Dielectric resonator devices, dielectric filters and...

Details Dielectric resonator devices, dielectric filters and... Dielectric resonator devices, dielectric filters and...

2002-07-18

2004-03-09

Young, Brian (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S202000, C333S222000, C333S101000

Reexamination Certificate

active

06703912

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to dielectric resonator devices, dielectric filters and dielectric duplexers for use in communications devices, image devices, etc.
BACKGROUND OF THE INVENTION
Mobile communications systems using a frequency band of hundreds of megahertz to several gigahertz have terminal devices comprising a receiving circuit
52
and a transmitting circuit
62
which are connected in parallel with an antenna
7
via a duplexer
72
to use the single antenna
7
for both the receiving circuit
52
and the transmitting circuit
62
as shown in FIG.
35
. The duplexer
72
comprises a receiving filter
50
and a transmitting filter
60
, each of which is provided, for example, by a coaxial dielectric resonator
20
shown in FIG.
38
.
With reference to
FIG. 38
, the coaxial dielectric resonator
20
comprises a rectangular parallelepipedal dielectric block
21
having a bore
22
extending therethrough, an outer conductor layer
24
and an inner conductor layer
23
which are formed on the dielectric block
21
respectively over the outer peripheral surface thereof and the inner peripheral surface thereof defining the bore
22
, and a short-circuiting conductor layer
25
formed on the dielectric block
21
over an end face thereof where the bore
22
has an opening and providing a short circuit between the outer conductor layer
24
and the inner conductor layer
23
.
With reference to FIG.
39
(
a
) showing the coaxial dielectric resonator
20
, the outer conductor layer
24
is connected to the ground, and the inner conductor layer
23
to a signal input terminal S, whereby the coaxial dielectric resonator
20
is made equivalent to a circuit comprising an inductance element and a capacitance element which are connected in parallel with each other as shown in FIG.
39
(
b
), thus providing a trap filter having a resonance frequency which is determined by the inductance of the inductance element L and the capacitance of the capacitance element C.
Terminal devices which are usable for a plurality of communications systems of different frequency bands are required of mobile communications systems. Accordingly, it has been proposed to use a dielectric resonator device shown in
FIG. 37
(see, for example, JP-A No. 7-147503/1995) for the receiving filter
50
and transmitting filter
60
.
The dielectric resonator device is provided by connecting a switch SW to the point of connection between the inner conductor layer
23
of the coaxial dielectric resonator
20
and the signal input terminal S, via an external capacitor element C
0
, such that the capacitance C
0
of the external capacitor element can be connected to or disconnected from a capacitance C provided between the outer conductor layer
24
of the resonator
20
and the inner conductor layer
23
thereof by operating the switch SW. The resonance frequency of the resonator
20
alters with the variation of capacity effected by switching.
FIG. 36
shows an arrangement of a receiving filter
50
and a transmitting filter
60
each comprising such a dielectric resonator device. As illustrated, the receiving filter
50
has a signal line extending from a receiving connection terminal
51
to an antenna terminal
71
, and a plurality of capacitance elements C
4
, C
5
and C
6
provided on the signal line. The transmitting filter
60
has a signal line extending from a transmitting connection terminal
61
to the antenna terminal
71
, and a plurality of capacitance elements C
4
′, C
5
′ and C
6
′ provided on the signal line. Two coaxial dielectric resonators
20
,
20
are connected to each of the signal lines. A switch SW is connected via a capacitance element C
0
to the point of connection between each resonator
20
and the signal line. Accordingly, the pass bands of the receiving filter
50
and the transmitting filter
60
can be altered for a changeover between two kinds of receiving/transmitting frequencies by operating these switches SW.
It has been demanded in recent years that mobile communications terminal devices, such as portable telephones, be made ever smaller in size, giving rise to the great problem of how to reduce the number of electric or electronic components and how to diminish the sizes of such components. However, the dielectric resonator device shown in
FIG. 37
has the problem that the need to connect the external capacitor C
0
in the form of a chip to the coaxial dielectric resonator
20
increases the number of components of the device and makes the device large-sized. Further since chip capacitors are great in capacity tolerance, the capacitor requires an additional circuit (not shown) for finely adjusting the capacity, hence a further increase in the number of components.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dielectric resonator device having a resonance frequency which is accurately variable without necessitating an external capacitor, and a dielectric filter and a dielectric duplexer which comprise the resonator device.
The present invention provides a dielectric resonator device comprising a coaxial dielectric resonator
2
which comprises a dielectric block
21
having a bore
22
extending therethrough, an outer conductor layer
24
formed on an outer peripheral surface of the dielectric block
21
, an inner conductor layer
23
formed on the dielectric block
21
over an inner peripheral surface thereof defining the bore
22
, a short-circuiting conductor layer
25
formed on the dielectric block
21
over an end face thereof where the bore
22
has an opening and providing a short circuit between the outer conductor layer
24
and the inner conductor layer
23
, and a separated conductor layer
3
formed on the outer peripheral surface of the dielectric block
21
and electrically separated from the outer conductor layer
24
.
The separated conductor layer
3
of the resonator
2
has connected thereto a switch SW by which the capacitance C′ provided between the separated conductor layer
3
and the inner conductor layer
23
is connected to or disconnected from the capacitance C provided between the outer conductor layer
24
and the inner conductor layer
23
upon switching to thereby vary the resonance frequency of the resonator
2
.
With the dielectric resonator device of the invention, the inner conductor layer
3
of the resonator
2
is connected, for example, to a signal input terminal S, and the outer conductor layer
24
is connected to the ground.
With the device described above, the separated conductor layer
3
on the outer peripheral surface of the dielectric block
21
of the resonator
2
is opposed to the inner conductor layer
23
, providing a capacitance C′ between the two layers. The capacitance C′ is connected to or disconnected from the capacitance C between the outer conductor layer
24
and the inner conductor layer
23
by operating the switch SW, thus performing the same function as a conventional external capacitor.
Stated more specifically, the separated conductor layer
3
of the resonator
2
is connected to the ground via the switch SW. Accordingly, when closed, the switch SW connects the separated conductor layer
3
to the ground, whereby the capacitance C′ between the separated conductor layer
3
and the inner conductor layer
23
is connected to the capacitance C between the outer conductor layer
24
and the inner conductor layer
23
to shift the resonance frequency of the resonator
2
toward the lower frequency side. Alternatively when opened, the switch SW cuts off the separated conductor layer
3
from the ground, with the result that the capacitance C′ between the separated conductor layer
3
and the inner conductor layer
23
becomes no longer involved in the resonance frequency of the resonator
2
to shift the resonance frequency toward the higher frequency side.
Further stated more specifically, the separated conductor layer
3
of the resonator
2
is provided by forming a groove
26
in the outer conductor layer
2

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