Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1998-11-20
2001-01-30
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S212000, C333S249000, C029S600000
Reexamination Certificate
active
06181224
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 9704267-5 filed in Sweden on Nov. 21, 1997; the entire content of which is hereby incorporated by reference.
TECHNICAL FIELD
The present invention relates to a waveguide filter and a method of producing such a filter.
BACKGROUND
Filters of the waveguide type are conventionally made in the form of straight units, with one or more resonator cavities arranged along a straight centre line. The electrical path length of the integral resonator cavities and thus the waveguide filter as a whole is then the same as the mechanical length of the filter.
A disadvantage of such known waveguide filters is that their straight shape leads to certain requirements with regard to the size of the surface on which the filter is to be accommodated. If it is desired to reduce the surface area of the unit of which the waveguide filter is to form part, a limit is reached where conventional straight waveguide filters do not fit within the desired surface area of the unit.
From WO 93/01625, for example, a filter for electromagnetic waves, in particular microwaves, is previously known, in which circular cavities are angled relative to one another in groups, that is to say in such a manner that the filter as a whole does not follow a straight line. In this way, a certain flexibility is achieved as far as utilization of the space in, for example, a microwave unit is concerned. However, since the groups of cavities of which this filter consists are rectilinear, flexibility is reduced with regard to how the filter can be accommodated in another unit.
In the same manner, Japanese patent documents JP 58-161403 and JP 58-187001 disclose filter arrangements which comprise cavities that are not arranged in a straight line. The cavities described in these two documents are also circular, however, which reduces the flexibility with which the filter arrangements can be accommodated in another unit.
SUMMARY
A problem that is solved by the present invention is that of being able to reduce the area that is occupied by a waveguide filter.
Another problem that is solved by the present invention is that of increasing the possibilities of freely being able to position the input and output respectively of a waveguide filter.
A further problem that is solved by the invention is that of providing a method of producing a waveguide filter that occupies a smaller area than previously known waveguide filters of corresponding performance.
These problems are solved by a waveguide filter according to the invention being designed with an input and an output for the filter, and also one or more resonator cavities, at least one resonator cavity of which has a curved extension about its centre line. On account of this curved shape, the area required for the filter can be reduced.
For a curved resonator cavity, the electrical path length is determined essentially by the radius of curvature of the cavity, in other words the distance from the centre of curvature to the centre line of the resonator cavity. In order to obtain proper electrical characteristics of the filter as a whole, compensation for the mechanical length of the curved cavities must be carried out with respect to straight cavities with corresponding characteristics. This compensation is effected by first calculating the mechanical length of a straight cavity with the electrical characteristics that are desired for the curved cavity. Then, the mechanical length of the centre line of the curved cavity is compensated so as to allow for the fact that the cavity is curved.
By selecting the radius of curvature individually for the curved resonator cavities forming part of the filter, the input and output of the filter can be positioned in a desired manner.
In a preferred embodiment, the filter is designed as a band-pass filter, and forms part of the milled microwave block.
REFERENCES:
patent: 4439747 (1984-03-01), Kreinheder
patent: 4677402 (1987-06-01), Cesani et al.
patent: 4772863 (1988-09-01), Rosenberg et al.
patent: 5576674 (1996-11-01), Jachowski
patent: 5739734 (1998-04-01), Chen et al.
patent: 0736923 (1996-10-01), None
patent: 58-161403 (1983-09-01), None
patent: 58-187001 (1983-11-01), None
patent: 9301625 (1993-01-01), None
Burns Doane Swecker & Mathis L.L.P.
Lee Benny
Summons Barbara
Telefonaktiebolaget LM Ericsson (publ)
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