Wave transmission lines and networks – Resonators – Dielectric type
Reexamination Certificate
2000-04-06
2003-06-03
Nguyen, Patricia T. (Department: 2817)
Wave transmission lines and networks
Resonators
Dielectric type
C333S134000, C333S202000
Reexamination Certificate
active
06573812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dielectric filters, duplexers, and communication devices incorporating the same, which are used in base stations having high-frequency communication apparatus.
2. Description of the Related Art
A conventional dielectric filter
110
will be illustrated with reference to
FIGS. 11 and 12
.
FIG. 11
is a side view of the conventional dielectric filter
110
, and
FIG. 12
is a plan view thereof. In these figures, shield cases are cut away to show the inside of the filter
110
.
As shown in
FIGS. 11 and 12
, the conventional dielectric filter
110
comprises a cylindrical dielectric resonator
111
, a supporting base
112
for supporting the dielectric resonator
111
, and a metal shield case
113
for containing the dielectric resonator
111
and the supporting base
112
. In addition, a loop
115
as an input coupling unit and a probe
116
as an output coupling unit are attached to the shield case
113
such that the loop
115
and the probe
116
, respectively, are coupled to the dielectric resonator
111
.
In this arrangement, the loop
115
is formed by connecting an end of a metal line or a metal plate to the shield case
113
to be grounded, and connecting the other end thereof, for example, to the central conductor of a coaxial connector so as to perform a magnetic-field coupling with the dielectric resonator
111
. In general, a loop has a structure in which one end of the loop is connected to a shield case, and the other end thereof is connected to a central conductor to retain both ends of the loop. This structure permits filter characteristics to be stabilized, since the position of the loop does not change due to influence from the outside, and the amount of coupling can be maintained constant.
Meanwhile, regarding the probe, an electric-field coupling is performed between the probe and a dielectric resonator by making an end of a metal line open, and connecting the other end thereof, for example, to the central conductor of a coaxial connector. In the electric-field coupling between the probe and the dielectric resonator, the amount of coupling with the dielectric resonator is larger than the amount of coupling between a dielectric resonator and a loop having the same length as that of the probe.
In the conventional dielectric filter
110
having such a structure, a signal is inputted from the loop
115
as the input coupling unit so as to couple the loop
115
with the TE
01
&dgr; mode of the dielectric resonator
111
. After this, the dielectric resonator
111
and the probe
116
as the output coupling unit are coupled so as to output only the signals of a specified frequency band.
As an input coupling unit and an output coupling unit, besides the combination of a loop and a probe, the combination of only loops, and the combination of only probes are conventionally known.
Next, referring to
FIGS. 13 and 14
, a description will be given of a multi-mode dielectric filter proposed by the assignee of the present application in Japanese Patent Application No. 10-220371 which was not laid-open to the public at the time of the priority date of this application. Thus, the disclosures of the drawings as well as the contents of the Japanese application do not constitute prior art.
FIG. 13
is a side view of the multi-mode dielectric filter denoted by reference numeral
120
, and
FIG. 14
is a plan view thereof. In each of these figures, a shield case is cut away to show the inside of the filter.
As shown in
FIGS. 13 and 14
, the multi-mode dielectric filter
120
comprises a dielectric resonator
121
, a supporting base
112
for supporting the dielectric resonator
121
, and a metal shield case
113
containing the dielectric resonator
121
and the supporting base
112
. In addition, a loop
125
a
as an input coupling unit and another loop
125
b
as an output coupling unit are attached to the shield case
113
so that the loops
125
a
and
125
b
are respectively coupled with the dielectric resonator
121
.
The dielectric resonator
121
has a configuration seen as if it were formed by cutting away four corners of a square when observed from above. With this configuration, the dielectric resonator
121
can be used as a triple-mode dielectric resonator, which resonates in three resonant modes shown in
FIG. 5
, such as the TM
01
&dgr;
x+y
mode, the TE
01
&dgr;
Z
mode, and the TM
01
&dgr;
x−y
mode. In this case, each of the subscripts x, y, and z indicates each of the directions of x, y, and z set as an axial direction. For example, the TM
01
&dgr;
x+y
mode is equivalent to the TM
01
&dgr; mode obtained when the sum of a vector x and a vector y is set as the axial direction. The axis z indicates upper and lower directions, and the electric field is indicated by a solid line, whereas the magnetic field is indicated by a broken line.
In the multi-mode dielectric resonator
120
having such a structure, the loop
125
a
as the input coupling unit is positioned in a direction perpendicular to the magnetic field of the TM
01
&dgr;
x+y
mode so as to couple the loop
125
a
and the TM
01
&dgr;
x+y
mode of the dielectric resonator
121
. Then, the TM
01
&dgr;
x+y
mode and the TE
01
&dgr;
Z
mode are coupled, and furthermore, the TE
01
&dgr;
Z
mode and the TM
01
&dgr;
x−y
mode are coupled. Lastly, the TM
01
&dgr;
x−y
mode of the dielectric resonator
121
is coupled with the loop
125
b
as the output coupling unit positioned in a direction perpendicular to the magnetic field of the TM
01
&dgr;
x−y
mode. This structure permits the multi-mode dielectric filter
120
to serve as a three-stage band pass filter.
In the conventional dielectric filter, both the input coupling unit and the output coupling unit are positioned on the upper side of the dielectric resonator. In this case, the positions of the input coupling unit and the output coupling unit are determined by considering the amount of coupling between the input coupling unit and the dielectric resonator, and the amount of coupling between the output coupling unit and the dielectric resonator.
However, as shown above, when the input coupling unit and the output coupling unit are relatively close to each other, a relatively great mutual influence is generated between the input coupling unit and the output coupling unit. Therefore, when the positions for arranging both the input coupling unit and the output coupling unit are determined, it is necessary to consider the mutual influence generated between the coupling units. This makes designing of the filter difficult. Similarly, this problem often occurs in a case in which an input coupling unit and an output coupling unit are disposed on the side positions of the dielectric resonator.
In contrast, in the multi-mode dielectric filter proposed in Japanese Patent Application No. 10-220371, the two resonant modes orthogonal to each other are coupled to the input coupling unit and the output coupling unit. As a result, in order not to make the input coupling unit and the output coupling unit mutually intersect in a space-limited structure, it is necessary to reduce the lengths of both the input coupling unit and the output coupling unit.
Meanwhile, in order to increase the amount of coupling between the dielectric resonator and the input coupling unit, and the amount of coupling between the dielectric resonator and the output coupling unit, it is necessary to increase the lengths of the input coupling unit and the output coupling unit. However, in such a dielectric filter, due to a space limitation in the structure, the lengths of the input coupling unit and the output coupling unit must be reduced. Furthermore, the loops are used as the input coupling unit and the output coupling unit. Thus, no great amount of coupling can be obtained. In other words, in the multi-mode dielectric filter proposed in Japanese Patent Application No. 10-220371, in addition to the above problem, when filter characteristics with a broad
Abe Shin
Ise Tomoyuki
Kubota Kazuhiko
Wakamatsu Hiroki
Dickenstein Shapiro Morin & Oshinsky LLP
Murata Manufacturing Co. Ltd
Nguyen Patricia T.
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