Nonreciprocal circuit device and communication apparatus...

Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type

Reexamination Certificate

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Details

C333S024200

Reexamination Certificate

active

06768392

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nonreciprocal circuit devices, and more particularly, it relates to nonreciprocal circuit devices such as isolators and circulators used in microwave bands, and communication apparatuses incorporating the nonreciprocal circuit devices.
2. Description of the Related Art
In general, a lumped-constant isolator adopted in a mobile communication apparatus such as a mobile phone passes a signal only in a direction in which the signal is transmitted, while blocking the signal transmission in the opposing direction. In addition, in the recent mobile communication apparatus, compact, lightweight, and low-priced products have been strongly demanded. With this tendency, a compact, lightweight, and low-priced isolator has been demanded.
As the lumped-constant isolator, there is known a device such as a lump-constant isolator
11
shown in FIG.
13
. In the lump-constant isolator
11
, a resin terminal case
13
is disposed on a metal lower case unit
12
having left and right walls
12
a
and a bottom wall
12
b
. A central electrode assembly
14
is contained in the terminal case
13
, and a metal upper case unit
15
is disposed on the structure. A permanent magnet
16
is attached to the inner surface of the metal upper case unit
15
. With the permanent magnet
16
, a direct current magnetic field is applied to the central electrode assembly
14
.
The central electrode assembly
14
is arranged by crossing three central electrodes
21
to
23
electrically insulated from each other at angles of 120 degrees on the upper surface of a microwave ferrite member
20
. Ports P
1
to P
3
of ends of the three central electrodes
21
to
23
are horizontally extracted, and a common shield part of the other ends thereof is in contact with the lower surface of the ferrite member
20
. The common shield part, which substantially covers the lower surface thereof, is connected to the bottom wall
12
b
of the lower case unit
12
via a window
13
a
of the terminal case
13
.
The ports P
1
to P
3
of the central electrodes
21
to
23
are connected to the hot-side capacitor electrodes of matching capacitors C
1
to C
3
. An end of a terminating resistor R is connected to the hot-side capacitor electrode of the matching capacitors C
3
. The central electrode assembly
14
and the capacitors C
1
to C
3
are contained in the terminal case
13
. Then, as shown in
FIG. 14
, the edges of two parts where the upper case unit
15
and the lower case unit
12
are close to each other (areas shown by vertical lines in
FIG. 14
) are connected by solder
18
(see FIG.
15
).
Meanwhile, the conventional isolator
11
forms a frame-like loop structure around the permanent magnet
16
and the central electrode assembly
14
in the upper case unit
15
and the lower case unit
12
. Thus, as shown in
FIG. 15
, a high frequency current i is likely to go around the upper and lower case units
15
and
12
. As a result, there is a problem of power consumption due to Joule loss. Moreover, the high frequency current i flowing through the case units
15
and
12
serves to cancel a regular signal current I flowing through the central electrodes
21
to
23
. In other words, the high frequency current i serves to reduce a high frequency magnetic field generated by the ferrite member
20
. As a result, the effective inductances of the central electrodes
21
to
23
and the effective magnetic permeability of the ferrite member
20
are reduced, thereby narrowing the operational frequency bandwidth of the isolator
11
.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device including a metal case through which a high frequency current is difficult to flow. In addition, it is another object of the present invention to provide a communication apparatus incorporating the nonreciprocal circuit device.
In order to accomplish the above objects, the present invention provides a nonreciprocal circuit device including a permanent magnet, a ferrite member which is adapted to receive a direct current magnetic field applied by the permanent magnet, the ferrite member including a plurality of central electrodes, and a metal case containing the permanent magnet, the ferrite member, and the plurality of central electrodes. In this nonreciprocal circuit device, the metal case has a gap for cutting off a loop current flowing around the ferrite member and the plurality of central electrodes.
In this case, a “gap” means an electrical gap. The gap of the present invention also includes a gap in which an insulating material is filled. In such a situation, although there is physically no gap, there is no electrical connection.
For example, the cross section of the metal case may have a substantially rectangular frame or cylindrical shape by bending a substantially rectangular metal plate at four positions in parallel to an edge of the metal plate. In addition, the metal case may be constituted of an upper case unit and a lower case unit. There may be disposed a gap at least between one edge of the upper case unit and an edge of the lower case unit opposite to the edge of the upper case unit. Furthermore, preferably, the metal case is set to be rotation-symmetrical with respect to the axis of the permanent magnet.
With the above arrangement, since a high frequency current flowing through the metal case is cut off by the gap disposed in the metal case, the high frequency current is difficult to flow through the metal case.
In addition, since the communication apparatus incorporating the above nonreciprocal circuit device in accordance with the present invention can have good frequency characteristics.


REFERENCES:
patent: 3324418 (1967-06-01), Caswell
patent: 3466571 (1969-09-01), Jansen et al.
patent: 3621476 (1971-11-01), Kanbayashi
patent: 4812787 (1989-03-01), Kuramoto et al.
patent: 6-140813 (1994-05-01), None
patent: 6-252611 (1994-09-01), None
patent: 6-260812 (1994-09-01), None
patent: 8-078911 (1996-03-01), None
patent: 11-168305 (1999-06-01), None

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