Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1998-11-04
2002-04-23
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S230000, C333S202000, C333S219100
Reexamination Certificate
active
06377132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter having a coupling loop, to a duplexer, and to a communication device.
2. Description of the Related Art
As
FIG. 10
shows, a conventional filter
110
comprises a dielectric resonant device
120
, metal panels
111
having an external connector
113
that serves as an input-output connecting means and covers open portions of the dielectric resonant device
120
, and a coupling loop
112
.
The dielectric resonant device
120
includes a frame
121
and a dielectric resonator
122
that are made of ceramic. The frame
121
is shaped like a parallelepiped with two opposing surfaces being open, and is provided with conductors
123
thereon. The dielectric resonator
122
is shaped like a rectangular parallelepiped, and is disposed inside the frame
121
so that its two opposing surfaces are integrated with the frame
121
. The metal panels
111
are made of metal, such as iron or a nickel alloy, in order to achieve good electrical conductivity and to make the coefficient of linear expansion thereof the same as that of a dielectric. These metal panels
111
are connected to the conductors
123
of the dielectric resonant device
120
, whereby a cavity
130
is formed as a whole.
The coupling loop
112
is made of copper in view of electrical conductivity and rust prevention, and worked into the shape of an L. One end of the coupling loop
112
fits in a hole that is previously formed through the metal panel
111
, and is fixed by soldering or the like. The other end of the coupling loop
112
is connected to the external connector
113
. Since this other end of the coupling loop
112
is also worked into a corrugated shape, it can, for example, absorb impact that is applied from the side of the external connector
113
. This has solved problems, for example, deformation of the coupling loop
112
due to stress from the outside, and separation of the coupling loop
112
from the metal panel
111
.
In the filter
110
mentioned above, current applied from the outside flows in the coupling loop
112
via the external connector
113
. The current that flows through the coupling loop
112
generates a magnetic field, and this magnetic field couples with the dielectric resonator
122
. In this case, the degree of coupling between the coupling loop
112
and the dielectric resonator
122
is adjusted based on the length, thickness, and width of the coupling loop
112
or the distance between the coupling loop
112
and the dielectric resonator
122
. Such adjustment of the degree of coupling allows a filter having the required electrical characteristics.
A coupling loop has its own natural frequency, and the natural frequency of a coupling loop in a conventional filter is about 260 Hz. On the other hand, in normal use of the filter, a device itself, in which the filter is incorporated, vibrates with the vibrations applied from the outside. In this case, frequencies ranging from about 5 Hz to 200 Hz are a problem. There is a likelihood that a coupling loop will resonate with the vibrations from the outside. The coupling loop resonates because the frequency of the external vibrations is almost equivalent to the natural frequency of the coupling loop. Although the natural frequency of the conventional coupling loop does not coincide with the frequency of the external vibrations, if it remains about 260 Hz, the attenuation amount is not sufficient near about 200 Hz, which is an unnecessary signal, thereby affecting the filter characteristics to a degree that is not disregarded. As the coupling loop resonates with the external vibrations, the degree of coupling between the coupling loop and the dielectric resonator varies, and the electrical characteristics, such as return loss, are thereby disturbed. Moreover, reliability of the filter is deteriorated.
In order to solve the above problems, it may be possible to further increase the natural frequency of the coupling loop so that the resonance with the external vibrations can be disregarded. Incidentally, the coupling loop can be regarded as having a beam structure. In general, the natural frequency of a beam is expressed by the following formula:
Natural Frequency
f
=
C
l
2
EI
pA
where C is a constant, l is the length of the beam, E is the Young's modulus of the beam, I is the second moment of area of the beam, p is the density of the beam, and A is the sectional area of the beam.
Referring to the above formula, it may be possible to reduce the length of the beam in order to increase the natural frequency of the coupling loop. Since the length of the beam has an influence on the degree of coupling with the dielectric resonator, however, it cannot be easily changed. Accordingly, it is good, in practice, to change the bending rigidity of the beam. The bending rigidity of the beam is given by the product of the Young's modulus and the second moment of area of the material. Therefore, the bending rigidity of the beam can be improved by increasing the Young's modulus or the second moment of area of the material. Although iron is available as a material having a high Young's modulus, the use of iron for the coupling loop causes a new problem, that is, thorough rust prevention is required. When the coupling loop is made of iron, in general, intermodulation (IM) is apt to occur, and therefore, the coupling loop is plated with silver. If the silver plate rusts, however, iron appears on the surface thereof, and IM is likely to occur. Although it may also be possible to increase the thickness of the coupling loop in order to increase the second moment of area, this results in an increase in the material cost.
The coupling loop is formed by bending a metal plate into the shape of an L. Therefore, the strength of the bent portion is low, and this leads to a fear that the positional relationship between the coupling loop and the dielectric resonator may change.
Furthermore, one end of the coupling loop on the side of the external connector has been heretofore corrugated so as to absorb impact from the external connector. It is, however, not so easy to corrugate an end of the coupling loop, and costs become high.
SUMMARY OF THE INVENTION
The present invention has been made with a view toward solving the above problems. It is accordingly an object of the present invention to provide a filter, a duplexer, and a communication device that are hardly affected by vibrations applied from the outside and that have high reliability.
According to an aspect of the present invention, there is provided a filter having a cavity, an input-output connecting means mounted in the cavity, and a coupling loop connected to the input-output connecting means so as to couple with a magnetic field inside the cavity, wherein the coupling loop has a natural-frequency increasing means for increasing the natural frequency thereof.
According to another aspect of the present invention, there is provided a filter having a cavity, an input-output connecting means mounted in the cavity, and a coupling loop connected to the input-output connecting means so as to couple with a magnetic field inside the cavity, wherein the coupling loop is formed by bending a metal plate, and is provided with a rib extending in a direction that is not in parallel with a bending line.
According to a further aspect of the present invention, there is provided a filter having a cavity, an input-output connecting means mounted in the cavity, and a coupling loop connected to the input-output connecting means so as to couple with a magnetic field inside the cavity, wherein the coupling loop including a section having high rigidity and a curved section having low rigidity, one end of the high-rigidity section is connected to the cavity, the other end thereof is connected to one end of the low-rigidity curved section, and the other end of the low-rigidity curved section is connected to the input-output connecting means.
Preferably, a dielectric resonator is disposed inside the cavity.
Preferably, a
Himi Yoshihiro
Nakatani Yukihiro
Nishiyama Taiyo
Wakamatsu Hiroki
Jones Stephen E.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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