Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-12-10
2001-10-16
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S207000
Reexamination Certificate
active
06304159
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric filter including a plurality of juxtaposed dielectric ceramic resonators, and a method of adjusting its frequency bandwidth.
2. Related Background Art
There have been proposed various dielectric filters comprising a dielectric ceramic block including a plurality of juxtaposed resonators. In the dielectric ceramic block a plurality of through holes are provided in juxtaposed configuration. Each of the through holes is formed with an inner conductor on its inner wall. The dielectric ceramic block has an outer conductor provided on the outer surface portions thereof except an open circuit end surface portion at which one end of each through hole meets.
One example of such conventional dielectric filters is shown in
FIG. 1
of the accompanying drawings. The illustrated filter A comprises a dielectric ceramic block B including two resonators C
1
and C
2
therein. An outer conductor D is provided on the outer surface portions of the block B except an open circuit end surface portion E and input/output terminal pads F are provided on one lateral surface portion of the block B provided with the outer conductor D and are electrically separated from the outer conductor by peripheral gaps. On the open circuit end surface portion E a transverse strip conductor G is provided for separating the resonators C
1
and C
2
from each other. The strip conductor G has both ends connected to the outer conductor D. This strip conductor G is operative to provide polarization on a high band side. The electromagnetic coupling between the resonators C
1
and C
2
can be regulated by modifying the configuration and/or width of the strip conductor G.
Recently, with the spread of digital communication system such as mobile phone it is required to use a dielectric filter having a wider frequency band. However, with the conventional filter mentioned above, the provision of the transverse strip conductor on the open-circuit end surface of the block is operative to provide polarization on a high band side, but the frequency bandwidth is reduced. Meanwhile, the use of dielectric filter having a narrow frequency band is required for some applications. However, the dielectric filter having the arrangement mentioned above can not be adjusted to have a desired frequency band in accordance with the requirement for an application.
SUMMARY OF THE INVENTION
In view of these circumstances, it is therefore an object of the present invention to provide a dielectric filter in which a bandwidth may be modified, and method of adjusting the bandwidth thereof.
According to one aspect of the invention, there is provided
a dielectric filter comprising;
a dielectric ceramic block having a first and second end surfaces, a first and second lateral side surfaces opposite to each other, and a third and fourth lateral side surfaces to each other;
a plurality of juxtaposed resonators each resonator including a through hole provided within the block to be extended from the first end surface to the second end surface of the block and an inner conductor layer provided on an inner wall surface of the through hole;
an outer conductor layer provided on outer surface portions of the block with exception of said first end surface;
input/output pads provided on the first lateral side surface of the block at respective positions close to the first end surface and opposite to the associated resonators, each pad being capacitively coupled with the associated resonator;
a strip conductor member provided transversely between the adjacent through holes on said first end surface of the block, the strip conductor member having one end connected to the outer conductor layer on one of the first and second lateral side surfaces of the block, and other end formed as an open circuit end; and
a non-conductive region defined between the open circuit end of the strip conductor member and the outer conductor layer on the other of the first and second lateral side surface.
In one embodiment of the invention, one end of the strip conductor member may be connected to the outer conductor layer on the first lateral side surface of the block where the input/output pads are positioned. In this case the non-conductive region may be defined between the open circuit end of the strip conductor member and the outer conductor layer on the second lateral side surface opposite to the first lateral side surface.
Alternately, one end of the strip conductor member may be formed as an open circuit, and the other end may be connected to the outer conductor layer on the second lateral side surface of the block where no input/output pad is positioned. In this case, the non-conductive region is defined between the open circuit end of the strip conductor member and the outer conductor layer on the first lateral side surface of the block.
According to another aspect of the invention, there is provided a method of adjusting the frequency bandwidth of a dielectric filter comprising a dielectric ceramic block having a first and second end surfaces, and a first and second lateral side surfaces opposite to each other, a plurality of juxtaposed resonators each resonator including a through hole provided within the block to be extended from the first end surface to the second end surface of the block and an inner conductor layer provided on an inner wall surface of the through hole, an outer conductor layer provided on outer surface portions of the block with exception of said first end surface, and input/output pads provided on the first lateral side surface of the block at respective positions close to said first end surface and opposite to the associated resonators, each pad being capacitively coupled with the associated resonator, wherein the method comprises the steps of:
forming a strip conductor member transversely between the adjacent through holes on said first end surface of the block so that one end of the strip conductor member is connected to the outer conductor layer on one of the first and second lateral side surfaces of the block, and other end is separated from the other lateral side surface to form an open circuit end, whereby defining a non-conductive region between the open circuit end of the strip conductor member and the outer conductor layer on the other lateral side surface; and
setting a width or space of the non-conductive region or insulation gap whereby adjusting the frequency bandwidth.
In the testing of a frequency characteristic it has been found that the dielectric filter thus arranged has a frequency characteristic in which 3 dB frequency bandwidth is wider than that of the conventional arrangement such as one illustrated in FIG.
1
. The wording “3 dB frequency bandwidth” means a frequency bandwidth at a range below 3 dB from the minimum value of an insertion loss in the band.
FIG. 2A
illustrates one measured example of a frequency characteristic (a) and a reflected wave characteristic (b) of the conventional dielectric filter having a strip conductor member arranged as shown in FIG.
1
. The used dielectric filter includes input/output pads provided on the lateral side surface of a dielectric ceramic block at respective positions close to an open circuit end surface of the block and opposite to the associated resonators so that each pad is capacitively coupled with the associated resonator.
After measuring of the frequency characteristic in this dielectric filter, the dielectric filter was modified as follows. The transverse strip conductor member was removed at one end thereof connected to the outer conductor layer on the lateral side surface of the block where no input/output pad is positioned as in the present invention. A non-conductive region was defined between the one open end of the strip conductor member and the outer conductor layer. This modified dielectric filter has a frequency characteristic (a) and a reflected wave characteristic (b) as shown in FIG.
2
B. It will be seen in
FIG. 2B
that the frequency characteristic (a) has a flattened
Funahashi Masahiro
Murakami Katsuhisa
Ono Shoji
Larson & Taylor PLC
NGK Spark Plug Co. Ltd.
Nguyen Patricia T.
Pascal Robert
LandOfFree
Dielectric filter with adjustable frequency bandwidth does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dielectric filter with adjustable frequency bandwidth, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric filter with adjustable frequency bandwidth will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2612113