Dielectric filters

Abstract: This invention is to offer a compact and high performance dielectric filter consisting of a quarter wavelength dielectric body (11) provided with a through-hole (12) between upper and lower surfaces of said dielectric body, electrodes (15,16) deposited on an external and lower surfaces of said dielectric body, and more than at least two independent electrodes (13,14) provided on internal surface of said through-hole, extending to upper and lower surfaces of said dielectric body. With this dielectric filter construction, said through-hole performs a role to construct plural quarter wavelength resonators and performs, at the same time, a role to adjust the coupling between said plural resonators, yielding a compact dielectric filter of simple construction.

Description: This invention relates to dielectric filters employed in high-frequency communication equipments, and is to offer compact dielectric filters of simple construction. BACKGROUND OF THE INVENTION A conventional dielectric filter is now explained by referring Fig. 4 which shows a pillar-shaped quarter-wavelength dielectric body 1 provided with plural through-holes (in this case, three holes) 2, 3 and 4 which connect upper and lower surfaces of said pillar-shaped dielectric body, electrodes 5 provided on outer and lower surfaces of said dielectric body 1, and pillar-shaped insulators 8 and 9 in which lead wires 6 and 7 are incorporated integrally inserted in said holes 2 and 4. With the above-explained construction of conventional resonator, two quarter-wavelength coaxial resonators are constructed by parts including said holes 2 and 4, and said hole 3 takes a role to adjust the magnetic field coupling between said two coaxial resonators. Lead wires 6 and 7 are capacitively coupled to electrodes coated on internal surfaces of said holes 2 and 4 through insulators 8 and 9, and lead in and out electric signals. According to the construction of such, three through-holes 2, 3, and 4 have to be provided within said dielectric body 1, and this means that (2n-1) holes have to be provided on said dielectric body in order to construct a filter having n-stages of resonators. However, this construction work requires a highly complicated and precise press molding of dielectric ceramics to prepare said dielectric body 1, and this process is nearly impossible to apply on a small dielectric body 1 because of close distances between holes 2, 3, and 4. Moreover, this process difficulty would be enhanced when a larger diameter hole 3 required to adjust coupling between resonators has to be provided, and this process is definitely disadvantageous to construct miniature dielectric filters. Moreover, since two independent insulators 8 and 9 have be consistently provided, this increases number of parts and difficulties of assembling works. SUMMARY OF THE INVENTION The present invention is to solve such problems associated with conventional dielectric filters, and to offer compact and high-performance dielectric filters. The technical means of the invention to solve the above-described problems include a provision of single through-hole between upper and lower surfaces of a pillar-shaped quarter wavelength resonator, provision of electrodes covering outer and lower surfaces of said dielectric body, and a provision of more than two independent electrodes on internal surfaces of said through-hole to cover spaces between said upper and lower surfaces within said through-hole. The invention is fully defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the nature, features and advantages of the present invention, provided below is a detailed description of a few preferred illustrative embodiments of the invention, which are illustrated by and best understood with references to the accompanying drawings wherein: Fig. 1(a) shows an perspective view of an embodiment of dielectric filter of the invention, and Fig. 1(b) shows a top view of cross-section of said dielectric filter shown in Fig. 1 sectioned at the X-X′ line. Fig. 2(a) shows a perspective view of dielectric filters of another embodiment of the invention, and Pig. 2(b) shows a cross-section of said dielectric filter shown in Fig. 2(a) sectioned at the Y-Y′ line. Fig. 3 show a perspective view of dielectric filter of still another embodiment of the invention, and Fig. 4 show a perspective view of conventional dielectric filter. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1(a) shows a perspective view of a dielectric filter of the invention, and Fig. 1(b) shows a top view of said dielectric filter sectioned at the X-X′ line shown in Fig. 1(a), wherein a pillar-shaped quarter wavelength dielectric body 11 equipped with upper and lower surfaces made on said ceramic dielectric body or other material, is equipped with an oblong through-hole 12. Two independent internal electrodes 13 and 14 are provided also on an internal surface of said through-hole 12, and these-electrodes extend to said upper and lower surfaces of said quarter wavelength dielectric body 11. Outer electrodes 15 and 16 are provided also on an outer surface and lower surface of said quarter wavelength dielectric body 11. Said electrodes 13, 14, 15, and 16 can be formed by an electroplating or metallizating processes. Since only respective ends of said internal electrodes 13 and 14 are electrically connected to said outer electrode 16 provided on said lower surface of said dielectric body 11, two quarter wavelength resonators of which internal conductors are made of said internal electrodes 13 and 14 are thus produced by this construction. A resonator having said internal conductor 13 as its internal conductor is named resonator A, and a resonator having said internal conductor 14 as its internal conductor is named resonator B for a convenience here. Said resonators A and B are magnetically coupled each other as shown in Fig. 1(b) constituting a double-stage dielectric filter. The dotted line and solid line in Fig. 1(b) show directions of electric field and magnetic field respectively. The cross-section of said hole 12 can be either one of circular, oblong, eyeglass-shaped, or cross-shaped holes, and the magnetic coupling between resonators A and B is variable according to the shape of hole 12. Since single oblong hole is easier to form from a view point of press-molding of ceramics, an employment of this simplifies the associated problems and structures of dielectric body. By inserting an insulator 21 incorporating lead terminals 19 and 20 into said hole 12 from the upper surface of said dielectric body 11, said leads terminals 19 and 20 are capacitively coupled to each of said internal electrodes 13 and 14 through said insulator 21, connections to the external circuit become possible The mechanical strength of said insulator 21 is considerably higher by taking a shape fitted into said through-hole 12 than that of conventional column shaped one, and thus, a number of components can be reduced also. Then, it is needless to say that any filter having multistage resonators can be constructed with single hole by taking an above-shown construction of resonator. In addition to the above, this requires no conventional holes to adjust the inter-stage coupling, and provides a better ceramic moldability, and this is particularly advantageous to construct miniaturized filters. Fig. 2(a) is to show another embodiment of dielectric filter of the invention, and Fig. 2(b) shows a top view of said filter sectioned at Y-Y′ line shown in Fig. 2(a). An oblong through-hole 32 having two column sections 33 and 34 is provide within a dielectric body 31 provided with upper and lower surfaces, and internal electrodes 35 and 36 extended toward an external surface and lower surface of said dielectric body 31 are provided on internal surfaces of said column sections 33 and 34 to constitute a double-stage dielectric filter such as the embodiment shown in Figs. 1(a) and 1(b). Furthermore, an insulator in which lead wires 39 and 40 are incorporated within and having an outer shape fitted into said oblong through-hole 32 is inserted into said through-hole 32 from the surface of said dielectric body 31, and it is integrated within said through-hole to construct a dielectric filter. Said dielectric filter having such a construction has not only features of the embodiment shown in Figs. 1(a) and 1(b), but Q of each resonator remains high because wider widths of said internal electrodes 35 and 36 constituting internal conductors of resonators can be provided. Furthermore, a higher mechanical strength of said insulator can be secured because of its particular shape, and said internal electrodes 35 and 36 provided onto said column shaped parts 33 and 34 can be easily metallized by transfer printing by using a round roller. If a lower coupling between resonators of dielectric body of such construction is desired, it can be accomplished by providing a cross-shaped hole at a portion other than said internal electrodes 35 and 36 provided within said through-hole 32. The resonator stages can also be increased easily by increasing the number of said column shaped parts within said through-hole 32 by a number of desired stages. Still another embodiment of dielectric filter of the invention is shown in Fig. 3 wherein a through-hole 43 is provided within a pillar-shaped dielectric body 42 having upper and lower surfaces, and two independent internal electrodes 44 and 45 extending to said upper and lower surface are provided. Electrodes are provided also on an external surface and lower surface of said dielectric body 42. An inter-stage electrode 46 to alter the coupling between said internal electrodes 44 and 45 is provided at a position between two said internal electrodes 44 and 45. Said coupling can be altered by the position and dimensions of said inter-stage electrode 46. In addition to this, input and output electrodes 47 and 48 are provided on the upper surface of said dielectric body 42 in order to capacitively couple said internal electrodes 44 and 45 each other. According to the construction of dielectric filter of the invention, a multistage filter can be realized by means of simple molding process, and advantages shown in the following can be realized easily. (1) A multistage filter of simple construction can be constructed by providing single through-hole in a dielectric body. (2) A molding process is simple because only a through-hole has to be provided, and said through-hole providing internal electrodes can also be used as a hole to adjust the coupling between resonators. (3) This filter construction is advantageous particularly to construct a filter on a miniaturized dielectric body. (4) A higher mechanical strength can be secured because only one insulator incorporating lead terminals has to be used, and its outer shape fitted to said through-hole provided in said dielectric body is integrated with said through-hole.

Claims: A dielectric filter comprised of a pillar-shaped quarter wavelength dielectric body (11) having a through-hole (12) between upper and lower surfaces of said dielectric body (11) provided with electrodes on the external and lower surfaces (15, 16) of said dielectric body (11), and characterised in that at least two independent electrodes (13, 14) on internal surfaces of said through-hole (12), extending to upper and lower surfaces of said quarter wavelength dielectric body. A dielectric filter according to Claim 1 wherein said through-hole (32) is provided with at least two column shaped through-hole parts (32, 35, 36) (fig. 2). A dielectric filter according to Claims 1 or 2 wherein an insulator (21) incorporating more than at least two independent lead wires (19, 20) within and having an external shape fitted to said through-hole provided in said quarter wavelength dielectric body (11) is integrated within said through-hole (fig 1). A dielectric filter according to Claims 1 or 2 wherein an electrode (46) to adjust coupling between isolated electrodes (44, 45) provided within said through-hole is provided on said quarter wavelength dielectric body (fig 3). A dielectric filter according to Claims 1 or 2 wherein electrodes (47, 48) which are capacitively coupled to electrodes within said through-hole (43), are provided on an upper surface of said quarter wavelength dielectric body in order to input and output electric signals (fig 3).

Inventors: AIZAWA KIMIO, FUJINO TAKASHI, ISHIZAKI TOSHIO, AIZAWA, KIMIO, FUJINO, TAKASHI, ISHIZAKI, TOSHIO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01P1
IPC codes: H01P1, H01P5