Patent Publication Number: US-6218914-B1

Title: Dielectric filter and dielectric duplexer including a movable probe

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a dielectric filter according to the present invention; 
     FIG. 2 is a perspective view of external coupling means according to the present invention; 
     FIG. 3 is a perspective view of a second embodiment of a dielectric filter according to the present invention; 
     FIG. 4 is a perspective view of external coupling means of the second embodiment according to the present invention; 
     FIG. 5 is a perspective view of a third embodiment of a dielectric filter according to the present invention; 
     FIG. 6 is a perspective view of a dielectric duplexer according to the present invention; and 
     FIG. 7 is a perspective view of an another type of dielectric filter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, an embodiment of a dielectric filter according to the present invention is described below. FIG. 1 is a perspective view of the dielectric filter  10  according to the present invention. In the figure, an upper lid  14  is removed so that the internal structure can be seen. 
     The dielectric filter  10  includes a shielding cavity frame  11 , disk-shaped dielectrics  12 , and external coupling means  20 . The shielding cavity frame  11  is formed of metal and external connectors  13  are attached to it so that a signal is input and output from and to the outside via cables. The external coupling means  20  are connected to the respective external connectors  13  via solder. Each dielectric  12  is formed of ceramic in a disk shape and electrodes are formed on it by means of coating and baking silver paste on two opposing surfaces. The lower surface of each dielectric  12  is fixed via solder or the like to the inner bottom face of the shielding cavity frame  11  thereby achieving electric connection. Alternatively, the dielectric  12  may be soldered to a ground plate or the like and may be placed in the shielding cavity frame  11 . In this embodiment, two dielectrics  12  are placed side by side and these two dielectrics  12  are connected to each other via a ¼-transmission line  15  so that the dielectric filter  10  acts as a two-stage band-rejection filter. The shielding cavity frame  11  may also be produced by forming an electrically conductive layer on the surface of a ceramic material. The dielectric  12  may also be formed into a square shape. The electrodes on the two opposing surfaces of the dielectric  12  may be formed into the structure of a multilayer thin film so as to reduce the loss. 
     The external coupling means  20  includes an electric probe  21  made up of a metal wire a desired part of which is covered with a resin or the like  22  serving as a covering dielectric. As for the resin  22 , polyprene or a similar resin is employed which can be easily formed into a desired shape and which has elasticity which makes it easy to perform the adjustment which will be described later. The resin  22  is formed into the shape of a cylinder with a diameter greater than the diameter of the electric probe  21  wherein a through-hole is formed such that it extends from one end of the cylinder to the opposite end or a semi-through-hole is formed such that one end of the semi-through-hole is closed with one end of the cylinder. The electric probe  21  is inserted into this hole and the resin  22  is moved to a desired position so that a desired part of the electric probe  21  is covered with the resin  22  as shown in FIG.  2 . Thus, the resin  22  is present between the electric probe  21  and the dielectric  12 . The resin  22  has a higher dielectric strength and a greater dielectric constant than air. Therefore, covering the electric probe  21  with the resin  22  results in a reduction in the probability that a discharge will occur between the electric probe  21  and the dielectric  12 . Furthermore, the capacitance can be varied by varying the dielectric constant between the electric probe  21  and the dielectric  12  using the resin  22 . More specifically, by varying the relative length of the part of the electric probe  21  inserted in the resin  22 , it is possible to vary the capacitance and thus the strength of the coupling between the electric probe  21  and the dielectric  12 . Thus it becomes possible to make an adjustment to obtain desired band characteristics. 
     Referring now to FIGS. 3 and 4, a second embodiment of the present invention is described below. Similar parts to those in the previous embodiment are denoted by similar reference numerals and they are not described in further detail herein. 
     As illustrated in FIG. 3, the dielectric filter of the present embodiment includes two disk-shaped dielectrics  12  each having electrodes formed on two opposing surfaces and disposed side by side in a shielding cavity frame  11 . The two dielectrics  12  are coupled to each other via a capacitive coupling member  16 . The dielectric filter  10   a  having the structure described above acts as a two-stage bandpass filter. 
     FIG. 4 is a perspective view illustrating an electric probe  21   a  made up of a metal wire and also illustrating a resin  22   a  covering the electric probe  21   a , according to the present embodiment. As shown in FIG. 4, the electric probe  21   a  and the resin  22   a  are threaded such that the electric probe  21   a  serves as a male screw and the resin  22   a  acts as a female screw. The resin  22   a  is screwed onto the electric probe  21   a  thereby connecting them to each other. This allows the resin  22   a  to be easily connected to the electric probe  21   a  in a firm fashion so that the resin  22   a  is not moved by external vibrations or a mechanical shock. That is, the strength of the coupling between the electric probe  21   a  and the dielectric  12  is not changed by an external disturbance. 
     Referring now to FIG. 5, a third embodiment of the present invention is described below. Also in this figure, an upper lid  14  is removed so that the internal structure of a dielectric filter  10   b  can be seen. As in the first embodiment, two disk-shaped dielectrics  12  are connected to each other via a /4-transmission line  15  so that the dielectric filter  10   b  acts as a two-stage band-rejection filter. Similar parts to those in the previous embodiments are denoted by similar reference numerals and they are not described in further detail herein. 
     In the present embodiment, each external coupling means  20  includes an electric probe  21   b  made up of a metal wire a desired part of which is covered with a resin or the like  22   b  serving as a covering dielectric. As for the resin  22   b , polyprene or a similar resin is employed which can be easily formed into a desired shape and which has elasticity which makes it easy to perform the adjustment which will be described later. This resin  22   b  has a hole corresponding to the electric probe  21   b . The electric probe  21   b  is inserted into the hole and the resin  22   b  is moved to a desired position so that a desired part of the electric probe  21   b  is covered with the resin  22   b . Thus, the resin  22   b  is present between the electric probe  21   b  and the dielectric  12 . The resin  22   b  has a higher dielectric strength and a greater dielectric constant than air. Therefore, covering each electric probe  21   b  with the resin  22   b  results in a reduction in the probability that a discharge will occur between the electric probe  21   b  and the dielectric  12 . Furthermore, the capacitance can be varied by varying the dielectric constant between the electric probe  21   b  and the dielectric  12  using the resin  22   b . More specifically, by varying the relative length of the part of the electric probe  21   b  inserted in the resin  22   b , it is possible to vary the capacitance and thus the strength of the coupling between the electric probe  21   b  and the dielectric  12 . Thus, it is possible to make an adjustment such that the dielectric filter has desired characteristics. Because the external coupling means  20  is formed into the shape of a plate, it is easier to obtain desired capacitance than in the first embodiment. 
     Referring to FIG. 6, an embodiment of a dielectric duplexer according to the present invention is described below. Similar parts to those in the previous embodiments are denoted by similar reference numerals and they are not described in further detail herein. 
     As illustrated in FIG. 6, a dielectric duplexer  30  includes a first dielectric filter  31   a  and a second dielectric filter  31   b  wherein the first dielectric filter  31  includes two disk-shaped dielectrics  12   a   1  and  12   a   2  disposed in a shielding cavity frame  11  and the second dielectric filter  31  includes two disk-shaped dielectrics  12   b   1  and  12   b   2 . The two dielectrics  12   a   1  and  12   a   2  of the first dielectric filter  31   a  are coupled to each other via a capacitive coupling member  16   a  so that the first dielectric filter  31   a  serves as a transmitting bandpass filter. The two dielectrics  12   b   1  and  12   b   2  of the second dielectric filter  31   a  have resonant frequencies different from those of the dielectrics  12   a   1  and  12   a   2  of the first dielectric filter  31   a  and are coupled to each other via a capacitive coupling member  16   b  so that the second dielectric filter  31   b  serves as a receiving bandpass filter. The external coupling means  20   a  coupled with the dielectric  12   a   1  of the first dielectric filter  31   a  is connected to an external connector  13   a  which is connected to an external transmitting circuit. The external coupling means  20   d  coupled with the dielectric  12   b   2  of the second dielectric filter  31   b  is connected to an external connector  13   b  which is connected to an external receiving circuit. The external coupling means  20   b  coupled with the dielectric  12   a   2  of the first dielectric filter  31   a  and the external coupling means  20   c  coupled with the dielectric  12   b   1  of the second dielectric filter  31   b  are connected to an external connector  13   c  which is connected to an external antenna. 
     The external coupling means  20   a ,  20   b ,  20   c , and  20   d  each include an electric probe  21  made up of a metal wire a desired part of which is covered with a resin or the like  22  serving as a covering dielectric. By covering the electric probes  21  with resins  22 , it becomes possible to reduce the probability that a discharge will occur between the electric probes  21  and the dielectrics  12   a   1 ,  12   a   2 ,  12   b   1 , and  12   b   2 . Furthermore, the capacitance can be varied by varying the dielectric constant between the electric probe  21   s  and the dielectrics  12   a   1 ,  12   a   2 ,  12   b   1 , and  12   b   2 , using the resins  22 . More specifically, by varying the relative length of the part of the electric probes  21  inserted in the resins  22 , it is possible to vary the capacitance and thus the strength of the coupling between the electric probes  21  and the dielectrics  12   a   1 ,  12   a   2 ,  12   b   1 , and  12   b   2 . Thus it becomes possible to make an adjustment to obtain desired band characteristics. 
     As described above, the present invention has various advantages. That is, in the present invention, the electric probe made of metal and serving as the external coupling means in the dielectric filter or dielectric duplexer is covered with the covering dielectric thereby increasing the dielectric strength between the electric probe and the dielectric thus reducing the probability that a discharge will occur. 
     The covering dielectric on the electric probe is provided in a movable fashion whereby the part of the electric probe covered with the covering dielectric can be varied. This makes it possible to easily adjust the strength of the coupling between the electric probe and the dielectric without having to cut each electric probe to a shorter length. That is, by varying the coupling strength, it is possible to make an adjustment such that the pass band or the rejection band of the dielectric filter or the dielectric duplexer has a greater or smaller bandwidth as required. Thus, it is possible to easily produce dielectric filters and dielectric duplexers having desired characteristics depending on applications in which they are used. 
     Furthermore, by connecting the covering dielectric to the electric probe by means of mating via screw threads, it becomes possible to prevent the length of the part of the electric probe covered with the covering dielectric from varying after completion of the characteristic adjustment. That is, after adjusting the characteristics of the dielectric filter, the position of the covering dielectric on the electric probe is not varied by an external shock or vibrations. Thus, it is possible to prevent the dielectric filter and the dielectric duplexer from having a change in characteristics due to an external disturbance. 
     As described above, the present invention provides a dielectric filter and a dielectric duplexer whose characteristics can be easily adjusted and which have good long-term reliability.