Coaxial resonator and dielectric filter using the same

Details Coaxial resonator and dielectric filter using the same Coaxial resonator and dielectric filter using the same

1998-09-22

2001-02-20

Lee, Benny (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S206000, C333S222000

Reexamination Certificate

active

06191668

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a coaxial resonator used as a filter in a microwave band and a dielectric filter constructed using the coaxial resonator.
2. Description of the Prior Art
As microwave remote communication has been put into practice, there has been a demand for a communication equipment that is more lightweight and smaller in size; thereby, leading to a demand to miniaturize a duplexer which is an essential component in such an equipment.
Examples of a filter used for a duplexer in a microwave band generally includes a so-called coaxial resonator constituted by an outer conductor provided on an outer peripheral surface of a dielectric member having a through hole provided therein and an inner conductor provided on an inner peripheral surface of the through hole, and a strip-line type resonator using a strip line. As filters, a quarter-wavelength type filter which resonates at one-fourth of a wavelength at a resonance frequency f by producing the filter in one side short-circuited construction has been generally well known. In addition, a coaxial dielectric resonator constructed using a material having a high dielectric constant (∈r=40 to 90) has been widely used as one suitable for miniaturization.
Particularly in a portable telephone, a receiving band and a transmission band are used proximate to each other. Accordingly, a so-called polarized method having an attenuation pole is adopted for a filter for a duplexer. Examples of such a polarized method include a method of obtaining an anti-resonance frequency by connecting a capacitor or an inductor in series with a coaxial dielectric resonator (see Japanese Utility Model Laid-Open Gazette No. 4566/1987) and a method of coupling resonators which are not adjacent to each other (see Japanese Patent Laid-Open Gazette No. 108801/1988).
FIGS. 24A and 24B
illustrate a polarized filter explaining the former method, where
FIG. 24A
is a perspective view showing the filter, and
FIG. 24B
is a diagram showing an equivalent circuit thereof. Three coaxial resonators are used to fabricate a polarized band-pass filter. In this polarized band-pass filter, three coaxial resonators
62
are provided on a dielectric substrate
61
(see, FIG.
24
A). Antiresonance capacitances
63
a
,
63
b
and
63
c
(see,
FIG. 24B
) are respectively connected to the coaxial resonators
62
. In addition, chip capacitors
64
a
to
64
d
are provided on the dielectric substrate
61
. The two chip capacitors
64
b
and
64
c
out of the chip capacitors
64
a
to
64
d
are inter-stage coupling capacitors for coupling the coaxial resonators to each other.
However, in the above described filter shown in
FIG. 24A and 24B
, an inter-stage coupling portion is required. Accordingly, the dielectric substrate
61
must be made relatively large so as to form the inter-stage coupling portion, thereby to making it impossible to miniaturize the filter. On the other hand, in the above described method of coupling the resonators which are not adjacent to each other, a jump coupling substrate is required, thereby similarly making it impossible to miniaturize the filter.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above described circumstances and has for its object to provide a small-sized dielectric filter and to provide a coaxial resonator used for the small-sized dielectric filter.
In a quarter-wavelength type coaxial resonator in which an outer conductor is formed on an outer peripheral surface of a dielectric block having at least four side surfaces and having a through hole provided in its approximately central part and an inner conductor is formed on an inner peripheral surface of the through hole, and one of two end faces perpendicular to the through hole is opened and the other end face is short-circuited, a coaxial resonator according to the present invention is characterized in that a pair of an input electrode and an output electrode which are not brought into electrical contact with the outer conductor and are independent of each other is provided in a position in proximity to the opened end face on the outer peripheral surface of the dielectric block, and respective portions of both the electrodes are extended to the side surfaces which are respectively adjacent to the electrodes.
According to the present invention, the input electrode and the output electrode are capacitively coupled to each other, and the input electrode and the output electrode are respectively capacitively coupled to the inner conductor. Coupling capacitances can be adjusted depending on the areas of the above described electrodes. Coaxial resonators can be connected to each other by electrode portions extended to the above described side surfaces (extended portions).
Furthermore, the dielectric filter according to the present invention is characterized in that a plurality of coaxial resonators as described above are arranged side by side, the above described input and output electrodes formed in the respective coaxial resonators are positioned on the same plane, the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the extended portion of the input electrode and the extended portion of the output electrode respectively formed in the adjacent coaxial resonators are brought into close contact with each other.
Consequently, the necessity of using a dielectric substrate for carrying chip capacitors and the like in constructing the dielectric filter as a polarized filter is eliminated, thereby making it possible to miniaturize the dielectric filter.
Furthermore, in a quarter-wavelength type coaxial resonator in which an outer conductor is formed on an outer peripheral surface of a dielectric block having at least four side surfaces and having a through hole provided in its approximately central part and an inner conductor is formed on an inner peripheral surface of the through hole, and one of two end faces perpendicular to the through hole is opened and the other end face is short-circuited, a coaxial resonator according to the present invention is characterized in that an independent conductor for capacitance is provided so as not to be brought into electrical contact with the outer conductor in a position in proximity to the opened end face on the outer peripheral surface of the dielectric block, or an independent conductor for induction is provided so as to be brought into electrical contact with the inner conductor through a conductor on the short-circuited end face and so as not to be brought into electrical contact with the outer conductor in a position in proximity to the short-circuited end face on the outer peripheral surface of the dielectric block.
According to the present invention, the above described coaxial resonator comprises the conductor for capacitance or the conductor for induction on the outer peripheral surface of the dielectric block. The conductor for capacitance or the conductor for induction provides a place where in coupling the coaxial resonators to each other by reactance constituted by a chip component, the chip component is carried.
Furthermore, a dielectric filter according to the present invention is characterized in that a plurality of coaxial resonators each comprising the above described conductor for capacitance are used, all or a part of the conductors for capacitance formed in the respective coaxial resonators are positioned on the same plane, the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the conductors for capacitance in the adjacent coaxial resonators are coupled to each other by reactance, or a plurality of coaxial resonators comprising the above described conductor for induction are used, all or a part of the conductors for induction formed in the respective coaxial resonators are positioned on the same plane, and the opened end faces and the short-circuited end face

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