1. A tunable band-pass filter, comprising: a conductive chassis having a cavity resonator; a conductive cover to cover said cavity resonator; a resonant element arranged in said cavity resonator, one end of said resonant element being connected with said chassis and an other end being open end; and a movable conductor arranged in a space between said open end of said resonant element and said conductive cover.

2. The tunable band-pass filter according to claim 1, wherein there are a plurality of pieces of said cavity resonator, and said movable conductor is also deployed in a space between said cavity resonator and said cavity resonator.

3. The tunable band-pass filter according to any one of claims 1 to 2, wherein said movable conductor is connected by a non-conductivity material.

4. The tunable band-pass filter according to any one of claims 1 to 3, wherein movement of said movable conductor is a rotating movement.

5. The tunable band-pass filter according to any one of claims 1 to 3, wherein movement of said movable conductor is a linear movement.

6. The tunable band-pass filter according to any one of claims 1 to 5, having a frequency adjustment screw screwed in from said conductive cover in a manner facing said resonant element.

7. The tunable band-pass filter according to claim 6, wherein said movable conductor has a hole corresponding to said frequency adjustment screw.

8. The tunable band-pass filter according to any one of claims 1 to 7, wherein said movable conductor is a non-conductivity material having a metallic film formed on said non-conductivity material. 16

9. The tunable band-pass filter according to any one of claims 1 to 8, wherein said resonant element is one of a conductor and a dielectric, having a shape selected from a tabular shape, a prismatic column and a circular cylinder. 5 10. The tunable band-pass filter according to any one of claims 1 to 9, wherein a source of power of said movable conductor is a motor.

[Technical Field]
[0001]
The present invention relates to a band-pass filter used in a
10 microwave and a millimeter wave, and, more particularly, to a tunable
band-pass filter which can vary a resonance frequency.
[Background Art]
[0002]
In a radio communication system that performs transmission and
reception using a microwave or a millimeter wave band, a band-pass filter
is used to make only a signal of a desired frequency band pass, and to
remove a signal of an unnecessary bandwidth. When a band-pass filter is
used at a plurality of center frequencies, there is a technological case
described in patent literature 1. In patent literature 1, there is disclosed a
technology in which, in the metal housing of a semi-coaxial band-pass
filter, a dielectric having a movable structure is provided and a resonance
frequency of a resonator is made to be changed by moving this.
25 [Citation List]
[Patent Literature]
[0003]
[PTL 1] International Publication No. WO 2006/075439
15
20
3
[Summary of Invention]
[Technical Problem]
[0004]
However, in the technology described in patent literature 1, in order
5 to change a resonance frequency within a suitable range, a special
dielectric material, a dielectric material having a high permittivity such as
a compound of a rare-earth barium titanate system, for example, is required,
and, as a result, increase of cost is caused.
[0005]
10 Further, when forming a band-pass filter, it needs to be of a system
in which a dielectric member is used in each stage of a cavity semi-coaxial
resonator of a plurality of stages and these plurality of dielectric members
are moved simultaneously. At that time, there is a problem that the
structure becomes complicated because a holding member which joins a
15 dielectric member and a movable member connected with the dielectric
member is needed due to a difference of material between them.
[0006]
The present invention has been made in view of the
above-mentioned subject, and its object is to provide a tunable band-pass
20 filter which is of low cost and of a simple structure, and which can change
a resonance frequency of a resonator and a coupling amount (or, a coupling
coefficient) between resonators easily.
[Solution to Problem]
25 [0007]
A tunable band-pass filter of the present invention comprises: a
conductive chassis having a cavity resonator; a conductive cover to cover
said cavity resonator; a resonant element arranged in said cavity resonator,
one end of said resonant element being connected with said chassis and an
4
other end being open end; and a movable conductor arranged in a space
between said open end of said resonant element and said conductive cover.
[Advantageous Effects of Invention]
5 [0008]
According to a tunable band-pass filter of the present invention, it
becomes possible to provide a tunable band-pass filter which is of low cost
and of a simple structure, and which can change a resonance frequency of a
resonator and a coupling amount between resonators easily.
10
[Brief Description of Drawings]
[0009]
[Fig. 1 A] Fig. 1A is a perspective view showing a structure of a
tunable band-pass filter of a first exemplary embodiment of the present
15 invention.
[Fig. IB] Fig. IB is a sectional view showing a structure of a
tunable band-pass filter of the first exemplary embodiment of the present
invention.
[Fig. 2] Fig. 2 is a perspective view showing a structure of a
20 tunable band-pass filter of the first exemplary embodiment of the present
invention.
[Fig. 3A] Fig. 3A is a perspective view showing a structure of a
tunable band-pass filter of a second exemplary embodiment of the present
invention.
25 [Fig- 3B] Fig. 3B is a perspective view showing a structure of a
movable conductor part of the second exemplary embodiment of the
present invention.
[Fig. 4] Fig. 4 is a perspective view showing a structure of a
tunable band-pass filter of a third exemplary embodiment of the present
5
invention.
[Fig. 5] Fig. 5 is a perspective view showing a structure of a
tunable band-pass filter of a fourth exemplary embodiment of the present
invention.
5 [Fig. 6] Fig. 6 is a diagram showing a change of a resonance
frequency of a tunable band-pass filter of the first exemplary embodiment
of the present invention.
[Description of Embodiments]
10 [0010]
Hereinafter, an exemplary embodiment of the present invention will
be described in detail with reference to a drawing. However, although
limitation that is technically preferred to carry out the present invention is
being imposed to exemplary embodiments described below, the scope of
15 the invention is not limited to the followings.
(First exemplary embodiment)
A tunable band-pass filter of the first exemplary embodiment of the
present invention will be described in detail using Fig. 1A and Fig. IB.
Fig. 1A is a perspective view showing a structure of the first exemplary
20 embodiment of the present invention. In Fig. 1A, there is indicated a
band-pass filter including pieces of cavity resonator 20 of three stages.
Fig. IB indicates a sectional view of one piece of cavity resonator 20
among the pieces of cavity resonator 20 of three stages shown in Fig. 1A.
[0011]
25 The cavity resonator 20 is formed by a combination of a conductive
chassis 1 and a conductive cover 2. Although the cavity resonator 20 is
of a cylindrical shape in Fig. 1A, it is not limited to a cylindrical shape,
and it may be of another shape such as a prismatic shape. A window 21
of a structure made by cutting out a part of said cylindrical shape connects
6
between each cavity resonator. The shape of the window 21 is not limited
to the shape shown in Fig. 1A, and it may be of a shape besides this shape
such as a cylinder, and the width of the cutout may be made to be about the
same as the diameter of the cylinder of the cavity resonator 20.
5 [0012]
A resonant element 3 is installed in the cavity resonator 20, and its
one end is connected to the conductive chassis 1 and the other end which is
in the side facing the conductive cover 2 is open. As a shape of the
resonant element 3, a tabular shape, a prism or a column is possible, but
10 not limited to these. For example, a shape having a bend of an L
letterform is also possible. As material of the resonant element 3, a
conductor or a dielectric is possible.
[0013]
There are provided, in the cavity resonators of the both ends among
15 the three pieces of cavity resonator 20 which form a band-pass filter, an
input terminal 7 for inputting a radio wave from outside and exciting said
resonant element 3 and an output terminal 8 for outputting a radio wave
which has passed said plurality of pieces of resonant element 3 outside the
chassis. In Fig. 1A, although a three-stage band-pass filter having three
20 pieces of cavity resonator 20 is being disclosed, the number of pieces of
cavity resonator 20 is not limited. Furthermore, the input terminal 7 and
the output terminal 8 are ones which have been defined for convenience of
description of operation, and thus it is possible to input a radio wave from
the output terminal 8, and take out a radio wave from the input terminal 7.
25 [0014]
There is arranged a conductor 5 made of a conductive member
between each piece of resonant element 3 and the conductive cover 2. An
inexpensive metal such as copper and aluminum is possible as the material
of the conductor 5. The conductor 5 is arranged for each piece of cavity
7
resonator 20, and neighboring pieces of conductor 5 are connected by a
non-conductive member 6. As the non-conductive member 6, an
inexpensive member such as ceramic and resin is possible. In order to
connect the non-conductive member 6 and the conductor 5, a connection
5 member (no code attached in Fig. 1A) may be provided between the
non-conductive member 6 and the conductor 5. Although the material of
this connection member is optional, it is possible to use an inexpensive
member of metal, ceramic or resin. The conductor 5 may be one having a
size and a shape different for each piece of cavity resonator 20.
10 [0015]
Among the both ends of the train of pieces of conductor 5 connected
by pieces of non-conductive member 6, one end penetrates through the
conductive chassis 1 by a support 9, and, in addition, is made to be able to
rotate about an axis to make the conductor 5 be movable from outside of
15 the conductive chassis 1 of the band-pass filter. Here, said one end does
not need to penetrate. The other end penetrates through the conductive
chassis 1, is taken out outside, and is also made to be able to be
axis-rotated. As motive power of this axial rotation, a stepping motor 10
or the like whose rotation is controlled by a computer can be used although
20 manual may be acceptable.
[0016]
Fig. IB is a diagram showing a sectional structure of one piece of
cavity resonator 20 constituting a band-pass filter shown in Fig. 1A. By
rotating in the directions indicated by the arrows in this figure about a
25 supporting point 12, the conductor 5 changes the capacity between the
resonant element 3 and itself, and changes a resonance frequency. That is,
by making the conductor 5 rotate, the capacity is changed by the interval
between the conductor 5 and the resonant element 3 changing. In the case
of Fig. IB, a resonance frequency can be lowered along with rotation
8
toward downward direction shown by the arrow in this figure. Here,
there is used a frequency adjustment screw 4 to determine a standard
resonance frequency of the cavity resonator 20. However, it is not
indispensable as a function of a tunable band-pass filter. In Fig. 1A,
5 there is indicated a case where the frequency adjustment screw 4 does not
exist.
[0017]
According to the exemplary embodiment disclosed above, a
band-pass filter is inexpensive because the conductor 5 made of metal such
10 as copper and aluminum that is of low cost is used between each resonant
element 3 and the conductive cover 2. Furthermore, its structure is
simple because the conductor 5 is not a dielectric member and thus is easy
to be connected with a moving member, resulting in a holding member that
would be necessary to join a dielectric member or the like being
15 unnecessary. That is, as an effect of this exemplary embodiment, it is
possible to provide a tunable band-pass filter which is of an inexpensive
and of an easy structure, and which can change a resonance frequency of
the cavity resonator 20 easily.
[0018]
20 Further, using Fig. 2, a tunable band-pass filter which can, in
addition to the above effect, change a coupling amount between pieces of
cavity resonator 20 is disclosed. A coupling amount or a coupling
coefficient is related to a band of a band-pass filter, and when it is large, a
band is wide, and, when it is small, a band is narrow. Fig. 2 indicates a
25 structure in which a conductor 5b that is similar to the conductor 5 is also
provided in a position corresponding to the window 21 between pieces of
cavity resonator 20. Each piece of conductor 5 and a piece of conductor
5b are connected via a non-conductive member 6b.
[0019]
9
The conductor 5b has a function to adjust a coupling amount
between pieces of cavity resonator 20. That is, a coupling amount
between pieces of cavity resonator 20 changes according to a resonance
frequency of the cavity resonator 20 being changed by the conductor 5
5 provided above the resonant element 3. These pieces of conductor 5b do
not need to be of an identical size and a shape among respective pieces of
cavity resonator 20, and a size and a shape that are suitable for each of
them can be selected.
[0020]
10 Next, an effect in this exemplary embodiment will be described
using Fig. 6. Fig. 6 indicates a state of a change in a resonance frequency
of a band-pass filter of 8000 MHz band when, in the structure of Fig. 1 A,
rotating the conductor 5 in the downward direction of the arrow in the
figure. At that time, the diameter of the cavity resonator 20 is 11 mm and
15 the length 1 1 mm, and the width of the conductor 5 is 6 mm, the length 8
mm and the thickness 0.5 mm. The conductor 5 is in a position that is 8
mm from the bottom base of the cavity resonator 20, and the supporting
point 12 of rotation is in a position that is offset from the center axis of the
cavity resonator 20 by 3 mm. An inclined angle of 0 degree indicates a
20 state that the conductor 5 is parallel to the conductive cover 2. By
changing the angle of rotation from 0 degree to 15 degrees, a resonance
frequency has declined by about 300 MHz. There are almost no
return-loss deteriorations during that span.
[0021]
25 As above, according to this exemplary embodiment, a tunable
band-pass filter which is inexpensive and of a simple structure and which
can change a resonance frequency of a cavity resonator and a coupling
amount between cavity resonators easily can be provided.
(Second exemplary embodiment)
10
The second exemplary embodiment of the present invention will be
described using Fig. 3A and Fig. 3B. Fig. 3A is a structure in which, in
place of the conductor 5 of the first exemplary embodiment, a conductor 5d
shown in Fig. 3B is formed on the face of a non-conductive member 5c in
5 the side of the resonant element 3. Fig. 3B shows a conductor structure
used in Fig. 3A. For example, a structure in which the conductor 5d made
of a metallic film such as copper is formed on the non-conductive member
5c such as a printed wiring board can be used as a conductor. The
conductor structure in which the conductor 5d is formed onto the
10 non-conductive member 5c is connected by a connection member (no code
attached in Fig. 3B) forming a rotating shaft.
[0022]
The other components in this exemplary embodiment are the same
as those of the first exemplary embodiment. That is, according to this
15 exemplary embodiment, a tunable band-pass filter which is inexpensive
and of a simple structure, and which can change a resonance frequency of a
cavity resonator and a coupling amount between cavity resonators easily
can be provided.
(Third exemplary embodiment)
20 The third exemplary embodiment of the present invention will be
described using Fig. 4. Fig. 4 is a structure in which, in place of the
conductor 5 of the first exemplary embodiment, a conductor 5e having a
hole 13 which can let the frequency adjustment screw 4 through is provided.
As a result, it also becomes possible to carry out frequency adjustment
25 using the frequency adjustment screw 4 without influence of rotation of the
conductor 5e, and thus a variable range of a resonance frequency as a
band-pass filter can be expanded.
[0023]
The other components of this exemplary embodiment are the same
11
as those of the first exemplary embodiment. That is, according to this
exemplary embodiment, a tunable band-pass filter which is inexpensive
and of a simple structure and which can change a resonance frequency of a
cavity resonator and a coupling amount between cavity resonators easily
5 can be provided.
(Fourth exemplary embodiment)
The fourth exemplary embodiment of the present invention will be
described using Fig. 5. Fig. 5 is a structure in which, in place of the
rotating mechanism of the conductor 5 of the first exemplary embodiment,
10 a rotational movement of a motor 10 is converted into an up and down
movement by a gear 1 1 to make the conductor 5 move up and down. By
moving it up and down, a resonance frequency can be changed by a
distance between the conductor 5 and the resonant element 3 changing.
[0024]
15 The other components of this exemplary embodiment are the same
as those of the first exemplary embodiment. That is, according to this
exemplary embodiment, a tunable band-pass filter which is inexpensive
and of a simple structure and which can change a resonance frequency of a
cavity resonator and a coupling amount between cavity resonators easily
20 can be provided.
[0025]
Various transformations are possible to the present invention within
the scope of the invention described in the claims without limited to the
above-mentioned exemplary embodiments, and it goes without saying that
25 those are also included within the scope of the present invention. Part or
all of the above-mentioned exemplary embodiments can also be described
like the following supplementary notes, but not limited to them.
[0026]
Supplementary note
12
(Supplementary note 1)
A tunable band-pass filter, comprising: a conductive chassis having
a cavity resonator; a conductive cover to cover said cavity resonator; a
resonant element arranged in said cavity resonator, one end of said
5 resonant element being connected with said chassis and an other end being
open end; and a movable conductor arranged in a space between said open
end of said resonant element and said conductive cover.
(Supplementary note 2)
The tunable band-pass filter according to supplementary note 1,
10 wherein there are a plurality of pieces of said cavity resonator, and said
movable conductor is also deployed in a space between said cavity
resonator and said cavity resonator.
(Supplementary note 3)
The tunable band-pass filter according to any one of supplementary
15 notes 1 to 2, wherein said movable conductor is connected by a
non-conductivity material.
(Supplementary note 4)
The tunable band-pass filter according to any one of supplementary
notes 1 to 3, wherein movement of said movable conductor is a rotating
20 movement.
(Supplementary note 5)
The tunable band-pass filter according to any one of supplementary
notes 1 to 3, wherein movement of said movable conductor is a linear
movement.
25 (Supplementary note 6)
The tunable band-pass filter according to any one of supplementary
notes 1 to 5, having a frequency adjustment screw screwed in from said
conductive cover in a manner facing said resonant element.
(Supplementary note 7)
13
The tunable band-pass filter according to supplementary note 6,
wherein said movable conductor has a hole corresponding to said
frequency adjustment screw.
(Supplementary note 8)
5 The tunable band-pass filter according to any one of supplementary
notes 1 to 7, wherein said movable conductor is a non-conductivity
material having a metallic film formed on said non-conductivity material.
(Supplementary note 9)
The tunable band-pass filter according to any one of supplementary
10 notes 1 to 8, wherein said resonant element is one of a conductor and a
dielectric, having a shape selected from a tabular shape, a prismatic
column and a circular cylinder.
(Supplementary note 10)
The tunable band-pass filter according to any one of supplementary
15 notes 1 to 9, wherein a source of power of said movable conductor is a
motor.
(Supplementary note 11)
The tunable band-pass filter according to supplementary note 10,
wherein said motor is controlled by a computer.
20 [0027]
This application claims priority based on Japanese application
Japanese Patent Application No. 2012-233659 filed on October 23, 2012,
the disclosure of which is incorporated herein in its entirety.
25 [Industrial Applicability]
[0028]
The present invention relates to a band-pass filter used in a
microwave and a millimeter wave, and, more particularly, to a tunable
band-pass filter which can vary a resonance frequency.
14
[Reference signs List]
[0029]
1 Conductive chassis
2 Conductive cover
3 Resonant element
4 Frequency adjustment screw
5, 5b, 5d and 5e Conductor
5c Non-conductive member
6 and 6b Non-conductive member
7 Input terminal
8 Output terminal
9 Support
10 Motor
11 Gear
12 Supporting point
13 Hole
20 Cavity resonator
21 Window

WE CLAIM:
1. A tunable band-pass filter, comprising: a conductive chassis
having a cavity resonator; a conductive cover to cover said cavity
resonator; a resonant element arranged in said cavity resonator, one end of
said resonant element being connected with said chassis and an other end
being open end; and a movable conductor arranged in a space between said
open end of said resonant element and said conductive cover.
2. The tunable band-pass filter according to claim 1, wherein
there are a plurality of pieces of said cavity resonator, and said movable
conductor is also deployed in a space between said cavity resonator and
said cavity resonator.
3. The tunable band-pass filter according to any one of claims
1 to 2, wherein said movable conductor is connected by a non-conductivity
material.
4. The tunable band-pass filter according to any one of claims
1 to 3, wherein movement of said movable conductor is a rotating
movement.
5. The tunable band-pass filter according to any one of claims
1 to 3, wherein movement of said movable conductor is a linear movement.
6. The tunable band-pass filter according to any one of claims
1 to 5, having a frequency adjustment screw screwed in from said
conductive cover in a manner facing said resonant element.
7. The tunable band-pass filter according to claim 6, wherein
said movable conductor has a hole corresponding to said frequency
adjustment screw.
8. The tunable band-pass filter according to any one of claims
1 to 7, wherein said movable conductor is a non-conductivity material
having a metallic film formed on said non-conductivity material.
16
9. The tunable band-pass filter according to any one of claims
1 to 8, wherein said resonant element is one of a conductor and a dielectric,
having a shape selected from a tabular shape, a prismatic column and a
circular cylinder.
5 10. The tunable band-pass filter according to any one of claims
1 to 9, wherein a source of power of said movable conductor is a motor.