Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1994-05-31
1996-02-06
Lee, Benny
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333204, 333219, H01D 120
Patent
active
054898811
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a filter employed in mobile communication apparatuses such as cordless telephones, portable telephones and the like as well as a method of manufacturing the same.
BACKGROUND ART
A structure of this type of filter known heretofore (e.g. from JP-A-03-71710) is shown in FIG. 13 and FIG. 14. In FIG. 13, numerals 70 to 76 denote green sheets of a dielectric material, wherein the green sheets 71 and 72 are provided with electrodes 77, 78, 79, 80 for capacitors. On the other hand, the green sheet 74 is provided with electrodes 81 and 82 for coils, while the green sheet 76 is provided with shielding electrodes 83 and 84. The green sheets 70-76 shown in FIG. 13 are laminated and subsequently fired at such a temperature at which the electrodes 77-84 (e.g. of silver or copper) do not make disappearance, whereby these sheets are integrated in such a structure as shown in FIG. 14. In FIG. 14, numerals 85 and 86 denote input/output terminals. Thus, in the filter known heretofore, capacitors are formed by the electrodes 77-80 disposed in opposition, while coils are formed by the electrodes 81 and 82, wherein the filter is constituted by these capacitors and coils.
A problem of the prior art filter described above is seen in that satisfactory filter characteristics can not be obtained because no-loaded Q of a resonator comprising the capacitor and the coil can not be made high. More specifically, referring to FIG. 13, since the green sheets 70 to 76 are allowed to be fired only at a temperature at which the electrodes 77-84 can not disappear, significant dielectric loss is incurred, as a result of which a constant indicating low loss of the resonator (no-loaded Q) assumes a small value. Consequently, the filter comprising the resonators each having low unloaded Q suffers significant insertion loss in the pass-band with the characteristic in the attenuation band being damped. Thus, it is impossible to use the filter in such applications in which the requirement for the characteristic requirement is severe.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to prevent the filter characteristics from degradation by increasing no-loaded Q of the resonator.
For achieving the above object, there is proposed according to the present invention a filter, which comprises a substrate having first and second strip lines formed on a top surface and mutually coupled through an electromagnetic field and an earth pattern on a bottom surface, respectively, a dielectric layer laminated on the top surface of the substrate and having capacitor patterns formed on a top surface thereof in opposition to the aforementioned first and second strip lines, and a cap fitted over and above the dielectric layer and having an electrically conductive surface at least at one of top and bottom surfaces, and an electrically conductive film formed on a portion of an outer peripheral surface of the aforementioned substrate and connected to the earth pattern on the bottom surface, wherein at least a portion of an outer periphery of the cap is led downwardly toward the electrically conductive film so that the portion led downwardly and the electrically conductive film are connected together.
With the structure described above, because the cap is fitted over the dielectric layer with a space therebetween, the electric fields from the first and second strips concentrate in the direction toward the substrate. In this conjunction, as the substrate, there can be used such one which has previously been fired independently at a high temperature. Thus, the dielectric loss can be minimized, as a result of which the unloaded Q of the resonator formed by the first and second strip lines can be made extremely high, whereby the filter characteristics can be protected against degradation.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of a filter according to a first exemplary embodiment of the present invention as viewed from top surface of the filter, FIG. 2 is a perspective v
REFERENCES:
patent: 4281301 (1981-07-01), Stegens
patent: 4703392 (1987-10-01), Robertson
patent: 4975664 (1990-12-01), Ito et al.
patent: 5248949 (1993-09-01), Eguchi et al.
patent: 5373271 (1994-12-01), Hirai et al.
patent: 5374909 (1994-12-01), Hirai et al.
Himori Thuyoshi
Ieda Tomoaki
Ishikawa Takayoshi
Takahashi Hiroshi
Yuda Naoki
Gambino Darius
Lee Benny
Matsushita Electric - Industrial Co., Ltd.
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