Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1998-03-05
2001-02-06
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S202000, C333S219100
Reexamination Certificate
active
06184758
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric resonator, a filter, a duplexer and a communication apparatus for use in the bands of microwaves, millimeter waves and so on.
2. Description of the Related Art
Recently, high-capacity and high-speed communication systems have been required to cope with a rapid increase in needs of mobile communication systems and a quick shift to the multimedia society. In response to an increased amount of information to be communicated, the frequency band for use in communications is going to be enlarged from the microwave band to the millimeter-wave band. In the millimeter-wave band, a conventional TE01&dgr;-mode dielectric resonator formed of a columnar dielectric can also be used as in the microwave band. The resonance frequency of the TE01&dgr;-mode dielectric resonator is determined depending on the externals dimensions of the columnar dielectric, and strict machining accuracy has been required to achieve the desired resonance frequency. Because the outer circumference and height of the columnar dielectric are set by grinding, it has been difficult to precisely set strict dimensions with respect to the resonance frequency in the millimeter-wave band where stricter machining accuracy is required.
Also, when a dielectric filter is constructed by arranging a plurality of TE01&dgr;-mode dielectric resonators in a metallic case with predetermined intervals between, the resonators have been required to be arranged with high position accuracy because the coupling between input/-output means such as a metallic loop and the dielectric resonator or the coupling between the dielectric filter and the dielectric resonator is determined depending on the distance between those components.
With a view of solving the above problems, the inventors have proposed in Japanese Patent Application No. 7-62625 a dielectric resonator superior in machining accuracy and a dielectric filter superior in position accuracy.
A basic construction of the dielectric filter according to the above Japanese Patent Application is shown in FIG.
6
.
FIG. 6
is an exploded perspective view of the dielectric filter according to the above Japanese Patent Application.
As shown in
FIG. 6
, a dielectric filter
101
is made up of a dielectric substrate
102
and a pair of upper and lower conductor cases
103
,
104
.
The dielectric substrate
102
is a substrate having a predetermined relative dielectric constant, and has an electrode
102
a
formed all over one principal plane thereof except two circular openings
102
c
each having a predetermined diameter and an electrode
102
b
formed all over the other principal plane thereof except two circular openings
102
d
each having a predetermined diameter. The openings
102
c
,
102
d
each formed two in the respective principal planes are positioned to face each other.
The upper conductor case
103
is made of a metal and has a box-like shape with a lower surface being open. Also, the upper conductor case
103
is arranged while leaving a spacing from the dielectric substrate
102
near the openings
102
c
in the electrode
102
a.
The lower conductor case
104
is made of a dielectric and has a box-like shape with an upper surface being open and flanges laterally projecting at the bottom. Also, a shield conductor
106
is formed on an inner peripheral surface of the lower conductor case
104
, and input/output electrodes
105
a
,
105
b
are formed in positions facing the two openings
102
d
in the electrode
102
b
, respectively, in such a manner as isolated from the shield conductor
106
. The input/output electrodes
105
a
,
105
b
are led out respectively through holes
104
a
,
104
b
formed in a side surface of the lower conductor case
104
.
Further, a pair of spacers
107
are disposed in the lower conductor case
104
to keep a predetermined spacing between an inner bottom surface of the lower conductor case
104
, on which the shield conductor
106
is formed, and the dielectric substrate
102
. The spacers
107
are made of a dielectric material having a so low dielectric constant as not to disturb the electromagnetic field in the upper and lower conductor cases
103
,
104
.
In the dielectric filter having such a structure, electromagnetic energy is confined in the dielectric substrate
102
near its portions each sandwiched between the two opposing openings
102
c
,
102
d
in the electrodes
102
a
,
102
b
, causing those portions to serve as two TE010 mode resonators. As a result, a dielectric filter having resonators in two stages is obtained.
With the above-stated construction, the resonance areas are defined by the size of the openings in the electrodes and the openings can be formed by etching or ether like technique in the manufacture process. Hence a dielectric filter can be manufactured in which dimensional accuracy of resonators and position accuracy between the resonators with respect to the resonance frequency are very precisely reproduced.
In the above dielectric filter
101
, however, since electromagnetic energy is confined at a high degree, the coupling between the resonators adjacent to each other has been inevitably weak. Accordingly, when the dielectric filter
101
is manufactured in practice, a narrow-band filtering characteristic has been necessarily resulted due to the weak coupling between the resonators adjacent to each other.
More specifically, when the dielectric filter
101
having a central frequency of 25 GHz was manufactured on condition that a dielectric ceramic substrate being 10 mm×6 mm square and 1 mm thick and having a relative dielectric constant of
24
was used as the dielectric substrate
102
, the electrodes
102
a
,
102
b
were made of gold, the diameter of the openings
102
c
,
102
d
was 3.5 mm, the distance (gap) between the two openings
102
c
adjacent to each other or the distance (gap) between the two openings
102
d
adjacent to each other was 0.1 mm, the distance from the inner ceiling surface of the upper conductor case
103
to the upper surface of the dielectric substrate
102
was 1 mm, and the distance from the lower surface of the dielectric substrate
102
to the inner bottom surface of the lower conductor case
104
was 1 mm, the coupling coefficient was less than 1.5% and a resulting band-pass filter had a narrow band with a relative pass band width of approximately 300 MHz.
To make wider the band width of such a band-pass filter, it is conceivable to increase the coupling coefficient by reducing the distance between the resonators (the distance, i.e., gap, between the two openings
102
c
adjacent to each other or the distance between the two openings
102
d
adjacent to each other). There is however a limit in reducing the distance (gap) between the resonators. In practice, a limit of the distance (gap) between the resonators is 0.01 mm. It has been proved that, even in reducing the gap to such a limit value, the coupling coefficient is approximately 2% and the relative pass band width is approximately 400 MHz at maximum.
Furthermore, reducing the distance between the resonators means is equivalent to making smaller the distance between the two openings
102
c
adjacent to each other or the distance between the two openings
102
d
adjacent to each other, and hence has accompanied another problem of making it more difficult to effect patterning of the electrode
102
a
or
102
d.
In addition, because of weak external coupling between the input/output electrodes
105
a
,
105
b
and the resonators, it has been necessary to optimally arrange the position relationship between the two openings
102
d
, which are formed in the electrode
102
b
on the other principal plane of the dielectric substrate
102
, and the dielectric strips
105
a
,
105
b
for the sake of providing the required external coupling. There has been a difficulty in design of the above optimum arrangement.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problems as set forth above, and its object is to
Hiratsuka Toshiro
Ida Yutaka
Ishikawa Yohei
Kanagawa Kiyoshi
Mikami Shigeyuki
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
Summons Barbara
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