Dielectric resonator

Abstract: This dielectric resonator (10) comprises a cylindrical hollow case (12) made of metal, a cylindrical hollow dielectric resonator element (16) which is fixed and held in the case, a dielectric tuning unit (18) which is inserted into or withdrawn from a hollow portion (16a) of the dielectric resonator element, and the hollow portion of the dielectric resonator element is provided with cutout portions (17) which extend in their diameter directions. In this dielectric resonator, its effective dielectric constant as a whole can be varied by inserting the tuning unit into or withdrawing it from the hollow portion of the dielectric resonator element. In this case, when the tuning unit is withdrawn from the hollow portion of the dielectric resonator element, part of a path of an electric field at the dielectric resonator element is interrupted by the cutout portions.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a dielectric resonator according to the preamble of claim 1 and, more particularly, to the same which utilizes TE mode. Description of the Prior Art: One example of the conventional dielectric resonators which constitutes the background of this invention has been discloses, for example, in the specification of U.S. Patent No. 4,728,913. This conventional dielectric resonator is provided with a dielectric tuning unit which is capable of being inserted into or withdrawn from a hollow portion of a cylindrical hollow dielectric resonator element. In this conventional dielectric resonator, a rate of change of a resonance frequency is comparatively large, but a wider range for the resonance frequency adjustment has been required. A dielectric resonator is known from JP-A 62-166602, wherein a resonator element with a hollow section and a displaceable tuning unit are positioned in a conductor case allowing the adjustment of the resonance frequency. SUMMARY OF THE INVENTION A principal object of the present invention is to provide a dielectric resonator whose resonance frequency can be adjusted within a wider range than before. This object is solved by a dielectric resonator with the features contained in claim 1. Embodiments of the dielectric resonator according to the present invention are featured in the dependent claims. In this dielectric resonator, when the tuning unit is withdrawn from the hollow portion of the dielectric resonator element, part of a path of an electric field at the dielectric resonator element is interrupted by the cutout portion. Therefore, the effective dielectric constant of the dielectric resonator element decreases as compared with that of the conventional structure, and this results in increase in a variation of an effective dielectric constant as a whole. According to the present invention, the variation of the effective dielectric constant can be increased as a whole as compared with that of the conventional structure, therefore, the resonance frequency can be adjusted within a wider range than before. The above and other objects, features, aspects and advantages of this invention will be more apparent from the detailed description of the following embodiments when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B show the principle of the present invention, where Fig. 1A is an illustrated cross section view of a resonator 10 and Fig. 1B is an illustrated vertical section view of it. Fig. 2 is an illustrated cross section view showing one embodiment of the invention. Fig. 3 is an illustrated cross section view showing another embodiment of the present invention. Fig. 4 is an illustrated cross section view showing a modification of the embodiment of Fig.3. DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1A and 1B show the principle of the present invention, where Fig. 1A is an illustrated cross section view of a resonator 10 and Fig. 1B is an illustrated vertical section view of it. This dielectric resonator 10 comprises a cylindrical hollow case 12 made of, for example, metal. A cylindrical hollow supporting stand 14 made of a material of a low dielectric constant is provided on a bottom plate 12a of the case 12 at nearly the center of it. Further, a cylindrical dielectric resonator element 16 made of a high dielectric constant material such as ceramic is fixed on the supporting stand 14. Thus, the dielectric resonator element 16 is fixedly held within an outer (case 12) and as a whole the dielectric resonator 10 is formed which utilizes the TE 0lδ mode. In the center of this dielectric resonator element 16, a column shape space is formed and in this space two cutout portions 17 are formed each cross section of which has a U-shaped extending in the opposite directions of a diameter thereof and communicating with each other. That is, a hollow portion 16a of the dielectric resonator element 16 contains the two cutout portions 17 extending in the opposite directions of the diameter of the dielectric resonator element 16. In the hollow portion 16a of the dielectric resonator element 16, a cylindrical hollow tuning unit 18 is inserted which is made of a high dielectric constant material such as ceramic. The outer shape of this tuning unit 18 is made smaller than the inner shape of the hollow portion 16a of the dielectric resonator element 16. Thus, the tuning unit 18 can moves in the directions by arrows of Fig. 1B without touching with the inner peripheral surface of the hollow portion 16a of the dielectric resonator element 16. A supporting axis 20 made of a relatively low dielectric constant material such as ceramic is inserted into a hollow portion of the tuning unit 18, at which portion the supporting axis 20 and the tuning unit 18 are fixed. Thus, moving the supporting axis 20 axially, the tuning unit 18 is transfered in the directions indicated by the arrows of the Fig. 1B. Further, the bottom and top portions of the supporting axis 20 are respectively positioned at a penetrating hole of the bottom plate 12a and a penetrating hole of the top plate 12b of the case 12 by bushings 22a and 22b made of a low dielectric constant resin such as Teflon (Trademark) and are so supported that the axis 20 can move smmothly in the directions indicated by the arrows of Fig. 1B. The bottom plate 12a of the case 12 is provided with coaxial connectors 24a and 24b therethrough for input and output. Further, in the case 12, each one end of loop shape conductors 26a and 26b is connected to each inner conductor of the coaxial connectors 24a and 24b and each other end is connected to the case 12 to ground so that an external circuit can be magnetically coupled to the dielectric resonator element 16 through the conductors 26a and 26b. In this dielectric resonator 10, when the supporting axis 20 is axially moved, the tuning unit 18 made of dielectric material is transferred in the directions indicated by the arrows of Fig. 1B to be inserted into or withdrawn from the hollow portion 16a of the dielectric resonator element 16, as a result an effective dielectric constant is varied as a whole, thus a resonant frequency can be varied. In this case, when the tuning unit 18 is inserted into the hollow portion 16a of the dielectric resonator element 16, the effective dielectric constant of the dielectric resonator 10 increases as a whole, this results in decrease in a resonance frequency. On the other hand, when the tuning unit 18 is withdrawn from the hollow portion 16a of the dielectric resonator element 16, part of a path of electric field at the dielectric resonator element 16 is interrupted by the two cutout portions 17. Therefore the effective dielectric constant of the dielectric resonator element 16, that is, the effective dielectric constant as a whole decreases as compared with that of the conventional structure, and this results in increase in a resonance frequency. That is, in the dielectric resonator 10, the variation of the effective dielectric constant can be increased as a whole as compared with that of the conventional structure, therefore, the resonance frequency can be adjusted within a wider range. Further, an electric field distribution at the dielectric resonator element 16 is the most intense at about a center of the longest portion in a diameter direction (direction in thickness) of the dielectric resonator element 16. That is, the distribution is the most intense at about the center of the portion between the inside and outside diameters of the dielectric resonator element 16. In this dielectric resonator 10, because the cutout portions 17 are extended to the center, the variation of the resonance frequency can be effectively increased. In the conventional structures, the tuning unit is only an axis-symmetrical cylinder, therefore, electric energy generated by a rotating electric field tends to accumulate in the tuning unit. As a result, in the conventional structures, when the tuning unit is withdrawn from the hollow portion of the dielectric resonator element, energy due to the electric field tends to distribute more on the tuning unit side and thus a magnetic field also tends to distribute more on that side, resulting in increase in Joule's loss of the case end surface and then Q₀ is slightly decreased. However, in the dielectric resonator 10, the tuning unit 18 is not a mere cylinder but has a non-axis-symmetrical and two-rotation-symmetrical shape. Thus the electrical energy due to the rotating electric field shows almost no tendency to accumulate. Therefore, in the dielectric resonator 10, when the tuning unit 18 is withdrawn from the hollow portion 16a of the dielectric resonator element 16, the energy due to the electric field and the magnetic field are scarcely distributed and then Q₀ is scarcely reduced. Fig. 2 is an illustrated cross section view showing one embodiment of the invention. In this embodiment, six pieces of a cutout portion 17 with a nearly U-shaped cross section are formed which are extended radially in radius directions of a dielectric resonator element 16. The outer shape of a tuning unit 18 is formed somewhat smaller than the inner shape of a hollow portion 16a of the dielectric resonator element 16. That is, the hollow portion 16a formed in the dielectric resonator element 16 comprises six pieces of the cutout portion 17 which extend radially. When a number of the cutout portion 17 of the dielectric resonator element 16 is thus increased, a number of a place at which a path of an electric field of the dielectric resonator element 16 is interrupted increases when the tuning unit 18 is withdrawn from the hollow portion 16a of the dielectric resonator element 16. As a result a variation of the effective dielectric constant as a whole and a variation of the resonance frequency can be more expanded. Fig. 3 is an illustrated cross section view showing another embodiment of the present invention. In this embodiment, a hollow portion 16a of a dielectric resonator element 16 is so formed that it has a cross-shaped cross section. That is, the hollow portion 16a of the dielectric resonator element 16 comprises four pieces of a cutout portion 17 with rectangular cross section. Fig. 4 is an illustrated cross section view showing a modification of the embodiment of Fig. 3. As compared with the embodiment of Fig. 3, in this embodiment, eight pieces of a cutout portion 17 with a rectangular cross section are formed which are extended radially in radius directions of a dielectric resonator element 16. As mentioned above, the shape or the number of the cutout portion 17 may be varied. In this case, the outer shape of the tuning unit 18 should be formed somewhat smaller than the inner shape of the hollow portion 16a of the dielectric resonator element 16. Further, in each embodiment mentioned above, the dielectric resonator is formed in a cylinder or a column shape and the dielectric resonator for TE 0lδ mode is provided. However, a dielectric resonator element or a case having a polygonal outer shape may be used. In this case, a resonator operation will be in TE 0lδ mode. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and giving example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: A dielectric resonator comprising: a case (12); a cylindrical hollow dielectric resonator element (16) fixed and held in said case (12) and having a hollow axial portion (16a); a unitary dieletric tuning unit (18) which is capable of being axially inserted into and withdrawn from said hollow axial portion (16a) of said dielectric resonator element (16), and has a cross sectional shape substantially matching the cross sectional shape of said hollow axial portion (16a) including cutout portions (17), said hollow axial portion (16a) having a cross sectional shape which is defined by a cylindrical portion which defines an inside diameter of said element, characterized by at least three radially directed cutout portions (17) which extend symmetrically from said cylindrical portion toward a periphery of said dielectric element (16), and whereby said cutout portions (17) extend radially outward from said cylindrical portion more than half way to said periphery and thereby extending to a region of maximum electrical field intensity within said dielectric resonator element (16). Dielectric resonator in accordance with claim 1, wherein the cross sectional shape of the dielectric tuning unit (18) is substantially the same as but smaller than the cross sectional shape of said hollow axial portion including that cutout portions (17). Dielectric resonator in accordance with claim 1 or 2, wherein said resonator element (16) has two ends, and said cutout portions (17) extend substantially between said two ends. Dielectric resonator in accordance with any preceding claim, wherein each said cutout portion (17) is formed with a cross section which is at least partially rectangular. Dielectric resonator in accordance with any of the claims 1 to 3, wherein each said cutout portion (17) is formed with a cross section which is at least partially U-shaped. Dielectric resonator in accordance with any preceding claim, wherein there are four radially directed cutout portions (17) which define substantially equal angles there between. Dielectric resonator in accordance with any of claims 1 to 5, wherein there are six radially directed cutout portions (17) which define substantially equal angles between. Dielectric resonator in accordance with any preceding claim, wherein distal ends of said cutout portions (17) furthest toward the periphery of said resonator element (16) are rectangular in cross section. Dielectric resonator in accordance with any of claim 1 to 7, wherein distal ends of said cutout portions furthest toward said periphery of said resonator element (16) are round in cross section. Dielectric resonator in accordance with any preceding claim, comprising input and output means (24a, 24b, 26a, 26b) on said case (12) for the input and output of electromagnetc energy.

Inventors: ARAKAWA SHIGEJI MURATA MANUFAC, ISHAKAWA YOUHEI MURATA MANUFAC, KUNIOKA SHINICHI MURATA MANUFA, TAKEHARA KOUICHI MURATA MANUFA, TANIZAKI TORU MURATA MANUFACTU, WADA HIDEKAZU MURATA MANUFACTU, ARAKAWA, SHIGEJI MURATA MANUFACTURING CO.,LTD., ISHAKAWA, YOUHEI MURATA MANUFACTURING CO.,LTD., KUNIOKA, SHINICHI MURATA MANUFACTURING CO.,LTD., TAKEHARA, KOUICHI MURATA MANUFACTURING CO.,LTD., TANIZAKI, TORU MURATA MANUFACTURING CO.,LTD., WADA, HIDEKAZU MURATA MANUFACTURING CO.,LTD.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1988
Main classification: H01P7
IPC codes: H01P7