Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-02-24
2004-08-10
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S202000, C333S219100
Reexamination Certificate
active
06774744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency filter, and more particularly to a dielectric filter, a dielectric duplexer, and a communication device, which are used in a base station of a microwave band communication system.
2. Description of the Related Art
A first example of a conventional dielectric filter will be described with reference to FIG.
1
.
The dielectric filter
110
is constituted of two dielectric resonators
120
a,
120
b
arranged in parallel, and metallic panels
111
a,
111
b
for covering the opening parts of the dielectric resonators
120
a,
120
b.
Each of the dielectric resonators
120
a,
120
b
is constituted of a rectangular-prism-shaped cavity
121
made of a dielectric ceramic, and a dielectric block
122
disposed within the cavity
121
. A conductive layer
123
is formed by painting and baking a silver paste on an outside surface of the cavity
121
. The dielectric block
122
has a cross-shape in which two dielectric poles are intersected. Typically, the cavity
121
and the cross-shaped dielectric resonator
122
are integrally molded. Coupling loops
112
a,
112
b
are mounted to the metallic panel
111
a.
One end of each loop is connected to a central conductor of a coaxial connector
113
a,
113
b
mounted to the metallic panel
111
a,
and the other end thereof is grounded by being connected to the metallic panel
111
a.
Further, a coupling loop
112
c
for electromagnetic-coupling the two dielectric resonators
120
a,
120
b
is mounted to the other metallic panel
111
b.
When a signal is inputted from an outside, a magnetic field is generated in the area surrounding the loop
112
a,
and the generated magnetic field couples to a magnetic field surrounding one of the dielectric poles in the dielectric block
122
. Further, an electromagnetic field around the one of the dielectric poles and an electromagnetic field around the other one of the dielectric poles that is perpendicular thereto are coupled by a groove
125
formed at the intersection of the two dielectric poles of the dielectric block
122
. For the other dielectric resonator
120
b,
a similar chain of electromagnetic field couplings occurs, and as a result, the dielectric filter
110
functions as a fourth order band pass filter.
The loop
112
a
is constituted of a first part
112
a
1
that extends in a direction that is the same as a length direction of one of the dielectric poles, and a second part
112
a
2
that extends in a direction perpendicular to the first part
112
a
1
. The loop
112
b
has a similar structure. Consequently, the first part
112
a
1
of the loop
112
a
couples to one of the dielectric poles extending in the same direction of the dielectric block
122
, and at the same time the second part
112
a
2
of the loop
112
a
couples to the other one of the dielectric poles in the dielectric block
122
. As such, it is possible to provide an attenuation pole on either a low frequency side or a high frequency side of the resonant frequency of the dielectric resonator, by electromagnetic-coupling the loop
112
a
to the first and second resonators formed by the respective dielectric poles in the dielectric resonator
120
a
simultaneously.
In general, for a signal with a frequency lower than a resonant frequency, its phase will not change even when passing through a resonator, but for a signal with a frequency higher than the resonant frequency, its phase will change by &pgr; when passing through the resonator. For example, when coupling to an in-phase resonant mode that occurs in one of the dielectric poles corresponding to the first part
112
a
1
of the loop
112
a,
and coupling to a reversed-phase resonant mode that occurs in the other one of the dielectric poles corresponding to the second part
112
a
2
of the loop
112
a,
an attenuation pole is generated on the low frequency side of the resonant frequency similarly.
A second example of a conventional dielectric filter will be described with reference to FIG.
2
.
FIG. 2
is a perspective view of a dielectric filter according to a second conventional example. Moreover, the identical symbols are attached to the same parts as in the previous conventional example, and it will be illustrated by showing only the dielectric resonator that constitutes the dielectric filter.
In the conventional dielectric resonator
120
c
shown in
FIG. 2
, dent parts
124
are formed in an outside of the cavity
121
extending toward an inside thereof, at the four points where the cross-shaped dielectric resonator
122
joins the cavity
121
. As a result, the dielectric resonator
120
c
has three resonant modes, i.e., TM
110
mode, TM
111
mode, and TM
110
mode at respective parts thereof, similar to those shown in the electric field distribution diagram of
FIG. 4
, and the dielectric filter functions as a three-stage band pass filter.
Because several spurious modes are generated outside the pass band, it is necessary in a dielectric filter used in a communication base station, and the like, to provide attenuation poles both on the low frequency side and on the high frequency side of the pass band in order to restrain them. However, in the dielectric filter in the first conventional example, with the dielectric resonator having two resonant modes, and the loop providing input/output (I/O) coupling for these two resonant modes simultaneously, an attenuation pole can be provided on either the low frequency side or the high frequency side, but not both. Accordingly, in order to provide the attenuation poles both on the high frequency side and on the low frequency side, it is necessary to arrange one additional dielectric resonator in parallel, in order to provide the attenuation pole on the other side. That is, in the first conventional example, for providing the attenuation poles on the low frequency side and on the high frequency side, two dielectric resonators are always required, and thus there is a problem of increasing the size of the dielectric filter.
Further, in the dielectric filter in the second conventional example, there is no way to provide attenuation poles on both the low side and the high side of the resonant frequency band.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a dielectric filter, which solves these problems, which provides attenuation poles on the low frequency side and on the high frequency side of the resonant frequency, and which is capable of being miniaturized.
These and other objects of the present invention can be achieved by a dielectric filter according to a first aspect of the invention, including a dielectric resonator having at least three resonant modes, and configured including a conductive cavity, and a dielectric resonator arranged within the cavity, and an input/output coupling unit that couples to the dielectric resonator, wherein the input/output coupling unit couples to a resonant mode at the first stage, as well as to at least one resonant mode at the h-th stage (h=2n+1: where n is an integer) approximately in negative-phase with respect to the first stage, among the resonant modes of the dielectric resonator.
The objects of the present invention can also be achieved by a dielectric filter according to a second aspect of the invention, including a dielectric resonator having at least three resonant modes, and configured including a conductive cavity, and a dielectric resonator arranged within the cavity and an input/output coupling unit that couples to the dielectric resonator, wherein the input/output coupling unit couples to a resonant mode at the last stage, as well as to at least one resonant mode at the (k−2n)-th stage (where n is an integer), the last stage being the k-th stage, approximately in negative-phase with respect to the last stage, among the resonant modes of the dielectric resonator.
In the dielectric filter according to the foregoing first and second aspects of the invention, preferably the input/output coupling unit is a loop havi
Hattori Jun
Kubo Hiroyuki
Kubota Kazuhiko
Murata Manufacturing Co. Ltd.
Nguyen Patricia T.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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