Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-01-20
2001-04-17
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219100, C333S134000, C333S026000
Reexamination Certificate
active
06218914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter and a dielectric duplexer for use in a communication base station or the like.
2. Description of the Related Art
A dielectric filter relating to the present invention is shown in FIG.
7
. Although this dielectric filter is described in copending U.S. patent application Ser. No. 924,040, now U.S. Pat. No. 6,052,041, this dielectric filter was not known yet in the art at the time when the invention, on the basis of which the priority of the present invention is claimed, was filed as Japanese Patent Application No. H-10-8860.
FIG. 7
is a perspective view of the dielectric filter
110
. In this figure, an upper lid
114
is removed so that the internal structure can be seen. The dielectric filter shown herein is, by way of example, of the two-stage band-rejection filter type including two disk-shaped dielectrics
112
disposed side by side in a shielding cavity frame
111
.
The dielectric filter
110
includes a shielding cavity frame
111
formed of metal, a dielectric
112
disposed in the shielding cavity frame
111
, and external coupling means
120
. The dielectric
112
is formed of ceramic in a disk shape and electrodes are formed of silver or the like on two opposite upper and lower surfaces thereof. The lower surface of the dielectric
112
is fixed via solder or the like to the inner bottom surface of the shielding cavity frame
111
thereby achieving electric connection. The external coupling means
120
includes an electric probe
121
made of a metal wire. The electric probe
121
is disposed in such a manner that it extends in a space between the upper surface of the dielectric
112
and the shielding cavity frame
111
without having contact with either the dielectric
112
or the shielding cavity frame
111
. By employing the above structure, it becomes possible to reduce the current flowing through the shielding cavity frame
111
thereby reducing the loss due to such a current thus achieving a TM-mode dielectric filter having a small size in height and having high unloaded Q.
The electric probe
121
is connected via solder to an external connector
113
attached to the shielding cavity frame
111
so that a signal is input and output via the electric probe
121
. That is, a signal is supplied via a cable connected to the external connector
113
and is passed through the electric probe
121
. The electric probe
121
is coupled with the dielectric
112
via capacitance created between the electric probe
121
and the electrode of the dielectric
112
. The dielectric
112
coupled with the electric probe
121
has resonance and thus serves as a band-rejection filter. The resultant signal is output through a cable connected to another external connector
113
.
In the above-described dielectric filter, the coupling between the electric probe and the dielectric is realized via the capacitance between the electric probe and the dielectric. Thus, the strength of the coupling depends on the capacitance between the electric probe and the dielectric. The capacitance is determined by the distance between the electric probe and the dielectric, the areas of surfaces facing each other, and the dielectric constant of a substance existing between them. The attenuation varies with the change in the strength of the coupling, and the characteristic of the dielectric filter vary in such a manner that the filter has a band-rejection or bandpass characteristic with a wide bandwidth when the coupling is strong while the bandwidth becomes narrow when the coupling is weak. Therefore, to achieve a dielectric filter having desired characteristics, it is required to adjust the coupling between the electric probe and the dielectric. That is, it is required to adjust the capacitance between the electric probe and the dielectric.
In the above-described dielectric filter, the electric probe made of a metal wire is used as the external coupling means. The capacitance may be varied, as described above, by varying the distance between the electric probe and the dielectric, the areas of the surfaces, and/or the dielectric constant. However, it is difficult to change the location of the electric probe connected to the external connector because it is difficult to change the location of the external connector attached to the shielding cavity frame. The dielectric constant of air is impossible to change. Thus, a most practical manner of adjusting the capacitance between the electric probe and the dielectric is to change the length of the electric probe thereby changing the areas of the surfaces facing each other.
However, it is a troublesome process to adjust the length of the electric probe by cutting the electric probe for each dielectric or for each dielectric filter including the dielectric. Furthermore, if once the electric probe is cut to a too short length, it is impossible to make a readjustment to increase the capacitance.
Furthermore, an electrical discharge occurs through air existing between the electric probe and the dielectric when the potential difference between them exceeds the dielectric strength of air. Such a discharge can cause a difference in the characteristic of the electrode or the electric probe of the dielectric filter.
In view of the problems described above, it is an object of the present invention to provide a dielectric filter and dielectric duplexer whose characteristics can be more easily adjusted and which have higher reliability.
SUMMARY OF THE INVENTION
According to an aspect of the invention, to achieve the above object, there is provided a dielectric filter including a shielding cavity frame having electric conductivity, a dielectric having electrodes formed on two opposing faces and disposed in the shielding cavity frame, and external coupling means, wherein the external coupling means includes an electric probe at least a part of which is covered with a covering dielectric.
In this dielectric filter, the covering dielectric covering the electric probe is preferably movable.
The movability of the covering dielectric may be achieved by connecting the covering dielectric to the electric probe by means of mating via screw threads.
According to another aspect of the invention, there is provided a dielectric duplexer including a shielding cavity frame having electric conductivity, a dielectric having electrodes formed on two opposing faces and disposed in the shielding cavity frame, external coupling means, input/output connection means and antenna connection means connected to the coupling means, wherein the external coupling means includes an electric probe at least a part of which is covered with a covering dielectric.
In this dielectric duplexer, the covering dielectric covering the electric probe is preferably movable.
The movability of the covering dielectric may be achieved by connecting the covering dielectric to the electric probe by means of mating via screw threads.
In the above-described dielectric filter and the dielectric duplexer according to the invention, it is possible to easily adjust the capacitance between the electric probe and the dielectric. Furthermore, it is possible to increase the dielectric strength between the electric probe and the dielectric.
REFERENCES:
patent: 2431941 (1947-12-01), Kihn
patent: 4727342 (1988-02-01), Ishikawa et al.
patent: 4740764 (1988-04-01), Gerlack
patent: 6016090 (2000-01-01), Iio et al.
A. B. Bereskin: “Multi-Screw Tuner for Any Mismatch”, Microwave Journal, vol. 26, No. 8, Aug. 1983, pp. 133-141.
Patent Abstracts of Japan, vol. 8, No. 70 (E-235), Apr. 3, 1984 & JP 58 218201 A, (Alps Denki KK), Dec. 19, 1983.
Patent Abstracts of Japan, vol. 15, No. 58 (E-1032), Feb. 12, 1991 & JP 02 285702 A (Matsushita Electric Ind. Co. Ltd.), Nov. 26, 1990.
European Search Report dated Apr. 22, 1999.
Ise Tomoyuki
Kubota Kazuhiko
Jones Stephen E.
Lee Benny
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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