Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1996-03-25
1998-03-31
Pascal, Robert
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333222, 333203, H01P 1202, H01P 704
Patent
active
057343063
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/FI94/00398 filed Sep. 12, 1994.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The object of the present invention is a coaxial resonator construction in which a center conductor is coaxially surrounded by a conductive shield. An insulating layer is situated between the center conductor and the shield. The insulating layer may be ceramic or air, for example.
2. Description of the Prior Art
It is known that a coaxial resonator can be manufactured from a ceramic block that has a bottom surface, a top surface and side surfaces. A hole that is plated with a conductive material passes through the ceramic block from the top surface to the bottom surface. This hole forms the center conductor of the resonator. The shield is formed by a plating of conductive material on the outer surfaces of the ceramic block. The plating on the outer surface covers the side surfaces and most of the bottom surface. There is no plating on the top surface of the ceramic block at least near the hole that forms the center conductor. The plating of the center conductor is connected to the plating of the shield at the bottom surface of the block. A coaxial resonator that is created from a ceramic block is also called a ceramic resonator.
Ceramic resonators are especially useful in radio frequency devices with a frequency range that extends beyond 1000 MHz. At very high frequencies, the length of the center conductor of a resonator may be only a few millimeters, which is approximately equal to one quarter of the wavelength.
The manufacturing process of ceramic resonators is problematic. It is difficult to machine a ceramic block because ceramic is a very hard material. A different special tool that presses the resonator into its final shape and makes the hole into the ceramic block must be manufactured for producing each different size of ceramic resonator. After the ceramic mixture has been formed, the excess components of the mixture are burned off and finally the ceramic block is sintered at approximately 1200.degree. C. The special tools used in the manufacturing process are expensive and machining the ceramic material wears the tools quickly. Because of tool wear, the dimensions of the ceramic blocks change, whereupon, for example, an optimal ratio between the diameter of the shield and the diameter of the center conductor formed by the conductive material-plated hole in the ceramic block is no longer achieved. This causes changes in the electrical characteristics of the resonator. The punches that are used to make the holes in very small resonators are so thin that they cannot withstand the pressure that is used in the manufacturing process and consequentially break easily.
It is also difficult to manufacture a filter. In the manufacturing process of a filter, several holes that function as resonators are made in each ceramic block. The degree of inductive and capacitive coupling between the holes is controlled by placing the holes at suitable distances from each other. The degree of coupling between the resonators of the filter does not always meet specifications due to the manufacturing process and the tools used. Prior art offers several methods and constructions for controlling the degree of coupling between the resonators. The degree of coupling can be controlled with the pattern of the conductor on the surface of the ceramic block, as described in Finnish patent specification 87407. None of the known methods can remove the problem, i.e., can "move a hole from one place to another." A faulty component must often be rejected, resulting in lower production line output.
Another manufacturing problem is related to the manufacture of the tool itself. The first version of the tool usually does not meet the specifications compiled for it, and therefore the dimensions of a resonator that is made with the tool may not meet the specifications set for it. The sintering process in particular may cause shrinkage that is difficult to estimate beforehand. If the tool i
REFERENCES:
patent: Re34898 (1995-04-01), Turunen et al.
patent: 5160905 (1992-11-01), Hoang
patent: 5331300 (1994-07-01), Shimizu et al.
Jantunen Heli
Turunen Aimo
ADC Solitra Oy
Pascal Robert
Summons Barbara
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