Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-04-06
2001-05-22
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219100, C333S134000
Reexamination Certificate
active
06236291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter for use in a microwave range or a millimeter wave range and also to a duplexer and a communication device using such a dielectric filter.
2. Description of the Related Art
There is an increasing need for a high-capacity and high-speed communication system. To meet such a need, the communication frequency band is being expanded from the microwave band to the millimeter wave band. In particular, the submillimeter wave band is attractive for various applications such as a wireless LAN, a portable video telephone, and a next-generation satellite broadcasting system. As the frequency band expands, a filter is required which is small in size, inexpensive, and suitable for use in a planar circuit. In view of the above, the inventors of the present invention have proposed a “submillimeter wave band-pass filter using a planar-circuit dielectric resonator” (Proceedings of Conference of the Institute of Electronics, Information, and Communications Engineers, 1996, C-121).
The structure of this dielectric filter is shown in an exploded perspective fashion in FIG.
8
. In
FIG. 8
, reference numeral
3
denotes a dielectric plate having electrodes formed on its respective two principal surfaces wherein each electrode is partially removed so as to form non-electrode areas. The non-electrode areas of each electrode are formed at locations corresponding to those of the opposite electrode. In
FIG. 8
, reference numeral
1
denotes an electrode formed on a surface, on the upper side in
FIG. 8
, of the dielectric plate
3
, and reference numerals
4
a
,
4
b
, and
4
c
denote non-electrode areas. Reference numerals
6
and
7
denote a substrate and a frame, respectively. Both the substrate
6
and the frame
7
are made of ceramic. An electrode is formed on the lower surface of the substrate. An electrode is also formed in the peripheral area
11
, outside the frame
7
, of the upper surface of the substrate. Furthermore, an electrode is formed on the external side faces of the frame
7
. Reference numeral
8
denotes a cover also made of ceramic wherein an electrode is formed on its surface in contact with the electrode
1
and an electrode is also formed on the side faces of the cover. Microstrip lines
9
and
10
serving as probes and also as input/output terminals are formed on the upper surface of the substrate
6
.
In the above-described structure, parts of the dielectric plate
3
located between the respective two opposing non-electrode areas serve as TE010-mode dielectric resonators wherein adjacent dielectric resonators are coupled with each other and each resonator is also coupled with the microstrip line
9
or
10
.
Because the conventional dielectric filter shown in
FIG. 8
has a structure in which the dielectric plate
3
including the dielectric resonators is located between the frame
7
and the cover
8
, when the frame
7
is soldered to the substrate
6
to form a single unit, the resultant unit has a warp due to the difference between the linear expansion coefficient of the frame
7
and that of the substrate
6
. The dielectric plate
3
having a modulus of elasticity similar to those of the frame
7
and the cover
8
is bonded together with the cover
8
to the upper side of the warped frame
7
via a conductive adhesive. Thus, after these elements are combined together, a stress occurs due to the difference in linear expansion coefficient between the frame
7
and the cover
8
and also due to the warping of the frame
7
. The stress can cause the frame
7
or the cover
8
to be separated from the dielectric plate
8
. The stress can also cause the dielectric plate
3
to have a crack. Even when the dielectric plate does not encounter separation or crack in normal environments, the stress can cause a reduction in environmental resistance.
Although the rigidity of the frame
7
can be increased by increasing the wall thickness of the frame
7
, the result is an increase in the overall size. On the other hand, if the height the frame
7
is increased, the result is an increase in the distance between the probes and the corresponding resonators, which makes it impossible to obtain desired external coupling. As a result it becomes impossible to achieve desired characteristics.
In view of the above, it is an object of the present invention to provide a dielectric filter no longer having the above-described problems. It is another object of the invention to provide a duplexer and a communication device using such a dielectric filter.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a dielectric filter including a case, a dielectric plate, and a cover. The case has a supporting part for supporting one surface of the dielectric plate and a side wall surrounding the side faces of the dielectric plate wherein the supporting part and the side wall are formed in an integral fashion. The cover is placed on the case such that the opening of the case is closed with the cover thereby forming a part of a cavity. In this structure, the stress between the dielectric plate and the case is suppressed.
By forming the supporting part for supporting the dielectric plate including the dielectric resonator and the side wall surrounding the side faces of the dielectric plate in the integral fashion as described above, it becomes possible to increase the rigidity of the case thereby ensuring that the case has a warp to a reduced degree when the case is bonded to the substrate. As a result, the dielectric plate has less stress in a part where the dielectric plate is supported. Furthermore, because the dielectric plate is supported by the supporting part of the case in such a manner that only one surface of the dielectric plate is in contact with the supporting part, the dielectric plate has less stress due to the difference of the linear expansion coefficient of the dielectric plate from that of the case or the cover than will occur in a structure in which both the upper and lower surfaces of the dielectric plate are in contact with the case and cover, respectively, as in the conventional technique.
In the present invention, the supporting part of the case for supporting the dielectric plate preferably includes a recess for preventing a corner of the dielectric plate from being in contact with the supporting part. As opposed to the conventional structure in which the stress due to the difference in the linear expansion coefficient is most concentrate in the corners of the dielectric plate, the structure according to the invention allows the corner of the dielectric plate to have a reduced stress. As a result, the stress is also reduced over the entire region of the dielectric plate.
Furthermore, in the present invention, a corner of the dielectric plate is preferably cut off or rounded so that the stress in the corner of the dielectric plate is deconcentrated.
The present invention also provides a duplexer including a transmitting filter, a receiving filter, transmission signal input port, an input/output port, and a reception signal output port, wherein either one of or both of the transmitting and receiving filters are realized using a dielectric filter according to any of aspects of the invention, and wherein the transmitting filter is disposed between the transmission signal input port and the input/output port, and the receiving filter is disposed between the reception signal output port and the input/output port.
According to the present invention, it is possible to achieve high rigidity without having to increase the thickness of the side wall surrounding the side faces of the dielectric plate and thus it becomes possible to realize a small-sized dielectric filter and also a small-sized duplexer.
The invention also provides a communication device including the above-described duplexer, a transmitting circuit, and a receiving circuit, wherein the transmitting circuit is connected to the transmission signal input port of the duplexer and t
Hiratsuka Toshiro
Kanagawa Kiyoshi
Sonoda Tomiya
Murata Manufacturing Co. Ltd.
Nguyen Patricia T.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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