Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2002-08-29
2004-02-24
Wamsley, Patrick (Department: 2819)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S134000
Reexamination Certificate
active
06696905
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to dielectric filter devices for determining the frequency band pass characteristics to be used in mobile communications devices or the like.
BACKGROUND OF THE INVENTION
It is generally known that monoblock-type dielectric filters are used in mobile communications devices for transmitting and receiving signals, for example, in the frequency band of hundreds of megahertz to several gigahertz. Mobile communications devices, such as portable telephones, in recent years are adapted to serve a multiplicity of functions and made more compact and lightweight, and many monoblock-type dielectric duplexers are singly adapted to process different transmission and receiving frequencies for use in such devices (for example, Japanese Patent No. 3205337).
An example of duplexer which is such a conventional dielectric filter of the monoblock type will be described with reference to
FIG. 5. A
dielectric block
10
, for example, of a ceramic material or the like has hollow bores
40
to
44
,
49
,
50
. Electrically conductive layers are formed on the outer peripheral side surface
20
of the block and the upper surface thereof around the openings of the bores as indicated at
33
to
39
. Further provided on the upper surface are a first electrode
30
, second electrode
31
and third electrode
32
which are separate from these conductive layers.
As shown in
FIG. 5
, the bores
40
,
41
are arranged between the first electrode
30
and the second electrode
31
. The bore
49
is positioned between the second electrode
31
and the peripheral side surface. The bores
42
to
44
are arranged between the first electrode
30
and the third electrode
32
. The bore
50
is positioned between the third electrode
32
and the peripheral side surface
20
. The first electrode
30
is connected to an antenna (not shown), the second electrode
31
to a transmitter, and the third electrode
32
to a receiver.
A band-pass filter for the desired transmission frequency band is provided by suitably adjusting the dimensions and shapes (e.g., the diameter and depth of bores, and distance between conductive layers) of the bores
40
,
41
between the first and second electrodes
30
,
31
and the conductive layers
33
,
34
in the vicinity of openings of these bores. A trap having an attenuation pole at the desired frequency in the vicinity of the above-mentioned transmission frequency band can be provided by suitably adjusting the dimensions and shapes of the bore
49
between the second electrode
31
and the conductive layer on the peripheral side surface
20
and the conductive layer
38
in the vicinity of opening of the bore
Similarly, a predetermined band-pass filter for the receiving frequency band is provided by suitably adjusting the dimensions and shapes of the bores
42
to
44
between the first and third electrodes
30
,
32
and the conductive layers
35
to
37
in the vicinity of openings of these bores. A trap having an attenuation pole in the vicinity of the receiving frequency band can be provided by suitably adjusting the shapes of the bore
50
between the third electrode
32
and the conductive layer on the peripheral side surface and the conductive layer
39
in the vicinity of opening of the bore.
The dielectric duplexer described comprises two dielectric filters having two systems, i.e., transmitting system and receiving system, which use different frequencies. Since the filters are based on the same principles of the band-pass function and the trap function, these functions will be described with respect to the receiving system with reference to the filter characteristics diagrams of
FIGS. 7 and 8
.
FIG. 8
shows the characteristics of the band-pass filter which is capacitance-coupled by the bores provided between the first electrode and the third electrode and the conductive layers in the vicinity of these bores. The shapes of these bores and the conductive layers in the vicinity of the openings thereof are so adjusted as to provide the desired frequency pass band f
1
to f
2
. Ideally, it is desirable that the attenuation be as great as possible in the suppressing band outside the pass band, whereas in actuality, a sharp attenuation is not available at a frequency in the suppressing band near the pass band.
In communications devices, however, it is likely that a frequency near the pass band will also be used, for example, for processing signals in the receiver provided subsequent to the filter. In such a case, the receiving filter needs to have such attenuation characteristics that in the range of from the frequency f
2
at the pass-band limit to a frequency f
4
which is used for other signal transmission or receiving, the attenuation is at least a (dB) for example at a frequency of f
3
and at least b (dB) at the frequency f
4
. With reference to
FIG. 8
, the attenuation of the receiving filter is smaller than b (dB) at the frequency f
4
for other use, and there arises the problem that a sufficiently great S/N ratio is not available.
Accordingly with the conventional filter shown in
FIG. 5
, the bore
50
between the third electrode
32
and the conductive layer on the peripheral side surface and the conductive layer
39
near the opening of the bore are suitably adjusted in shape to thereby provide a trap having an attenuation pole, i.e., a great attenuation of c (dB), for example, in the vicinity of the frequency f
3
, and an attenuation of b (dB) also at a frequency over the frequency f
4
shown in FIG.
7
.
This method nevertheless requires an increased attenuation at f
3
, such that an attenuation occurs also near the frequency f
2
within the required pass band as indicated at d. The same is also true of the transmission side including the first and second electrodes
30
,
31
.
In the field of mobile communications devices such as portable telephones, it is required in recent years that the parts be made ever smaller. Since mobile phones need to be highly portable as an important feature of the commercial product and must therefore be smaller in size, it is not desirable to provide improved filter characteristics by adding new circuit components to the dielectric filter described.
SUMMARY OF THE INVENTION
To overcome the foregoing problems, the present invention provides a dielectric filter device comprising a dielectric block generally in the form of a rectangular parallelepiped and having a plurality of hollow bores formed therein and openings of the bores in an upper surface of the block, electrically conductive layers respectively covering a lower surface opposed to the upper surface, an outer peripheral side surface parallel to axes of the bores, inner peripheral surfaces defining the respective bores and the upper surface around the bore openings, and a plurality of electrodes separate from the conductive layers for connection to external devices. First bore opening portions are arranged between the first electrode formed on the upper surface or side surface of the block and the second electrode formed on the upper surface thereof to provide a filter for passing a predetermined frequency band, second bore opening portions being arranged between the second electrode and the side surface of the block.
In the dielectric filter device described, the second bore opening portions are preferably arranged perpendicular to the direction of arrangement of the first bore opening portions.
The invention described gives improved characteristics to the dielectric filter without providing external components on the filter.
REFERENCES:
patent: 5831495 (1998-11-01), Hino
patent: 3205337 (2001-06-01), None
patent: WO 93/24968 (1993-12-01), None
Ezaki Kenichi
Uchiyama Takaaki
Umeda Katsumi
Armstrong Kratz Quintos Hanson & Brooks, LLP
Sanyo Electric Co,. Ltd.
Wamsley Patrick
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