Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-03-15
2001-04-24
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219100, C333S227000, C333S212000, C331S096000
Reexamination Certificate
active
06222429
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter for selectively filtering a high-frequency signal having a desired frequency mainly used in a base station for a mobile communication system such as car telephones and portable telephones. More particularly, the present invention relates to a dielectric notch filter. The present invention also relates to a dielectric resonator constituting the dielectric filter.
2. Description of the Related Art
In recent years, as the development of the mobile communication system such as car telephones, a notch filter using a dielectric resonator is increasingly demanded.
Hereinafter, an exemplary conventional dielectric notch filter will be described with reference to figures.
FIGS. 24A and 24B
are external views of a conventional dielectric notch filter.
FIG. 24A
is a top view and
FIG. 24B
is a side view. In these figures, the dielectric notch filter includes cylindrical metal cavities
2401
, a base member
2402
, tuning members
2403
, and input/output terminals
2404
. The notch filter shown in
FIG. 24
has five resonators. A transmission line is formed in the base member
2402
and electromagnetically coupled with the respective dielectric resonators, so as to constitute the notch filter.
FIG. 25
shows the inside of a dielectric resonator used in the conventional dielectric notch filter shown in
FIG. 24
in a simplified manner. In the metal cavity
2401
, a dielectric block
2501
and a coupling loop
2502
for electromagnetic coupling are provided.
FIG. 26
is a cross-sectional view showing an adjusting mechanism for adjusting the degree of electromagnetic coupling in the conventional dielectric resonator. As shown in
FIG. 26
, the adjusting mechanism includes a supporting member
2
for supporting the dielectric block
2501
, a loop
4
a
of the coupling loop
2502
, a ground part
4
b
of the coupling loop
2502
, a handle
4
c
for rotating the whole coupling loop
2502
, and a pole
5
of the coupling loop
2502
. The pole
5
is composed of a center conductor
5
a
and an insulator
5
b
. The base member
2402
includes a transmission line
7
serving as an inner conductor and outer conductors
8
. The transmission line
7
is supported by a supporting member
9
which is an insulator. In general, the dielectric block
2501
is formed integrally with and supported by the supporting member
2
using glass with a low melting point. The operation principle of the conventional dielectric resonator having the above-described construction will be described below. When the dielectric block
2501
and the coupling loop
2502
are held in the metal cavity
2401
and the transmission line
7
is connected thereto, an electromagnetic field is produced in the cavity
2401
. Thus, the conventional dielectric resonator has a resonance frequency corresponding to a resonant mode. The degree of electromagnetic coupling of the dielectric resonator is a critical parameter for determining the electric characteristic of the dielectric resonator. The degree of electromagnetic coupling is determined depending on the number of lines of magnetic force across the cross section of the coupling loop
2502
. That is, according to the conventional technique, the coupling loop
2502
is mechanically rotated by the handle
4
c
and hence the effective cross-sectional area is varied, so that the number of lines of magnetic force across the coupling loop
2502
is adjusted.
In order to match the impedance of the dielectric resonator, the electric length of the coupling loop is precisely adjusted to be an odd-integer multiple of a quarter wavelength.
However, the above-described prior art has the following drawbacks.
(1) A complicated mechanism for mechanically rotating the coupling loop is required, and hence the number of components required is increased.
(2) The means for impedance matching is limited, and the size of the coupling loop is greatly increased for lower frequencies. Also, since the coupling loop is small for higher frequencies, it is impossible to attain a higher degree of coupling.
(3) In principle, the range of frequencies in which the impedance matching can be achieved is narrow.
(4) In order to melt the glass for adhesion, a heating treatment to the dielectric member is required. The adhesive strength of glass is low, and the mechanical reliability is poor.
As a result, the following problems arise.
(1) The coupling loop is easily rotated due to vibration and impact, so that the degree of electromagnetic coupling is varied.
(2) The production process is complicated.
(3) The production cost is increased.
SUMMARY OF THE INVENTION
The dielectric notch filter of this invention includes: a transmission line for transmitting a high-frequency signal; an input terminal and an output terminal provided at both ends of the transmission line; a ground conductor for supplying a ground potential; and a dielectric resonator connected to the ground conductor and the transmission line, wherein the dielectric notch filter further comprises impedance matching means connected to the ground conductor and the transmission line in parallel with the dielectric resonator, and the dielectric resonator includes: a cavity connected to the ground conductor; a dielectric block provided in the cavity; a coupling device coupled with an electromagnetic field produced in the cavity; and a coupling adjusting line for connecting the coupling device to the transmission line and for adjusting the degree of electromagnetic coupling.
In one embodiment of the invention, the degree of electromagnetic coupling is adjusted by an electrical length of the coupling adjusting line.
In an other embodiment of the invention, an impedance value of the impedance matching means in adjusted in accordance with an electrical length of the coupling adjusting line.
In another embodiment of the invention, the coupling adjusting line is formed of a TEM mode transmission line, and the degree of electromagnetic coupling is adjusted by a dielectric material inserted between the TEM mode transmission line and the ground conductor.
In another embodiment of the invention, the impedance matching means is an inductor. The inductor may be an air-core coil.
In another embodiment of the invention, the impedance matching means is a capacitor.
In another embodiment of the invention, the impedance matching means is a stub.
In another embodiment of the invention, the coupling adjusting line or the impedance matching means is formed by a conductor pattern provided in a dielectric substrate.
According to another aspect of the invention, the dielectric notch filter includes: a transmission line for transmitting a high-frequency signal; an input terminal and an output terminal provided at both ends of the transmission line; a ground conductor for supplying a ground potential; and a plurality of dielectric resonators connected to the ground conductor and the transmission line, wherein the dielectric notch filter further comprises a plurality of impedance matching means connected to the ground conductor and the transmission line in parallel with the plurality of dielectric resonators, and each of the dielectric resonators includes: a cavity connected to the ground conductor; a dielectric block provided in the cavity; a coupling device coupled with an electromagnetic field produced in the cavity; and a coupling adjusting line for connecting the coupling device to the transmission line and for adjusting the degree of electromagnetic coupling, resonance frequencies of the respective plurality of dielectric resonators being distributed symmetrically with respect to a filter center frequency.
In one embodiment of the invention, the. plurality of dielectric resonators are first to fifth. dielectric resonators, the first to fifth dielectrics resonators being arranged in a direction from the input terminal to the output terminal, and the first to fifth. dielectric resonators have resonance frequencies F1 to F5, respectively, the resonance frequencies F1 to F5 satis
Hatanaka Masami
Ishizaki Toshio
Nakamura Toshiaki
Saka Yuji
Satoh Yuki
Bettendorf Justin P.
Matsushita Electric - Industrial Co., Ltd.
Renner Otto Boisselle & Sklar
Summons Barbara
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