled to one another within a one-piece ceramic body. These resonators 1 and 2 each contain a respective inner-conductor bore 3, 4, and an at least partly non-metallised end face 5. On these end faces 5 in the region of the inner-conductor bores 3, 4 there are provided shortening capacitors that are known in themselves. In the case of the ceramic filter 2 a shortening capacitor of this type is represented schematically as the metallic partial surface 6 surrounding inner-conductor bore 4. Each of the ceramic resonators 1, 2 also has a respective capacitive coupling structure 7, 8, also known in themselves.

In order to avoid crosstalk the two ceramic resonators 1, 2 are now arranged interdigitally. That is, the two ceramic resonators are rotated by 1800 in relation to one another, which can be gathered from the fact that the surfaces 5 which are partly free from metal film and also the coupling structures 7 and 8 are situated on opposite sides of the filter.

The microwave ceramic filter shown in Figure 2 is a monolithic three-pole filter with three ceramic resonators 10, 11, 12 which each have in the same way as the resonators shown in Figure 1, an inner-conductor bore 13, a surface 14 that is partly free from metal film, a shortening capacitor 15, and a coupling structure 16. With this embodiment the interdigital arrangement of the ceramic resonators for avoiding crosstalk is designed in such a way that the central ceramic resonator 12 is-rotated by 180' in relation to the two outer ceramic resonators 10 and 11 and the coupling structures 16 for the two outer ceramic resonators 10 and 11 are situated on the same side of the filter.

The microwave ceramic filter shown in Figure 3 is also a monolithic threepole filter with three ceramic resonators 20, 21, 22 which are coupled to one another and which, in the same way as the devices shown in Figures 1 and 2, each have an inner-conductor bore 23, a surface 24 that is partly free from metal film, and a shortening capacitor 25, as well as a coupling structure 26 on the two outer ceramic resonators 20 and 22.

In the case of this embodiment the interdigital arrangement of the ceramic resonators for avoiding crosstalk is achieved in that the two outer ceramic resonators 20 and 22 are rotated by 1800 in relation to one another and the coupling structures 26 are situated on the outer ceramic resonators 20 and 22 on opposite sides in relation to one another.

The microwave ceramic filter shown in Figure 4 largely corresponds to the embodiment shown in Figure 1. Corresponding parts are provided with the same reference numbers, and only the distinguishing characteristics are described.

The microwave ceramic filters according to the invention are distinguished by the fact that interdigitally coupled resonators are coupled very strongly, as a result of which broadband filters are formed. Narrowband filters with correspondingly higher damping can be realised by means of a slot provided on at least one side between resonators that are coupled to one another in one piece. In the case of the device shown in Figure 4, a slot 9 is provided between two resonators 1, 2 on both the top side and the underside of the filter. Such slots can be produced when the ceramic article is moulded or after sintering by means of a separating slot prior to metallisation.

Claims

1. A microwave ceramic filter, in particular a monolithic filter without a casing, comprising at least two resonators coupled to one another, and a structure for coupling to an external circuit, wherein the resonators are arranged interdigitally.

2. A microwave ceramic filter, in particular a monolithic filter without a casing, comprising at least two resonators coupled to one another, and a structure for coupling to an external circuit, wherein at least one of said resonators is oriented oppositely to the or each other resonator.

3. A microwave ceramic filter according to claim 1 or 2, having two coupled resonators wherein the two resonators have structures for external coupling provided on opposite sides thereof.

4. A microwave ceramic filter according to claim 1 or 2, with three coupled resonators wherein the central resonator is rotated by 1800 in relation to the outer resonators and the structure for external coupling is provided on the same side on each outer resonator.

5. A microwave ceramic filter according to claim 1 or 2, with three coupled resonators wherein the two outer resonators are rotated by 1800 in relation to one another and the structure for external coupling is provided on opposite sides on each outer resonator.

6. A microwave ceramic filter according to any preceding claim, wherein a slot is provided between the resonators on at least one side thereof.

7. A microwave ceramic filter, substantially as herein described with reference to, or as shown in, Figure 1, 2, 3 or 4 of the accompanying drawings.