Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-06-08
2001-11-20
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S203000, C333S222000
Reexamination Certificate
active
06320482
ABSTRACT:
TECHNOLOGICAL FIELD
The invention relates generally to the structures of resonator filters used at frequencies of hundreds of megahertz and several gigahertz. Particularly the invention relates to a filter structure which consists of a small number of integral components, and to a method for manufacturing a filter of this kind.
BACKGROUND OF THE INVENTION
Regarding mobile communication systems the essential operating frequencies are located in a frequency domain, which extends from hundreds of megahertz to several gigahertz, and in microwave links between the stationary parts of the network, even to tens of gigahertz. The filters which are used at these frequencies are generally based on resonators comprising an inner conductor surrounded by an outer conductor. The resonators are divided into different types, usually on the basis of structural details. Known resonator types are for instance the helix, the coaxial, the microstrip and the dielectric resonators; the filters are correspondingly called helix, coaxial, microstrip and dielectric filters. The filter resonators are also called filter stages or filter circuits.
FIG. 1
is a schematic cross-section of a known coaxial filter having three resonators. The inner conductors
101
of the resonators are fastened at one end (in the figure the lower end) to a printed circuit board
102
so that the printed circuit board has a hole
103
for each inner conductor, into which hole the lower end of the inner conductor is pushed. On the bottom surface of the printed circuit board
102
there is a substantially continuous ground plane
104
, which after the assembly is connected in an electrically conducting manner (for instance by solder) to the lower end of each inner conductor. The top surface of the printed circuit
102
board comprises electrically conducting patterns
105
, which arrange the connections from a filter input port to the resonator which is closest to the input port, and correspondingly to the filter's output port from the resonator which is closest to the output port. The patterns
105
can further have an effect on the electromagnetic couplings between the resonators. The inner conductors are enclosed in an electrically conducting box structure
106
which forms the outer conductor of each resonator and which at the same time acts as the mechanical outer cover of the filter. At the edges it is connected to the ground plane
104
on the bottom surface of the printed circuit board
102
. The input and output ports of the filter are isolated from the electrically conducting outer cover.
A relatively large number of components is typical for the prior art filter structures. This causes inconvenience in the assembly because the large number of separate components increases manufacturing costs and tends to cause dimensioning variations in the final products. Further it is typical to the prior art filter structures comprising several components that they have intermodulation problems, which means a non-linear mixing of two or more signals and the non-harmonic frequencies resulting from the mixing. The connection surfaces of the separate components connected to each other form a significant source of intermodulation, particularly when the signals have a high power level. The rusty bolt effect means a phenomenon where contact surfaces, not well matched to each other, an insufficient tightening torque, oxidation, corrosion, impurities on the contact surfaces, or some other factor, results in that the electrically conducting continuous surfaces in the junction between two metal bodies are not tightly abutting each other. Then there exists a substantial uncontrolled resistance and/or capacitance between them, which causes non-linear current-voltage effects in the electric current passing through the junction. The non-harmonic frequencies generated by the intermodulation can be extremely harmful, for instance if they happen to overlap a useful signal.
SUMMARY OF THE INVENTION
The object of the present invention is to present a resonator and filter structure which consists of relatively few components and where the disadvantages caused by the junctions between separate parts are minimised. An object of the invention is also to present a resonator and filter structure which is favourable regarding the manufacturing techniques. A further object of the invention is to present a method for manufacturing the resonator and filter structure according to the invention.
The objects of the invention are attained by manufacturing a resonator and a filter, which comprises resonators, of substantially two body components, of which the first one comprises a substantial part of the inner conductor or inner conductors as well as the bottom and side walls of the box structure, and of which the second one comprises the lid of the box structure and possibly some coupling means affecting the electromagnetic characteristics of the resonators.
A resonator according to the invention is characterised in that it comprises a first part and a second part, of which the first part comprises at least a part of the inner conductor and a part of the outer conductor which is integral with the inner conductor and made of the same material, and of which the second part comprises such a part of the outer conductor which, when connected to the first part, forms a continuous outer conductor enclosing the inner conductor.
A filter according to the invention is characterised in that it comprises a first part and a second part, of which the first part comprises at least a part of the inner conductors of the resonators as well as a part of the outer conductor, which is integral with the inner conductors and made of the same material, and of which the second part comprises such a part of the outer conductor which, when connected to the first part, forms a continuous outer conductor enclosing the inner conductors.
The invention relates also to a method which is characterised in that it comprises steps in which
a first integral part is formed in one operation, so that the first part comprises at least a part of the inner conductor and a part of the outer conductor, which is integral with the inner conductor and made of the same material,
a second integral part is formed in one operation, so that the second part comprises a part of the outer conductor, and
the first and the second parts are attached to each other so that they form a continuous outer conductor enclosing the inner conductor.
According to the invention two integral bodies are manufactured, of which the first body comprises an essential part of the inner conductors of the resonator or resonators as well as an essential part of the electrically conducting box structure surrounding the inner conductors. The second part comprises the rest of the box structure, and it is attached to the first part so that an integral box structure is formed. If the structure comprises two or more resonators, then the first and/or the second part further comprises coupling and/or matching means, which have an effect on the electromagnetic characteristics of the resonators and on the electromagnetic couplings between the resonators.
The second part can also comprise a part of an inner conductor or inner conductors, whereby a complete inner conductor is formed only when the parts are attached to each other. In such a case the inner conductor sections contained in the different parts can even have a different thickness, whereby an impedance step of the inner conductor is formed at the joint between the parts.
Extruding is a preferred method for manufacturing the first and second parts. A metallic or metal containing, or a raw material which otherwise has a good electrical conductivity, is pressed at a high pressure into a mould, whereby it gets the desired form, and its different sections, such as the inner conductors and the grounding substrate connected to one end of the inner conductors, are seamlessy attached to each other. An extruded article can be very exactly dimensioned, also in series production. The interface between t
Ala-Kojola Jouni
Korpela Juha
Lohtander Kari
Mikkonen Esa
Darby & Darby
Jones Stephen E.
LK-Product Oy
Pascal Robert
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