Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
1999-06-11
2001-05-22
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S206000, C333S204000
Reexamination Certificate
active
06236290
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a multilayer filter having characteristics of a band pass filter for use in mobile communication equipment such as a portable cellular telephone and the like.
A typical conventional multilayer filter comprises a plurality of strip-line resonators in the form of a multilayer body which is generally formed from dielectric and conductive layers which are stacked up by a sheeting or screen printing method before being sintered. In order to reduce the size of the multilayer filter using the strip-line resonators, the resonance frequency is lowered by providing capacitors connected in parallel in the multilayer body to obtain target filter characteristics.
In such a multilayer filter as formed with the strip-line resonators, however, current is concentrated on the edge portion of the strip-line conductive layer and the Q-factor is degraded, which poses a problem in that good filter characteristics are unobtainable.
It has been proposed by JP-A 9-35936 to use through-hole electrodes as inductance elements for solving the foregoing problems.
The multilayer filter disclosed in the aforesaid Japanese Patent Publication is seemingly intended to set the ratio W/d of the diameter d of a through-hole to the width W of a multilayer body is set at about 13. With an arrangement like this, however, the Q-factor would never be improved because the resistance value grows larger, though a large inductance value can be secured.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multilayer filter using through-holes as inductance elements, in which the multilayer filter is small in size and capable of improving the Q-value further.
According to the present invention, a multilayer filter comprises a multilayer body formed by stacking and sintering dielectric and conductive layers; input-output terminal electrodes overlaid in both respective edge faces of the multilayer body; ground electrodes overlaid on both respective sides of the multilayer body; inductance elements in a form of a plurality of through-hole electrodes formed in the multilayer body; paralleled capacitors connected to the inductance elements formed in the multilayer body; and in that one end of each inductance element is electrically coupled to the input-output terminal electrode, the other end is connected to the conductive layer as a sealed electrode; and the ratio W/d of the diameter d of the through-hole electrode to width W between the ground electrodes on both edge faces of the multilayer body is set at not less than 1.6 and not greater than 11.4.
The multilayer filter according to the present invention is thus of quasi-coaxial type, that is, provided with the sealed electrodes in both respective sides of a body of generally cubic shape, and the through-hole electrodes as inductance elements. Moreover, not lower than about 70% of the maximum value is made obtainable as the Q-factor by setting the ratio of the diameter d of the through-hole to the width W of the multilayer body at the range of 1.6 to 11.4.
Further, in a multilayer filter, an impedance-matching capacitor is provided between the input-output terminal electrode and the inductance element.
REFERENCES:
patent: 5777533 (1998-07-01), Kato et al.
patent: 5783978 (1998-07-01), Noguchi et al.
patent: 6061227 (2000-06-01), Nogi
patent: 2303495 (1997-02-01), None
patent: 9-35936 (1997-02-01), None
Abe Toshiyuki
Ishitobi Norimasa
Jones Stephen E.
Lee Benny
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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