Dielectric filter having coaxial resonators and a notch pattern

Details Dielectric filter having coaxial resonators and a notch pattern Dielectric filter having coaxial resonators and a notch pattern

2001-07-11

2003-09-30

Tokar, Michael (Department: 2819)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S206000

Reexamination Certificate

active

06628180

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a dielectric filter having a plurality of quarter wavelength type coaxial resonators and, more particularly, to a dielectric filter having a notch pattern for improving an attenuation characteristic of a high frequency band.
2. Description of the Related Art
Dielectric filters have been used for attenuating side frequency bands of a desired frequency band. Typically, the dielectric filters, such as a ceramic filter, include a dielectric block, which is made of a ceramic material, and a plurality of coaxial resonators formed in the dielectric block. Both a minimum insertion loss for the desired frequency band and an attenuation ratio for a side band of the desired frequency band should be accomplished in the dielectric filter. Moreover, the dielectric filter used in a device having a high frequency-band needs a more improved attenuation characteristic for the high frequency band, which is supposed to pass the dielectric filter. However, it is impossible that these conventional dielectric filters are minimized to be installed in a reduced size device because of the existence of an additional volume for a separate and individual notch hole formed in the dielectric filter.
FIGS
1
A through
1
C show a conventional dielectric filter, an equivalent circuit of the dielectric filter of
FIG. 1A
, and a diagram showing a representative characteristic of the dielectric filter of
FIG. 1A. A
dielectric filter
10
shown in
FIG. 1A
includes a dielectric block having an upper surface, a lower surface spaced-apart from and being parallel to the upper surface, and four walls perpendicular to both the upper surface and the lower surface. A plurality of coaxial resonators
10
a
,
10
b
,
10
c
includes respective through holes
11
a
,
11
b
,
11
c
formed in the dielectric block. A through hole
11
d
for a separate and individual notch hole is formed in the dielectric block parallel to and adjacent to one of the outside coaxial resonators
10
a
,
10
c
in order to provide the attenuation characteristic to the high frequency pass band. Through holes
11
a
,
11
b
,
11
c
,
111
d
are arranged along between the lateral surfaces in a series from one of side surfaces to the other one of the side surfaces.
A conductive material is coated onto the lower surface, the side walls, and an peripheral portion of the upper surface.
Respective coated upper areas
11
-
1
,
11
-
2
,
11
-
3
,
11
-
4
as a loading capacitor pattern, coated with the conductive material are formed around the respective through holes
11
a
,
11
b
,
11
c
,
11
d
exposed on the upper surface of the dielectric block, and respective non-coated upper areas are formed between the coated peripheral portion of the upper surface and the coated upper areas of the resonators
10
a
,
10
b
,
10
c
and notch hole
10
d
.
An input pad
13
a
and an output pad
13
b
formed on one lateral side wall
22
a
are disposed adjacent to the upper surface to correspond to each of outside resonators. The input pad
13
a
and the output pad
13
b
are separated from the conductive material coated on the one lateral side wall
22
a
by non-coated lateral area
12
a
and non-coated lateral area
12
b
, respectively.
Non-coated lateral area
12
a
of lateral side wall
22
a
is coupled to non-coated upper area
14
a
of one of outside resonators
10
a
,
10
c
while the non-coated lateral area
12
b
of the one lateral side wall
22
a
is coupled to the non-coated upper area
14
c
of the other one of the outside resonators
10
a
,
10
b
,
10
c
,
10
d
.
An equivalent circuit of the dielectric filter of FIG
1
A is shown in FIG
1
B. In and out represent the input pad
13
a
and the output pad
13
b
. NR is defined by a diameter and a length of the notch hole. CN
1
is defined by a distance between the loading capacitor pattern and the input and output pads while CN
2
is defined by a distance between the loading capacitor pattern of the notch hole and the peripheral coated portion of the upper surface. FIG
1
C shows reflection loss S
11
and propagation characteristics or attenuation characteristics S
21
of dielectric filter
10
. An insertion loss P
1
of the high frequency band is formed, and an attenuation pole AP of the high frequency band is established.
The conventional dielectric filters, however, are prevented from being reduced in size because the dielectric filters must be provided with additional volume for the notch hole. The conventional dielectric filters are relatively bulky in size compared to the minimized device which is installed with the dielectric filter
10
. Therefore, I have found that the conventional dielectric filters are not reduced in size and that it is difficult and often inconvenient to install the conventional dielectric filter into the relatively small device in consideration of the recently developed minimized device.
SUMMARY OF THE INVENTION
It is an object to provide an improved dielectric filter having a plurality of resonators and input and output pads constructed according to the principles of the present invention.
It is another object to provide improved dielectric filter able to be reduced in size and to exhibit improved attenuation characteristics of a desired high frequency pass band.
It is yet another object to provide an improved dielectric filter able to remove a notch hole occupying an additional space in the dielectric filter.
It is still another object to provide an improved dielectric filter able to be mounted in a relatively small device which is installed with the dielectric filter.
It is a further object to provide an improved dielectric filter able to reduce a manufacturing cost.
It is also object to provide an improved dielectric filter able to shorten a manufacturing process.
These and other objects may be achieved by providing an improved dielectric filter having a notch pattern constructed according to the principles of the present invention. The dielectric filter includes a dielectric block, such as a dielectric ceramic block, defining an upper surface, a lower surface spaced apart from and being to the upper surface, two longitudinal lateral surfaces each spaced apart form each other and being parallel to both the upper surface and the lower surface, and two side surfaces disposed between the lateral surfaces and being perpendicular to the lateral surfaces. The lateral surfaces and the side surfaces form peripheral sides of the dielectric block between the upper surface and the lower surface. The lateral surfaces, the side surfaces, the lower surface, and a peripheral outside area of the upper surface are coated with a conductive material. Three resonators, such as first and second outside resonators and a middle resonator disposed between the outside resonators, includes through holes formed in the dielectric block, being parallel to each other, arranged between the lateral surfaces from one of the side surfaces toward the other one of the side surfaces in a series, and having respective openings exposed on the upper surface.
The conductive material is coated on each peripheral inner wall of the through holes. Also, the conductive material is coated around each opening of the through holes to form coated upper areas in order to provide a loading capacitance pattern to respective resonators. The coated upper areas are connected to the conductive material coated on the peripheral inner wall of the through holes. Non-coated upper area is formed around each of the coated upper areas of the resonators and between the peripheral outside area and each of the coated upper areas of the resonators.
Two non-coated lateral areas are formed on one of the lateral surfaces adjacent to the upper surface and coupled to the respective non-coated upper area of the upper surface. An input pad and an output pad are disposed within each of the non-coated lateral area of the lateral surface at a first position corresponding to the first resonator and a second position corresponding to the second resonat

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