Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2003-03-12
2004-12-07
Lam, Tuan T. (Department: 2816)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06828871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nonreciprocal circuit devices utilizing the Faraday effect.
2. Description of the Related Art
The main portion of a known nonreciprocal circuit device is shown in
FIG. 8. A
disc-like magnetic core
21
formed of ferrite, such as yttrium-iron-garnet (YIG), is disposed in a DC magnetic field generated by a permanent magnet (not shown), and the top surface of the magnetic core
21
is perpendicular to the direction of the DC magnetic field. Three central conductors
22
,
23
, and
24
are placed on the top surface of the magnetic core
21
, and are held so that they overlap with each other at regular intervals (120°) substantially at the center of the magnetic core
21
while being insulated from each other. The lengths of the three central conductors
22
,
23
, and
24
are substantially the same, and thus, the inductances are also substantially equal.
The central conductors
22
,
23
, and
24
include two strip-like conductor portions
22
a
and
22
b
,
23
a
and
23
b
, and
24
a
and
24
b
, respectively, opposing each other. One end of the central conductor
22
serves as an input/output terminal
22
c
, and the other end thereof is used as a ground terminal
22
c
; one end of the central conductor
23
serves as an input/output terminal
23
c
, and the other end thereof is used as a ground terminal
23
c
; and one end of the central conductor
24
serves as an input/output terminal
24
c
, and the other end thereof is used as a ground terminal
24
d
. The input/output terminals
22
c
,
23
c
, and
24
c
are connected to corresponding circuits (not shown), and are grounded via matching termination capacitors
25
,
26
, and
27
, respectively, which have equal capacitances. The ground terminals
22
d
,
23
d
, and
24
d
are connected to corresponding grounded casings (not shown).
The central conductor
22
and the termination capacitor
25
form a resonance circuit. Similarly, the central conductor
23
and the termination capacitor
26
form a resonance circuit, and the central conductor
24
and the termination capacitor
27
form a resonance circuit. The resonant frequencies of the resonance circuits are set by the corresponding termination capacitors
25
,
26
, and
27
so that they become equal to the frequency of an input signal. The central conductors
22
,
23
, and
24
are coupled to each other, and then, a double-tuned circuit is formed, for example, between the input/output terminals
22
c
and
23
c
. Similarly, double-tuned circuits are also formed between the input/output terminals
23
c
and
24
c
and between the input/output terminals
24
c
and
22
c.
In the above-described configuration, due to the Faraday effect, the following phenomenon occurs. A signal input into the input/output terminal
22
c
of the central conductor
22
is output to the input/output terminal
23
c
of the central conductor
23
, which is displaced clockwise from the input/output terminal
22
c
by 120°. A signal input into the input/output terminal
23
c
of the central conductor
23
is output to the input/output terminal
24
c
of the central conductor
24
, which is displaced clockwise from the input/output terminal
23
c
by 120°. A signal input into the input/output terminal
24
c
of the central conductor
24
is output to the input/output terminal
22
c
of the central conductor
22
.
The central conductors
22
,
23
, and
24
overlap with each other on the magnetic core
21
such that they are extremely close to each other. Accordingly, the above-described double-tuned circuits are closely coupled to each other, and the transmission characteristic, for example, from the input/output terminal
22
c
to the input/output terminal
23
c
exhibits a double peak response, as shown in
FIG. 9
, and the insertion loss becomes large at frequency F
0
. The return loss indicating the input impedance or the output impedance at the input/output terminal also exhibits a double peak response, and becomes low (small) at frequency F
0
. For allowing the double-tuned circuits to critically coupled to each other, the central conductors can be separated by vertically displacing them from each other. It is difficult, however, to physically change the positional relationship among the central conductors in the vertical direction.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to decrease loss at a signal frequency and to increase return loss at input/output terminals by ensuring a required transmission band for input/output signals.
In order to achieve the above object, the present invention provides a nonreciprocal circuit device including: a planar magnetic core disposed in a DC magnetic field, a top surface of the magnetic core being perpendicular to the direction of the DC magnetic field; and three central conductors disposed to overlap with each other substantially at a central portion of the top surface of the magnetic core, one end of each of the three central conductors being used as an input/output terminal, and the other end thereof being used as a ground terminal. The inductance per unit length from the central portion to the ground terminal of each of the three central conductors is set to be smaller than that from the central portion to the input/output terminal of each of the three central conductors.
With this configuration, the inductance from the central portion to the ground terminal becomes relatively smaller than that from the central portion to the input/output terminal. Accordingly, the transmission characteristic between the input/output terminals exhibits substantially a single peak response rather than a double peak response, thereby decreasing the transmission loss. The return loss also exhibits substantially a single peak response, and the impedance matching with another circuit connected to the nonreciprocal circuit device can be provided.
Each of the three central conductors may include two strip-like conductor portions opposing each other with an equal spacing therebetween, and a short-circuiting strip for connecting the two strip-like conductor portions may be provided between the central portion and the ground terminal. With this arrangement, the inductance from the central portion to the ground terminal becomes relatively smaller than that from the central portion to the input/output terminal.
Alternatively, each of the three central conductors may include two strip-like conductor portions opposing each other, and the width of each of the strip-like conductor portions from the central portion to the ground terminal may be set to be greater than that from the central portion to the input/output terminal. With this arrangement, the inductance from the central portion to the ground terminal becomes relatively smaller than that from the central portion to the input/output terminal. Additionally, a greater width of the strip-like conductor portions toward the ground terminal decreases the current loss.
Alternatively, each of the three central conductors may include two strip-like conductor portions opposing each other, and the spacing between the two strip-like conductor portions from the central portion to the ground terminal may be set to be greater than that from the central portion to the input/output terminal. With this arrangement, the inductance from the central portion to the ground terminal becomes relatively smaller than that from the central portion to the input/output terminal.
In the above-mentioned modification, the width of each of the strip-like conductor portions from the central portion to the ground terminal may be set to be greater than that from the central portion to the input/output terminal. With this arrangement, the inductance from the central portion to the ground terminal relatively becomes much smaller than that from the central portion to the input/output terminal. Additionally, a greater width of the strip-like conductor portions toward the ground terminal decreases the current loss.
REFERENCES:
patent: 35
Lam Tuan T.
Nguyen Hiep
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