Dielectric filter having resonators arranged in series

Details Dielectric filter having resonators arranged in series Dielectric filter having resonators arranged in series

1999-12-30

2001-12-04

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S202000, C333S134000

Reexamination Certificate

active

06326867

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a dielectric filter which may be surface-mounted upon a substrate such as a printed circuit board and, more particularly, to a dielectric band-pass filter having resonators arranged in series for passing a specific frequency band of signals in radio communication transceiver.
DESCRIPTION OF THE PRIOR ART
Hereafter, various embodiments of conventional dielectric filters will be described schematically, referring to
FIGS. 1 and 2
.
The
FIG. 1
is a perspective view showing an embodiment of the conventional dielectric filter having three resonators in single dielectric block.
The conventional dielectric filter shown in
FIG. 1
includes a hexahedral dielectric block
101
, which is coated with conductive material except the top surface and, a first, second and third resonators
102
a
,
102
b
and
102
c
vertically formed within the dielectric block
101
.
Each of the resonators
102
a
,
102
b
and
102
c
is formed by a hole vertically through the dielectric block
101
and coated with conductive metal. Each of the resonators
102
a
,
102
b
and
102
c
functions as a short-circuited ¼ wavelength resonator.
Also, the conventional filter has two additional holes
103
, which are positioned between the adjacent two resonators respectively, for adjusting a coupling magnitude between the resonators
102
a
,
102
b
and
102
c
. In this case, the holes
103
are not coated with the conductive metal.
Further, the conventional filter has conductive rods
104
a
and
104
b
inserted into the first and third resonators
102
a
and
102
c
and connected to input and output terminals respectively. In this case, a dielectric substance
105
a
is inserted between the first resonator
102
a
and the conductive rod
104
a
, and a dielectric substance
105
b
is inserted between the third resonator
102
c
and the conductive rod
104
b
. Each of the dielectric substances
105
a
and
105
b
couples the input and output terminals to the first and third resonators
102
a
and
102
c.
In the conventional filter constructed as above-described, a signal transmitted from the input terminal is transferred to the first resonator
102
a
by an electromagnetic coupling between the first resonator
102
a
and the conductive rod
104
a
. Then, the signal in the first resonator
102
a
is transmitted to the second resonator
102
b
by electromagnetic coupling between the first and second resonators
102
a
and
102
b
and, continuously, to the third resonator
102
c
by an electromagnetic coupling between the second and third resonators
102
b
and
102
c
. Thereafter, the signal is transferred to the conductive rod
104
b
by the electromagnetic field coupling between the conductive rod
104
b
and the third resonator
102
c.
In this case, the coupling magnitude between resonators may be adjusted by changing the size of the holes
103
or by displacing the position of the holes
103
in forward or backward of the dielectric block
101
. Also, the number of the resonators may be increased so that a high attenuation characteristic can be achieved in the stop band.
However, the conventional dielectric filter as above-described has a plurality of problems as follows:
1) Since an additional process is required in order to prevent the holes from being coated with the conductive metal, the manufacturing cost of the conventional filter is high;
2) The signal transmitted into the filter may be transmitted to undesired position through opened surface (i.e., the top surface of the dielectric); and
3) When the number of the resonators is increased in order to achieve a high attenuation characteristic, an insert loss is increased and physical dimension of the filter is large.
The
FIG. 2
is a perspective view showing another embodiment of the conventional dielectric filter having two resonators within a single dielectric block.
The conventional dielectric filter shown in
FIG. 2
includes a dielectric block
201
, two U-shaped resonators
202
and
203
vertically formed within the dielectric block
201
, and an input and output terminals
204
and
205
disposed on side surface of the dielectric block
201
. The two resonators
202
and
203
are positioned in parallel to longitudinal axis A-A′ of the dielectric block
201
and to each other. That is, the two resonators
202
and
203
are arranged in a row.
The bottom surface of the dielectric block
201
consists of a coated portion
206
coated with a conductive material and a non-coated portion
207
. Therefore, the U-shaped resonators
202
and
203
respectively have short-circuited portions
202
b
and
203
b
short-circuited to a ground plane, opened portions
202
c
and
203
c
, and coupling portions
202
a
and
203
a
for electrically connecting each of the short-circuited portions
202
b
and
203
b
to each of the opened portions
202
c
and
203
c
. At this time, each of the resonators
202
and
203
has a length corresponding to ¼ wavelength. In this case, the input and output terminals
204
and
205
are positioned adjacent to the non-coated portion
207
of the dielectric block
201
.
However, the conventional filter may be miniaturized by decreasing the volume, but there is a problem that the height mounted on a printed circuit board is higher because the resonators are arranged in a row.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a dielectric filter having resonators capable of decreasing the mounted height and improving an attenuation characteristic in a stop band.
In accordance with an aspect of the present invention, there is provided a dielectric filter having resonators arranged in series, comprising: a dielectric block; and a plurality of resonators formed within the dielectric block, each of the resonators having a first and second through holes formed vertically through the dielectric block and arranged in series along longitudinal axis of the dielectric block and a coupling portion electrically connecting an end of the first through hole to an end of the second through hole.


REFERENCES:
patent: 4733208 (1988-03-01), Ishikawa et al.
patent: 5208565 (1993-05-01), Sogo et al.
patent: 5396201 (1995-03-01), Ishizaki et al.
patent: 5929721 (1999-07-01), Munn et al.
patent: 6133808 (2000-10-01), Akakawa
patent: 62-213301 A (1987-09-01), None
patent: 404302503 A (1992-10-01), None
patent: 406006109 A (1994-01-01), None
Sagawa, et al.; Miniaturized Antenna Duplexers for Portable Radio telephone Terminals; 1990; pp. 417-420.
Ishizaki, et al.; A Stepped Impedance Comb-Line Filter Fabricated by Using Ceramic Lamination Technique; Apr. 1994.
Matsumoto, et al.; A Miniaturized Dielectric Monoblock Band-Pass Filter for 80 MHz Band Cordless telephone System; Apr. 1994; pp. 249-252.

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