Wave transmission lines and networks – Coupling networks – Nonreciprocal gyromagnetic type
Reexamination Certificate
2003-09-04
2004-11-23
Jones, Stephen E. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Nonreciprocal gyromagnetic type
C333S001100
Reexamination Certificate
active
06822527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an isolator utilizing the Faraday effect.
2. Description of the Related Art
FIG. 4
shows a main portion of a conventional isolator. A magnetic core
21
constructed by ferrite of a disc shape such as YIG, etc. is placed within a direct current magnetic field generated from an unillustrated permanent magnet, and its upper face is perpendicular to the direction of the direct current magnetic field. Three central conductors (first central conductor
22
, second central conductor
23
and third central conductor
24
) are placed on the upper face of the magnetic core
21
, and are held so as to be overlapped with each other at an equal angle interval (120°) by mutually holding their insulations approximately in the central portion of the upper face of the magnetic core
21
. Their lengths are approximately equal to each other so that their inductance values are also approximately equal to each other.
Each of the central conductors
22
to
24
is constructed by two parallel band-shaped conductors, and one end of each central conductor is connected to the ground. The other end
22
a
of the first central conductor
22
is set to an input terminal, and the other end
23
a
of the second central conductor
23
is set to an output terminal. The other ends
22
a
,
23
a
are respectively connected to the ground by capacitors
25
,
26
for matching.
On the other hand, the other end
24
a
of the third central conductor is connected to the ground by a terminal end resistor
27
and a terminal end capacitor
28
.
In the above construction, a signal inputted to the other end
22
a
of the first central conductor
22
is outputted to the other end
23
a
of the second central conductor
23
by the Faraday effect.
However, a signal of the reverse direction inputted to the other end
23
a
of the second central conductor
23
is oppositely absorbed by the third central conductor
24
and the terminal end resistor
27
and the terminal end capacitor
28
connected to this third central conductor
24
, and is not outputted to the other end of the first central conductor
22
. A transmitting state of this signal of the reverse direction will be explained by
FIG. 5
constructed by replacing this transmitting state with an equivalent electric circuit.
In
FIG. 5
, an inductance element
31
connected to the other end
23
a
of the second central conductor
23
is represented by the third central conductor
23
, and an inductance element
32
connected to the other end
22
a
of the first central conductor
22
is represented by the first central conductor
22
. A capacity element
33
between the two inductance elements
31
and
32
is represented by a coupling capacitor between the two central capacitors
22
and
23
.
One end of an inductance element
34
represented by the third central conductor
24
is connected to both ends of the capacitor element, and the other end is connected to the ground by the terminal end resistor
27
and the terminal end capacitor
28
. Accordingly, a series resonance circuit is constructed by the inductance element
34
and the terminal end capacitor
28
, and a signal is greatly attenuated at a resonance frequency F
0
as shown in FIG.
3
.
However, since a frequency band for attenuating the signal transmitted in the reverse direction is narrow in the above construction, a problem exists in that the attenuating amount R is reduced with respect to the signal transmission of a wide frequency band (from F
1
to F
2
) and the signal level reflected to the input terminal is increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an isolator for greatly attenuating the signal transmitted in the reverse direction over the wide frequency band.
To solve the above problem, the present invention resides in an isolator comprising a magnetic core of a plate shape placed within a direct current magnetic field and having an upper face perpendicular to the direction of the direct current magnetic field, and first to third central conductors placed so as to be overlapped with each other at an equal angle interval approximately in the central portion of the upper face of the magnetic core, and respectively having one end connected to the ground, wherein the other end of the first central conductor is set to an input terminal, and the other end of the second central conductor is set to an output terminal, and at least the third central conductor is constructed by two parallel band-shaped conductors, and the other end of one band-shaped conductor is connected to the ground by a first resistor and a first capacitor, and the other end of the other band-shaped conductor is connected to the ground by a second resistor and a second capacitor, and the capacity value of the first capacitor and the capacity value of the second capacitor are set to be different from each other.
Further, each of the first central conductor and the second central conductor is constructed by two parallel band-shaped conductors, and the respective distances between the two band-shaped conductors in the first to third central conductors are equally arranged.
REFERENCES:
patent: 4246552 (1981-01-01), Fukasawa et al.
patent: 5994974 (1999-11-01), Makino et al.
patent: 6734753 (2004-05-01), Kawanami et al.
patent: 2002-111319 (2002-04-01), None
Alps Electric Co. ,Ltd.
Jones Stephen E.
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