Dielectric filter device

Abstract: A dielectric filter device including a stripline filter (10) having a plurality of strip-shaped resonance conductors (13,14) on its upper surface, and a plurality of dielectric blocks (20) each having a groove (21) coated with conductive layer (22) on the stripline filter, wherein the height of the arrangement can be reduced as compared with any conventional block type filter devices, and can be given a higher Q value than stripline filter devices.

Description: BACKGROUND OF THE INVENTION The present invention relates to a dielectric filter device having a stripline filter and dielectric blocks. Fig. 1 discloses a dielectric filter device in a prior art wherein it comprises a plurality of juxtaposed dielectric coaxial resonators each of which includes a rectangular parallelepiped dielectric block A. Each dielectric block A is provided with a through hole B having a circular cross section and extended in the center axial direction, and an external conductive layer C on an outer surface except a front surface thereof. The through hole B in the each dielectric block A has inner surface coated with a conductive layer D. An example of such a filter arrangement is disclosed in Japanese Patent Kokai No. 3-136502. Such a conventional filter arrangement has a disadvantage that it has larger in height because each of the juxtaposed dielectric coaxial resonators comprises the rectangular parallelepiped dielectric block. Therefore, it does not substantially meet a requirement for a size reduction of portable communication equipments such as portable telephones incorporating such a filter device. On the other hand, as a filter device for use with such portable communication equipments there is also known a stripline filter in which resonator conductors are arranged on a dielectric substrate. The stripline filter permits a reduction in thickness but shows a low Q value and thus a large insertion loss is to be involved. A dielectric filter comprising both a plurality of juxtaposed dielectric coaxial resonators and a stripline filter arranged on a dielectric substrate is described in US-A-4,703,291. However, in the arrangement described, the dielectric resonators are mounted on the substrate in such a way as to increase the thickness of the resulting filter still further. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a dielectric filter device capable of overcoming the problems or disadvantages of the conventional filter arrangements. According to the present invention, there is provided a dielectric filter device comprising a stripline filter and a plurality of dielectric blocks, the stripline filter comprising a thin dielectric substrate having an outer surface, the dielectric substrate being provided with a plurality of resonance conductors on a first portion of the outer surface and a first ground conductor on a substantial portion of the remainder of the outer surface other than said first surface portion, the resonance conductors being arranged to form a predetermined pattern and each having one end connected to said first ground conductor, the plurality of dielectric blocks each being thicker than the dielectric substrate and each having a respective outer surface, each block being provided with an open groove on a first portion of the outer surface, a second ground conductor on a substantial portion of the remainder of the outer surface other than said first surface portion, and a conductive layer formed on said first surface portion, the dielectric blocks being mounted with respect to the stripline filter such that the first portion of the outer surface of the dielectric substrate is in confronting relationship with the first portion of the outer surface of the dielectric blocks and so that each dielectric block is positioned on a respective resonance conductor of the stripline filter with the conductive layer connected to said respective resonance conductor. Also in the dielectric filter device of the present invention, a spacer may be additionally provided between adjacent dielectric blocks mounted on the stripline filter for adjusting the magnetic coupling therebetween. By connecting the resonance conductors of the stripline filter located on both the outermost sides thereof to input and output terminals, respectively, an electrical coupling occurs between the inner conductive layers of the adjacent dielectric blocks and between the resonance conductors of the stripline filter, thereby performing a filteration of a required frequency bandwidth. The dielectric filter device of the present invention can be made thinner than the conventional arrangement with dielectric blocks but can be given a desired resonator Q value by changing the dielectric blocks in thickness. The present invention will now be described by way of example with reference to the accompanying drawings: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view showing a conventional dielectric block filter device; Fig. 2 is a partially exploded perspective view of a dielectric filter device embodying the present invention; Fig. 3 is a schematic front view showing the dielectric filter device of Fig. 2 when being assembled; and Fig. 4 is a schematic front view showing modifications of the dielectric filter device embodying the present invention. DETAILED DESCRIPTION Referring to Figs. 2 and 3, there is shown a dielectric filter device according to an embodiment of the present invention, which comprises a stripline filter 10 and two dielectric blocks 20. The stripline filter 10 includes a thin dielectric substrate 11 made of titanium oxide dielectric ceramic material, and has a thickness thinner than that of the dielectric blocks 20 as shown in Fig. 3. A ground conductor 12 is formed on the substantial portion of the outer surface of the substrate 11 which is exposed to the atmosphere when being assembled except the front surface thereof. A plurality of (two in the illustrated arrangement) Strip-shaped resonance conductors 13 and 14 are formed on the upper surface of the substrate 11 so as to form a predetermined pattern. Rear ends of the resonance conductors 13 and 14 are connected with the ground conductor 12 to form short-circuit terminals, while front ends of the the resonance conductors 13 and 14 are terminated at the same level as the front edge of the substrate to form open-circuit terminals. Also on the upper surface of the dielectric substrate 11 edge conductors 15 are partially formed along the lateral edge portion thereof and an intermediate conductor 16 is formed between the resonance conductors 13 and 14 in parallel therewith. The edge conductors 15 and the intermediate conductor 16 connected with the ground conductor 12. Alternately, the intermediate conductor 16 may be formed partly or may be omitted. As will be seen, each of the resonance conductors 13 and 14 has a lateral extension 17 electrically connected with an input and output terminals (only one is shown by reference numeral 18) which are provided on the the lateral outer surfaces of the substrate 11, are electrically separated from the ground conductor 12, and are connected with external conducting wires (not shown). Similarly, each of the dielectric blocks 20 is made of titanium oxide dielectric ceramic material, and is of a rectangular parallelepiped. Each dielectric block 20 is formed with a downwardly open groove 21 of a semicircular cross section which is extended along the longitudinal direction thereof. The groove 21 has an inner surface formed with an inner conductive layer 22 which is extended to the edge portions of the groove 21 as shown by 23 in Figs. 2 and 3. Also, each dielectric block 20 is formed with a ground conductor 24 on the upper and lateral surfaces except the front and bottom surfaces thereof. Along the lateral and rear edge portions of the bottom surface of each dielectric block 20 there are formed edge conductors 25 which are connected with the ground conductor 24. As will be seen in Fig. 2, each of the lateral surfaces of the dielectric blocks 20 which are opposite to each other is formed with a conductor 26 only on the peripheral edge portion thereof. The conductor 26 is connected with the ground conductor 24. The dielectric blocks 20 are mounted on the strip-shaped resonance conductors 13 and 14 of the stripline filter 10, and each of the inner conductive layers 22 in the dielectric blocks 20 is electrically connected with the corresponding resonance conductor 13 or 14 via the edge conductive conductor portions 23. Then a spacer frame 27 is interposed between the dielectric blocks 20 for forming a gap therebetween. The spacer frame 27 is used for adjusting the magnetic coupling between the adjacent dielectric blocks 20. That is, if the degree or quantity of the coupling between the resonance conductors 13 and 14 is stronger, their resonance bandwidth becomes too wide. By provision of the spacer frame 27 it is possible to reduce the degree of the coupling between the resonance conductors 13 and 14. Similar adjustment is possible even by providing a dielectric layer having a smaller dielectric constant than that of the dielectric blocks 20 instead of the spacer frame 27, or by forming an edge conductor connected with the ground conductor 24 on the lateral surfaces adjacent to each other of the dielectric blocks 20. When the dielectric blocks 20 are mounted on the stripline filter 10, the input and output terminals 18 on both sides or lateral surfaces of the stripline filter 10 are electrically connected with the inner conductive layers 22 through the strip-shaped resonance conductors 13 and 14, respectively. Therefore, between the inner conductive layers 22 of the adjacent dielectric blocks 20 and between the strip-shaped resonance conductors 13 and 14 there are obtained electrical couplings which result in a filtering of the desired frequency bandwidth. With the illustrated embodiment, the input and output terminals 18 are provided on the stripline filter 10 for the external connection. However, for this end, a connecting terminals may be inserted into the grooves 21 of the dielectric blocks 20. In that case, the coupling capacitance may be changed by adjusting the insertion depth of the connecting terminals into the grooves. Furthermore, the dielectric filter may be constructed by providing more than three strip-shaped resonance conductors on the dielectric substrate and the same number of dielectric blocks which are mounted on the substrate. The present invention may be carried out as a comb type arrangement in which the open-circuit or short-circuit ends of the respective resonance conductors are aligned with each other, or an interdigital type arrangement in which the respective resonance conductors are alternately directed. With the illustrated filter device, the dielectric blocks may be modified as shown in Fig. 4. In an arrangement illustrated in (a) each dielectric block is made thinner and is provided with a shallow groove. In the case of (b) each dielectric block is provided with a deep groove. As described above, with the provision of a plurality of dielectric blocks each having a groove coated with conductive layer and a stripline filter having a plurality of strip-shaped resonance conductors on its upper surface, the height of the arrangement can be reduced as compared with any conventional block type filter devices. Therefore, the described embodiment can provide a dielectric filter device which fully meets with the requirement for smaller and thinner dimensions of the portable communication equipment. Also, the provision of a plurality of dielectric blocks each having a groove coated with conductive layer on the stripline filter can be given a higher Q value than stripline filter devices.

Claims: A dielectric filter device comprising a stripline filter (10) and a plurality of dielectric blocks (20), the stripline filter (10) comprising a thin dielectric substrate (11) having an outer surface, the dielectric substrate (11) being provided with a plurality of resonance conductors (13, 14) on a first portion of the outer surface and a first ground conductor (12) on a substantial portion of the remainder of the outer surface other than said first surface portion, the resonance conductors (13, 14) being arranged to form a predetermined pattern and each having one end connected to said first ground conductor (12), the plurality of dielectric blocks (20) each being thicker than the dielectric substrate (11) and each having a respective outer surface, each block (20) being provided with an open groove (21) on a first portion of the outer surface, a second ground conductor (24) on a substantial portion of the remainder of the outer surface other than said first surface portion, and a conductive layer (22) formed on said first surface portion, the dielectric blocks (20) being mounted with respect to the stripline filter (10) such that the first portion of the outer surface of the dielectric substrate (11) is in confronting relationship with the first portion of the outer surface of the dielectric blocks (20) and so that each dielectric block (20) is positioned on a respective resonance conductor (13, 14) of the stripline filter (10) with the conductive layer (22) connected to said respective resonance conductor (13, 14). A dielectric filter device as claimed in claim 1, wherein said stripline filter (10) is provided with an intermediate conductor (16) which is arranged between adjacent resonance conductors (13, 14), extends parallel thereto and is connected to the ground conductors (24) of adjacent dielectric blocks (20). A dielectric filter device as claimed in claim 1 or claim 2 and comprising a spacer (27) provided between adjacent dielectric blocks (20) and mounted on said stripline filter (10) for adjusting the magnetic coupling therebetween. A dielectric filter device as claimed in claim 3, wherein said spacer (27) comprises a frame made of dielectric material which is interposed between opposed surfaces of the adjacent dielectric blocks (20). A dielectric filter device as claimed in claim 3, wherein said spacer (27) comprises a dielectric layer which is formed on opposing surfaces of the adjacent dielectric blocks (20).

Inventors: ITO KENJI, SHIMIZO HIROYUKI, ITO, KENJI, SHIMIZU, HIROYUKI, ITO, KENJI, C/O NGK SPARK PLUG CO., LTD., Shimizo, Hiroyuki, c/o NGK Spark Plug Co., Ltd.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD.
Application year: 1993
Main classification: H01P1
IPC codes: H01P7, H01P1