Stacked dielectric filter

Details Stacked dielectric filter Stacked dielectric filter

2002-06-27

2004-12-07

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S025000, C333S026000, C333S185000

Reexamination Certificate

active

06828881

ABSTRACT:

This application claims the benefit of Japanese Application 2001-201419, filed Jul. 2, 2001, and Japanese Application 2002-057107, filed Mar. 4, 2002, the entireties of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stacked dielectric filter which constitutes a resonance circuit in a microwave band of several hundreds MHz to several GHz. In particular, the present invention relates to a stacked dielectric filter which makes it possible to effectively miniaturize communications equipment and electronics equipment.
2. Description of the Related Art
In recent years, there has been a strong demand to realize a small-sized and thin high frequency filter to be used for wireless communication equipment. Therefore, it is indispensable to use a stacked dielectric filter.
In general, as shown in
FIG. 30
, such a stacked dielectric filter, for example, a stacked dielectric filter
400
using a ¼ wavelength resonator has a plurality of resonant electrodes
402
,
404
, inner layer ground electrodes
406
,
408
,
410
,
412
, and a coupling-adjusting electrode
414
. Each of the plurality of resonant electrodes
402
,
404
has an end electrically connected to a ground electrode. Each of the inner layer ground electrodes
406
,
408
,
410
,
412
has an end electrically connected to the ground electrode. The inner layer ground electrodes
406
,
410
are stacked to sandwich a part of an open end of the resonant electrode
402
and a dielectric layer. The inner layer ground electrodes
408
,
412
are stacked to sandwich a part of an open end of the resonant electrode
404
and the dielectric layer. The coupling-adjusting electrode
414
electromagnetically couples the respective resonant electrodes
402
,
404
.
However, in the stacked dielectric filter
400
as shown in
FIG. 30
, the ground electric potential is used as the reference electric potential for inputting/outputting a signal of an unbalanced form. Therefore, for example, in order to connect the stacked dielectric filter
400
to a high frequency amplifying circuit of the balanced input type, it is necessary to use a balun (balanced-unbalanced converter) additionally between them. Consequently, a certain limit arises in the miniaturization.
In the above example, the stacked dielectric filter using the ¼ wavelength resonator is described. Additionally, stacked dielectric filters of the balanced type using ½ wavelength resonators have been also suggested (see, for example, Japanese Laid-Open Patent Publication 11-317603, 2000-353904, and 2000-22404).
In each of the stacked dielectric filters of the balanced type, the resonator length is inevitably increased, because the stacked dielectric filter is composed of the ½ wavelength resonator. Therefore, such a stacked dielectric filter is disadvantageous to realize a small sized filter.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a stacked dielectric filter of a small size which enables a balanced input/output for connection to a high frequency amplifying circuit or the like.
Another object of the present invention is to provide a stacked dielectric filter in which it is unnecessary to separately insert any circuit for connecting a DC power source to an IC when the IC is connected to an unbalanced-balanced converting section, while reducing the number of parts, suppressing the insertion loss, and miniaturizing the size of electronic devices including the IC.
Still another object of the present invention is to provide a stacked dielectric filter in which it is unnecessary to separately insert any circuit for matching the impedance between an unbalanced-balanced converting section and an IC when the IC is connected to the unbalanced-balanced converting section, and it is possible to reduce the number of parts, while suppressing the insertion loss, and miniaturizing the size of the electronic devices including the IC.
Still another object of the present invention is to provide a stacked dielectric filter which enables an increased degree of flexibility of design.
Still another object of the present invention is to provide a stacked dielectric filter in which it is possible to reduce the electrode area in a filter section, and it is possible to suppress the stray coupling in an unbalanced-balanced converting section.
The present invention provides a stacked dielectric filter comprising a filter section having a plurality of resonators for filtering an unbalanced signal, and at least one unbalanced-balanced converting section having strip lines. The filter section and the unbalanced-balanced converting sections are in a dielectric substrate including a plurality of stacked dielectric layers.
Accordingly, the filter section can be composed of the ¼ wavelength resonator by which it is advantageous to realize the miniaturization. It is possible to realize compact or small sized devices as compared with stacked dielectric filters of the balanced type composed of ½ wavelength resonators.
Further, it is unnecessary to set the characteristic impedance between the filter section and the unbalanced-balanced converting section to have a specified value (for example, 50&OHgr;). The characteristic impedance can be arbitrarily determined. Therefore, it is possible to enhance the degree of flexibility of design. Further, the filter section can be easily formed, and it is possible to widen the line width of the strip line of the balun section, because the characteristic impedance can be determined to be low. Therefore, it is possible to reduce the loss in the unbalanced-balanced converting section.
As described above, the present invention provides the stacked dielectric filter of the small size which enables the balanced input/output for connection to the high frequency amplifying circuit or the like.
In the stacked dielectric filter, the plurality of dielectric layers of different materials may be laminated or stacked to provide the dielectric substrate. Preferably, a dielectric constant of the dielectric layer corresponding to the filter section is higher than a dielectric constant of the dielectric layer corresponding tothe unbalanced-balanced converting section.
Accordingly, it is possible to reduce the electrode area in the filter section, and it is possible to suppress the stray coupling in the unbalanced-balanced converting section.
The stacked dielectric filter may be exemplarily constructed as follows. For example, the filter section is formed at an upper portion or a lower portion in a stacking direction of the plurality of dielectric layers of the dielectric substrate, and the unbalanced-balanced converting section is formed at a portion other than the upper portion and the lower portion. In this arrangement, an inner layer ground electrode for isolating the filter section from the unbalanced-balanced converting section can be easily formed between the filter section and the unbalanced-balanced converting section. Thus, it is possible to improve the characteristics.
Alternatively, the filter section may be formed at a left portion or a right portion in a stacking direction of the plurality of dielectric layers of the dielectric substrate, and the unbalanced-balanced converting section may be formed at a portion other than the left portion and the right portion.
Further, ground electrodes may be formed on both principal surfaces of the dielectric substrate, and planes on which resonant electrodes of the plurality of resonators are formed and planes on which the ground electrodes are formed may be parallel to one another. Planes on which input/output terminals of the filter section are formed and planes on which the strip lines of the unbalanced-balanced converting section are formed may be perpendicular to one another.
Alternatively, ground electrodes may be formed on both principal surfaces of the dielectric substrate, and planes on which resonant electrodes of the plurality of resonators are formed and planes on which t

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