Dielectric filter

Details Dielectric filter Dielectric filter

1998-12-11

2001-01-02

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S207000, C333S223000, C333S134000

Utility Patent

active

06169464

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter. Particularly, the present invention relates to a dielectric filter in which an open area without being spread with a conductive material is formed on the rear face of a dielectric block with a conductive material spread thereon, thereby making it possible to improve the filtering characteristics of the filter and to miniaturize the filter.
2. Description of the Prior Art
Recently, the mobile communication system using the radio frequency (RF) band is replacing the wired communication system. Accordingly, the demand for the mobile communication apparatuses is being greatly increased, and studies on them are being briskly carried out. The special feature of the mobile communication system is that the user carries the terminal anywhere. Therefore, it is required that the performance of the mobile communication apparatus has to be improved, and that a miniaturization and light weight have to be achieved.
As described above, in order to simultaneously achieve the improvement of the performance and the compactness and light weight, every component of the mobile communication apparatus has to be miniaturized. For this purpose, a unitized dielectric filter is widely used. Generally, in the dielectric filter, there are connected a plurality of dielectric blocks with a coaxial resonator provided on each of them, thereby obtaining the desired pass band characteristics of the RF band. In the unitized dielectric filter, a plurality of coaxial resonators are formed to a single dielectric block, thereby obtaining the pass band characteristics. This unitized dielectric filter is provided at both the receiving part and the transmitting part, so that the transmitted and received radio waves can be filtered. The required pass band is about 20-30 MHz.
FIG. 1
is a perspective view of the conventional unitized dielectric filter. As shown in the drawing, the dielectric filter includes: a first face
5
and a second face
7
oppositely facing from each other; and a hexahedral dielectric block
1
having side faces between the first and second faces
5
and
7
. Within the dielectric block
1
, there are a plurality of resonance holes
3
disposed in parallel with each other and passing through the first and second faces
5
and
7
. The side faces which lie between the first and second faces
5
and
7
are coated with a conductive material to form a ground electrode. The first face
5
of the dielectric block
1
forms an open area not coated with a conductive material. Further, the insides of the resonance holes
3
are coated with a conductive material to form internal electrodes.
Around each of the resonance holes
3
of the first face
5
, there is formed a conductor pattern
8
having a certain width. The conductor pattern
8
is connected to the internal electrode of the resonance hole
3
to form a loading capacitance and a coupling capacitance. The resonance frequency of the resonator is decided by the resonance hole
3
and by the loading capacitance, while the coupling capacitance couples the two resonators together. Further, the side faces which lie between the first face
5
and the second face
7
are provided with input/output terminals
12
a
and
12
b.
In the above described filter, the filtering characteristics become different in accordance with the coupling capacitance and the resonance frequency of the resonator which are decided by the loading capacitance and the resonance hole
3
. Therefore, the filtering characteristics are decided by the size of the conductor pattern
8
which forms the loading capacitance and the coupling capacitance. The loading capacitance is dominantly decided by the distance between the side face of the dielectric block
1
and the conductor pattern
8
of the first face
5
. Therefore, in order to adjust the filtering characteristics of the unitized dielectric filter, the gap between the ground electrode and the conductor pattern
8
and the gap between the adjacent conductor patterns
8
have to be adjusted by adjusting the size of the conductor pattern
8
.
However, the size of the mobile communication apparatus has to be reduced to the minimum for its carrying convenience. Therefore, the dielectric filter also have to be miniaturized as far as possible. For this, the bulk of the dielectric block
1
has to be reduced. In order to reduce the bulk, the distance between the resonance holes
3
and between the holes
3
and the side face has to be reduced, but this means that the area of the first face
5
has to be reduced.
Therefore, the conductor pattern
8
of the first face
5
has to be reduced. If the size of the conductor pattern
8
is reduced, it is difficult to manufacture the filter having the required filtering characteristics. Further, in order to miniaturize the dielectric filter, the gap between the conductor patterns
8
has to be reduced. Generally, the ground electrode and the conductor pattern
8
of the first face
5
are formed by a screen printing process. This screen printing process shows an error range of 25-30 &mgr;m in its line width. Therefore, in the case where the conductor patterns
8
are formed around two resonance holes
3
to form a miniaturized filter, the reduction of the size of the conductor pattern
8
and of the gap between the conductor pattern
8
and the ground electrode encounters a limit, and therefore, the desired magnitude of the loading capacitance cannot be achieved. Further, in the case where the gap between the conductor patterns
8
is made small by the reduction of the area of the first face
5
, the conductor patterns
8
can be short-circuited due to the errors of the screen printing process.
FIG. 2
is a perspective view showing a duplex dielectric filter for filtering the transceiving signals of the mobile communication apparatus. Like the unitized dielectric filter, the duplex dielectric filter includes: first and second faces
5
and
7
; and a hexahedral dielectric block
1
having side faces between the first and second faces
5
and
7
. Within the dielectric block
1
, there are a plurality of resonance holes
3
disposed in parallel with each other and passing through the first and second faces
5
and
7
. On the second face
7
and the side faces, there are coated ground electrodes (not shown in the drawing). Further, an internal electrode is formed on the inside of the resonance hole
3
so as to form a resonator. Further, an open area is formed on the second face
7
, without being coated with a conductive material.
Around each of the resonance holes
3
of the first face
5
, there is formed a conductor pattern
8
having a certain width. A loading capacitance is formed between the ground electrode and the conductor pattern
8
, while a coupling capacitance is formed between the conductor patterns of the adjacent resonance holes
3
. Further, the first face
5
is provided with an antenna terminal
13
and reception and transmission terminals
12
a
and
12
b.
In the duplex dielectric filter of the drawing, the three resonance holes of the left part of the first face
5
are receiving ends for receiving RF signals from the external, while the four resonance holes of the right part are transmitting ends for transmitting RF signals to the outside. Under this condition, the respective resonance holes
3
form resonators and form the loading capacitances.
Generally, in the duplex dielectric filter, the RF band of the transmitting terminals is lower than the RF band of the receiving terminals. Therefore, an electric field effect is dominant between the resonance holes
3
of the receiving terminals, while a magnetic field effect is dominant between the resonance holes
3
of the transmitting terminals. Therefore, the resonators of the receiving terminals form a capacitance coupling, while the resonators of the transmitting terminals form an inductance coupling.
In the duplex dielectric filter like in the dielectric filter of
FIG. 1
, the coupling between the resonators and the

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