Dielectric resonator

Abstract: A dielectric resonator includes a cylindrical hole (4b) formed in the intersection of two resonator elements (2a,2b) forming a TM dual-mode dielectric resonator element (2). The hole (4b) extends in a direction across the thickness of the TM dual-mode dielectric resonator element (2). Furthermore, a quadrangular pyramid-shaped hole (4a) having a closed end is formed in each connecting part between each resonator element (2a,2b) and a cavity wall so that each hole (4a) extends from the outer surface of the cavity wall toward the inner portion of each resonator element (2), wherein the inner wall of each hole (4a) is covered with a conductor (3a) electrically connected to a cavity conductor (3). The shapes of the above holes (4a,4b) are determined so that the TM dual-mode dielectric resonator element (2) has the same resonance frequency for both TM 110 and TM 111 modes. The above arrangement makes it possible to provide a low-cost high-performance dielectric resonator having characteristics similar to those of a three-mode dielectric resonator, which can be produced in a small overall size.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric resonator comprising of a TM dual-mode dielectric resonator element disposed in a cavity. 2. Description of the Related Art Fig. 6 illustrates the structure of a conventional TM dual-mode dielectric resonator. In this and other figures, areas filled with dots represent those portions on which a conductor is formed. The dielectric resonator shown in Fig 6 comprises a TM dual-mode dielectric resonator arrangement 2 disposed in an integral fashion in a cavity 1 serving as a waveguide. The dielectric resonator arrangement 2 is made up of dielectric ceramic in such a manner that two rectangular resonator elements 2a and 2b each exhibiting resonance in a TM mode are integrated into one piece in a cross shape whereby the two resonator elements 2a and 2b are perpendicular to each other. The cavity 1 is formed with a rectangular-shaped frame of dielectric ceramic produced in an integral fashion together with the dielectric resonator arrangement 2 by molding wherein each open side of the frame is closed with a side plate (not shown). The whole outer surface of cavity 1 is coated with a cavity conductor 3 such as Ag. Each side plate is made up of a dielectric ceramic plate whose surface is covered with a conductor or made up of a conductive metal plate. Alternatively, each side plate may also be realized by means of utilizing a part of a metal case in which the dielectric resonator is disposed. The integration of two resonator elements 2a and 2b into one piece makes it possible to produce a dielectric resonator in a reduced size, in which the resonator elements 2a and 2b are formed so that the TM 110-mode resonance frequencies of the respective resonator elements 2a and 2b are substantially equal and thus the dielectric resonator serves as a TM 110 dual mode dielectric resonator. That is, this dielectric resonator acts as a two-stage dielectric resonator composed of two resonator elements. This type of dielectric resonator is used, for example, as a dielectric filter in a communication device. The above TM dual-mode dielectric resonator, however, is limited to a two-stage operation and it is impossible to achieve higher performance. It is also known in the art to realize a three-stage dielectric resonator with the same size as that of the two-stage dielectric resonator by combining three resonator elements having substantially equal resonance frequency in TM 110 mode into one piece in such a manner that the resonator elements are perpendicular to each other thereby forming a TM three-mode dielectric resonator. However, such a TM three-mode dielectric resonator has a complicated structure and therefore is difficult to produce, which results in extremely high cost. Document D4 (US 4,642,591) discloses a TM-mode dielectric resonance apparatus comprising at least two TM-mode dielectric resonators in a single case. Each resonator exhibits a TM110-mode. A metal coupling screw arranged in the interior of the case between both resonators serves to couple a degeneration TM111-mode of one resonator to the TM110 mode of the other resonator. Document D1 (JP-A-04296104) relates to a multiple mode dielectric resonator device having a conductive case in which a dielectric body consisting of two orthogonal dielectric members is arranged. The dielectric body has a hole into which a coupling adjustment member comprising a metallic screw can be inserted for tuning the resonance frequency. It serves as a TM110 dual-mode dielectric resonator. SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-performance low-cost dielectric resonator having characteristics similar to those of a three-mode resonator, which can be realized in a similar size without having to increase the size. The above and other objects are achieved by the present invention as described below. According to a first aspect of the present invention, there is provided a dielectric resonator including two dielectric resonator elements perpendicular to each other and disposed in an integral fashion in a cavity so as to form a TM dual-mode dielectric resonator arrangement, the dielectric resonator having a hole formed in the TM dual-mode dielectric resonator arrangement, that the hole extending from the outer surface of the cavity wall toward the inner portion of the TM dual-mode dielectric resonator arrangement along its axis, the inner wall of the hole being covered with a conductor electrically connected to a cavity conductor, the hole being formed so that the TM 110-mode resonance frequency of the TM dual-mode dielectric resonator arrangement is substantially equal to the TM 111-mode resonance frequency. According to a second aspect of the present invention, there is provided a dielectric resonator including two dielectric resonator elements perpendicular to each other and disposed in an integral fashion in a cavity so as to form a TM dual-mode dielectric resonator arrangement, the dielectric resonator having a hole formed in the intersection of the two dielectric resonator elements of the TM dual-mode dielectric resonator arrangement, the hole being formed so that the TM 110-mode resonance frequency of the TM dual-mode dielectric resonator arrangement is substantially equal to the TM 111-mode resonance frequency. According to a third aspect of the present invention, there is provided a dielectric resonator including two dielectric resonator elements perpendicular to each other and disposed in an integral fashion in a cavity so as to form a TM dual-mode dielectric resonator arrangement, the dielectric resonator having a first hole formed in the TM dual-mode dielectric resonator arrangement the first hole extending from the outer surface of the cavity wall toward the inner portion of the TM dual-mode dielectric resonator element along its axis, the inner wall of the first hole being covered with a conductor electrically connected to a cavity conductor; and a second hole being formed in the intersection of the two dielectric resonator elements of the TM dual-mode dielectric resonator element, the first and second holes being formed so that the TM 110-mode resonance frequency of the TM dual-mode dielectric resonator arrangement is substantially equal to the TM 111-mode resonance frequency. In the present invention, the hole(s) is (are) formed in a proper form and at a proper location in the TM dual-mode dielectric resonator arrangement so that the TM dual-mode dielectric resonator has the same resonance frequency for both TM 110 and TM 111 modes thereby achieving high performance similar to that of a conventional TM three-mode dielectric resonator without having to increase the overall size. In the present invention, if the shape and/or the location of the hole or holes formed in the TM dual-mode resonator arrangement are changed, the capacitance of the TM dual-mode resonator element arrangement changes and thus the resonance frequency associated with each TM mode also changes. As will be described in greater detail later, the change in resonance frequency associated with TM 110 mode occurs at a different fashion from that of TM 111 mode, and it is possible to obtain the same resonance frequency for both TM 110 and TM 111 modes by properly selecting the shape and/or the location of the hole. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) is a perspective view illustrating the external appearance of a first embodiment of a dielectric resonator according to the invention, and Fig. 1(b) is a side view thereof; Fig. 2 illustrates the relation between the depth of a hole formed in the dielectric resonator shown in Fig. 1 and its TM 110-mode and TM 111-mode resonance frequencies; Fig. 3(a) is a perspective view illustrating the external appearance of a second embodiment of a dielectric resonator according to the invention, and Fig. 3(b) is a cross-sectional view thereof taken along line X-X; Fig. 4 illustrates the relation between the diameter of a hole formed in the dielectric resonator shown in Fig. 3 and its TM 110-mode and TM 111-mode resonance frequencies; Fig. 5 is a perspective view illustrating the external appearance of a third embodiment of a dielectric resonator according to the invention; Fig. 6 is a perspective view illustrating the external appearance of a conventional dielectric resonator; and Fig. 7 is a partially cutaway perspective view of a dielectric resonator which is a variation of the third embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described in further detail below with reference to preferred embodiments in conjunction with the accompanying drawings. In the figures, similar parts to those of the figure representing the conventional resonator are shown by similar reference numerals. Fig. 1 illustrates the structure of a first embodiment of a dielectric resonator according to the present invention wherein Fig. 1(a) is a perspective view illustrating the external appearance and Fig. 1(b) is a side view of the dielectric resonator shown in Fig. 1(a). As shown in Figs. 1(a) and 1(b), the dielectric resonator of this embodiment includes a cross-shaped TM dual-mode dielectric resonator element arrangement 2 disposed in an integral form in a cavity 1. The TM dual-mode dielectric resonator arrangement 2 is composed of resonator elements 2a and 2b both ends of each of which are connected to the wall of the cavity 1. A hole 4a with a closed end is formed in a central part of each connecting portion between each resonator element 2a, 2b and the cavity wall in such a manner that each hole 4a extends from the outer surface of the cavity wall toward the inner portion of each resonator element 2a, 2b. The inner wall of each hole 4a is covered with a conductor 3a which is electrically connected to the cavity conductor 3. In the present embodiment, as described above, holes 4a are formed along the axes of the respective resonator elements 2a and 2b and the cavity conductor 3 also extends over the inner surface of each hole 4a. The conductor 3a is thus a part of the cavity conductor 3. The geometric structure, that is, the diameter and the depth of each hole 4a are selected so that the TM dual-mode dielectric resonator arrangement 2 has the same resonance frequency for both TM 110 and TM 111 modes. The other parts except for the holes 4a are constructed in the same manner as in the conventional resonator shown in Fig. 6 and thus they are not described in further detail here. Fig. 2 illustrates the changes in resonance frequencies in TM 110 and TM 111 modes as a function of the depth of the hole 4a formed in accordance with the present embodiment. In the present embodiment, with the increase in the depth of the hole 4a, the distance between the opposite ends of the dielectric resonator arrangement 2 decreases and thus the capacitance of the dielectric resonator element 2 increases. With the increase in the capacitance, the resonance frequency decreases in both TM 110 and TM 111-modes as shown in Fig. 2. Although the TM 111-mode has a higher resonance frequency than the TM 110-mode in a shallow depth range, the TM 111-mode resonance frequency decreases at a greater rate with the increase in the depth of the hole 4a than the TM 110-mode resonance frequency. Therefore, the TM 111-mode resonance frequency becomes the same as the TM 110-mode resonance frequency at a certain depth. According to the present embodiment, as can be understood from the above discussion, it is possible to set the TM 110-mode and TM 111-mode resonance frequencies so that they have the same value by properly selecting the diameters and the depths of the holes 4a. Fig. 3 illustrates the structure of a second embodiment of a dielectric resonator according to the present invention wherein Fig. 3(a) is a perspective view illustrating its external appearance and Fig. 3(b) is a cross-sectional view of the dielectric resonator shown in Fig. 3(a) taken along line X-X. In the dielectric resonator according to the embodiment shown in Figs. 3(a) and 3(b), a hole 4b having a circular shape in cross section is formed in a central portion of a dielectric resonator arrangement 2 at which two resonator elements 2a and 2b cross each other. The hole 4b extends through the dielectric resonator arrangement 2 in a direction (in a vertical direction in Fig. 2) across its thickness from one side to the opposite side. The diameter of the hole 4b is selected so that the TM dual-mode dielectric resonator arrangement 2 has the same resonance frequency for both TM 110 and TM 111-modes. The other parts except the hole 4b are constructed in the same manner as in the conventional dielectric resonator shown in Fig. 6 and they are not described in further detail here. Fig. 4 illustrates the changes in resonance frequencies in TM 110 and TM 111-modes as a function of the diameter of the hole 4b formed in accordance with the present embodiment. In this second embodiment, the capacitance of the dielectric resonator arrangement 2 decreases with the increase in the diameter of the hole 4b. With the decrease in the capacitance, both the TM 110-mode and TM 111-mode resonance frequencies increase as shown in Fig. 4. Although the TM 110-mode has a lower resonance frequency than the TM 111-mode in a small-diameter range, the TM 110-mode resonance frequency increases at a greater rate with the increase in the diameter of the hole 4b than the TM 111-mode resonance frequency. Therefore, the TM 110-mode resonance frequency is the same as the TM 111-mode resonance frequency at a certain diameter. According to this embodiment, as can be understood from the above discussion, it is possible to set the TM 110-mode and TM 111-mode resonance frequencies so that they have the same value by properly selecting the diameter of the hole 4b. Although in the specific example described above the hole is formed through the dielectric resonator arrangement such that it extends from one side to the opposite side of the resonator arrangement, the hole may also be formed in such a manner that it has a closed end. Fig. 5 is a perspective view illustrating the structure of a third embodiment of a dielectric resonator according to the present invention. In the dielectric resonator according to the embodiment, shown in Fig. 5, a hole 4b having a circular shape in cross section is formed in the intersection of two resonator elements 2a and 2b wherein the hole 4b extends through the dielectric resonator arrangement 2 in a direction across its thickness. Furthermore, a hole 4a, for example, quadrangular pyramid-shaped hole 4a having a closed end, is formed in each connecting part between each resonator element 2a, 2b and a cavity wall 1 in such a manner that each hole 4a extends from the outer surface of the cavity wall toward the inner portion of each resonator element 2a, 2b. The inner wall of each hole 4a is covered with a conductor 3a which is electrically connected to the cavity conductor 3. The shape of the holes 4a and 4b are determined so that the TM dual-mode dielectric resonator arrangement 2 has the same resonance frequency for both TM 110 and TM 111-modes. The other parts except for the holes 4a and 4b are constructed in the same manner as in the conventional resonator shown in Fig. 6 and thus they are not described in further detail here. The dielectric resonator of the embodiment of Fig. 5, as described above, has a structure obtained by combining the structures of the first and second embodiments. This structure allows the capacitance of the dielectric resonator arrangement 2 to be set in a more flexible manner than in the previous embodiments. In this embodiment, it is possible to set the TM 110-mode and TM 111-mode resonance frequencies so that they have the same value by properly selecting the inner diameters, the locations, and the depths of the holes 4a formed along the axes of the dielectric resonator arrangement 2 and of the hole 4b formed across its thickness. In each embodiment described above, the holes 4a and 4b may be formed simultaneously in the process in which the dielectric resonator is formed, or may be formed by cutting or the like after forming the dielectric resonator. Although in the specific embodiments described above, the dielectric resonator arrangement 2 is formed in an integral fashion in the cavity, the dielectric resonator arrangement and the cavity may also be formed separately and then combined into a single piece with a silver-filled adhesive or the like. Furthermore, the cavity itself may also be formed by combining six separately-formed ceramic plates coated with a conductor into a single piece with a silver-filled adhesive or the like. A metal case may also be employed to form the cavity. In the dielectric resonator according to the above embodiments of the invention, the hole(s) is (are) formed in a proper shape and at a proper location in the TM dual-mode resonator arrangement so that the TM 110-mode resonance frequency of the TM dual-mode resonator arrangement is equal to the TM 111-mode resonance frequency. This makes it possible to easily achieve high performance similar to that of a conventional TM three-mode dielectric resonator. Thus it is possible to produce a small-sized high-performance dielectric filter using a dielectric resonator according to the present invention. Fig. 7 illustrates the structure of a dielectric resonator which is a variation of the third embodiment of the invention. In Fig. 7, a part of the dielectric resonator is cut away so as to show the internal structure of a hole. In the dielectric resonator of the embodiment shown in Fig. 7, an elliptic cone-shaped hole 4a is formed in each connecting part between each end of two resonator elements 2a and 2b and a cavity wall 1 in such a manner that each hole 4a extends from the outer surface of the cavity wall 1 toward the inner portion of each resonator element 2a, 2b. The inner wall of each hole 4a is covered with a conductor 3a electrically connected to a cavity conductor 3. The shape of each hole 4a is determined so that the TM 110-mode resonance frequency of the TM dual-mode dielectric resonator arrangement 2 is equal to the TM 111-mode resonance frequency. The other parts except for the holes 4a are constructed in the same manner as in the conventional resonator shown in Fig. 6 and thus they are not described in further detail here. The dielectric resonator of the present embodiment is different from the third embodiment described above in that the holes 4a are formed in a different shape. In the embodiment of Fig. 7, it is possible to set the TM 110-mode and TM 111-mode resonance frequencies so that they have the same value by properly selecting the inner diameters, the locations, and the depths of the holes 4a formed from the cavity wall into the dielectric resonator arrangement 2 in directions perpendicular to the corresponding cavity wall, and also by properly selecting the size of the rectangular-shaped resonator and the relative dielectric constant ∈ r of the dielectric material.

Claims: A dielectric resonator including two dielectric resonator elements (2a,2b) arranged perpendicular to each other and disposed in a cavity (1) so as to form a TM dual-mode dielectric resonator arrangement (2), the dielectric resonator arrangement having a TM 110-mode resonance frequency and a TM 111-mode resonance frequency, said dielectric resonator having an inwardly extending hole (4a) formed in said TM dual-mode dielectric resonator arrangement (2), said inwardly extending hole (4a) extending from an outer surface of a wall of the cavity (1) toward an inner portion of said TM dual-mode dielectric resonator element arrangement (2) along an axis of the resonator arrangement (2), the inwardly extending hole (4a) having an inner wall, the cavity (1) having a conductor (3) disposed on walls of the cavity (1), the inner wall of said inwardly extending hole (4a) being covered with a conductor (3a) electrically connected to the cavity conductor (3), said inwardly extending hole (4a) being formed so that the TM 110-mode resonance frequency of said TM dual-mode dielectric resonator arrangement (2) is substantially equal to the TM 111-mode resonance frequency. A dielectric resonator including two dielectric resonator elements (2a,2b) arranged perpendicular to each other and having an intersection portion where the two elements (2a,2b) intersect and further being disposed in a cavity (1) so as to form a TM dual-mode dielectric resonator arrangement (2), the dielectric resonator arrangement (2) having a TM 110-mode resonance frequency and a TM 111-mode resonance frequency, said dielectric resonator having an intersection hole (4b) formed at the intersection portion of said two dielectric resonator elements (2a,2b), said intersection hole (4b) being formed so that the TM 110-mode resonance frequency of said TM dual-mode dielectric resonator arrangement is substantially equal to the TM 111-mode resonance frequency. A dielectric resonator including two dielectric resonator elements (2a,2b) arranged perpendicular to each other and having an intersection portion where the two elements (2a,2b) intersect and further being disposed in a cavity (1) so as to form a TM dual-mode dielectric resonator arrangement (2), the dielectric resonator arrangement (2) having a TM 110-mode resonance frequency and a TM 111-mode resonance frequency, said dielectric resonator having an inwardly extending hole (4a) formed in said TM dual-mode dielectric resonator arrangement (2), said inwardly extending hole (4a) extending from an outer surface of a wall of the cavity (1) toward an inner portion of said TM dual-mode dielectric resonator element (2) along an axis of a resonator element, the inwardly extending hole (4a) having an inner wall, the cavity (1) having a conductor (3) disposed on walls of the cavity (1), the inner wall of said inwardly extending hole (4a) being covered with a conductor (3a) electrically connected to the cavity conductor (3); and further having an intersection hole (4b) formed at the intersection portion of said two dielectric resonator elements (2a,2b) said inwardly extending and intersection holes (4a,4b) being formed so that the TM 110-mode resonance frequency of said TM dual-mode dielectric resonator arrangement (2) is substantially equal to the TM 111-mode resonance frequency. The dielectric resonator of claim 1 or 3, wherein said cavity (1) comprises a substantially rectangular structure housing said dielectric resonator elements (2a,2b), each element (2a,2b) contacting an inner wall of the cavity (1) at opposite first and second ends, a plurality of inwardly extending holes (4a) being provided such that a inwardly extending hole (4a) extends from the outer wall of the cavity (1) toward respective ones of the first and second ends. The dielectric resonator of claim 1 or 3 , wherein the depth of the inwardly extending hole (4a) is selected so that the TM 110 resonance frequency and the TM 111 resonance frequency are substantially the same. The dielectric resonator of claim 4, wherein the depths of each of the inwardly extending holes (4a) is selected so that the TM 110 resonance frequency and the TM 111 resonance frequency are substantially the same. The dielectric resonator of claim 1, wherein the TM 110 and TM 111 resonance frequencies decrease as the depth of the inwardly extending hole (4a) increases. The dielectric resonator of claim 2, wherein said cavity (1) comprises a substantially rectangular structure housing said dielectric resonator elements (2a,2b), each resonator element (2a,2b) contacting a wall of the cavity (1) at first and second opposite ends. The dielectric resonator of claim 2 or 3, wherein the diameter of the intersection hole (4b) is selected so that the TM 110 resonance frequency and TM 111 resonance frequency are substantially the same. The dielectric resonator of claim 2 or 3, wherein the TM 110 and the TM 111 resonance frequencies increase as the diameter of said intersection hole (4b) increases. The dielectric resonator of claim 2 or 3, wherein said intersection hole (4b) extends completely through the intersection portion of said dielectric resonator element (2). The dielectric -resonator of one of claims 1 to 11 wherein the frequency at which the TM dual-mode dielectric resonator element (2) resonates in both TM 110 and TM 111-modes is selected within the range from 800 to 1000 MHz. The dielectric resonator of claim 12, wherein the inwardly extending hole (4a) whose inner surface is covered with the conductor (3a) electrically connected to said cavity conductor (3) is formed in the shape of an elliptic cone. The dielectric resonator of claim 3, wherein the inwardly extending hole (4a) is tapered so as to decrease in cross section closer to a dielectric resonator element (2). The dielectric resonator of claim 14, wherein the inwardly extending hole (4a) is cone shaped. The dielectric resonator of claim 14, wherein the inwardly extending hole (4a) is pyramid shaped. The dielectric resonator of claim 3, wherein the TM 110 and TM 111 resonance frequencies decrease as the depth of said inwardly extending hole (4a) increases and increase as the diameter of the intersection hole (4b) increases. The dielectric resonator of one of claims 1 to 17, wherein the two dielectric resonator elements (2a,2b) are disposed in the cavity (1) integral therewith. The dielectric resonator of one of claims 1 to 18, wherein the cavity (1) comprises an integral member. The dielectric resonator of one of claims 1 to 18, wherein the cavity comprises a plurality of separate pieces joined together into a unitary structure.

Inventors: ABE SHIN, HATTORI JUN, KURISU TORU, ABE, SHIN, HATTORI, JUN, KURISU, TORU
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1997
Main classification: H01P7
IPC codes: H01P7, H01P1