Wave transmission lines and networks – Coupling networks – Balanced to unbalanced circuits
Reexamination Certificate
1999-07-16
2001-04-03
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Balanced to unbalanced circuits
C333S033000, C333S246000
Reexamination Certificate
active
06211751
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a balun used in telecommunications for feeding electric power to a balanced line from an unbalanced circuit, a power feeder consisting of a microstrip line.
2. Description of Related Art
When using a high frequency band in telecommunications, a microstrip line is often employed as a transmission line for conveying a signal. On the other hand, there is a balanced circuit such as an antenna for transmitting or receiving the signal by radio via space. A balun is used to connect such a balanced circuit with the microstrip line.
FIG. 18
shows a conventional balun. In
FIG. 18
, the reference numeral
1
designates a balanced line; and
2
designates a microstrip center conductor of a microstrip line which constitutes an unbalanced circuit together with a ground plate not shown to transmit a signal. The reference numeral
3
designates a connecting point of the balanced line
1
and microstrip center conductor
2
; and
4
designates an additional line for short-circuiting the balanced line
1
at a position one quarter wavelength apart from the connecting point
3
. The reference numeral
5
designates a grounding terminal for grounding the balanced line
1
at a position half wavelength apart from the connecting point
3
. Because the balanced line
1
is terminated by the short-circuit at one quarter wavelength apart and by the ground at half wavelength apart from the connecting point
3
on the additional line
4
side, a current (unbalanced current) fed from the microstrip center conductor
2
is transformed to a current (balanced current) flowing through the balanced line
1
in opposite directions. With such a structure, the conventional balun must comprise on the balanced line additional circuits such as the quarter-wave transmission line, half-wave transmission line and additional transmission line, and this presents a problem of increasing the dimension of the structure. Furthermore, because the additional circuits are determined in accordance with the wavelength of the signal to be transmitted, and cannot transform signals of other frequencies from an unbalanced to balanced current, a problem arises of restricting the application of the balun fabricated to a particular frequency.
The present invention is implemented to solve the problems. Therefore, an object of the present invention is to provide a compact, rather frequency independent balun.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a balun comprising: a balanced line including a first conductor and a second conductor; a first microstrip center conductor connected to the first conductor of the balanced line; and a second microstrip center conductor connected to the second conductor of the balanced line for supplying the second conductor with a current with a phase opposite to a phase of a current flowing through the first conductor. This makes it possible to reduce the size of the balun because it is unnecessary to provide the additional circuit on the balanced line, and to apply the balun to signals with different frequencies.
Here, the first microstrip center conductor may be formed on one side of a ground plate, and the second microstrip center conductor may be formed on the other side of the ground plate. This makes it possible to simplify the structure of the balun.
The second microstrip center conductor may comprise a delay circuit for delaying an radio wave propagating through the second microstrip center conductor by half wave. This obviates the need for preparing the input signal to the balun with the opposite phase, thereby simplifying an input interface.
The balun may further comprise a feeder for supplying power from the first microstrip center conductor to the second microstrip center conductor through a hole provided in the ground plate. This makes it possible to reduce the input signal to the balun to a single signal.
The balun may further comprise a ground plate of the first microstrip center conductor, a ground plate of the second microstrip center conductor, and a conductor for connecting the two ground plates which are mounted in parallel. This enables the balun to have a space therein.
The first microstrip center conductor and the second microstrip center conductor may be mounted on a side face of a cylindrical groundplate via a dielectric layer. This enables the balun to have a circular space therein.
The balun may further comprise a ground plate on a surface of which the first microstrip center conductor and the second microstrip center conductor are each mounted via a dielectric layer. This makes it possible to form the unbalanced circuit section of the balun on the plane.
The balun may further comprise a ground plate of the first microstrip center conductor, a ground plate of the second microstrip center conductor and a conductor for connecting the two ground plates which are mounted separately on a plane. This makes it possible to form the unbalanced circuit section of the balun on the plane, and to form a space within the balun.
According to a second aspect of the present invention, there is provided a balun comprising a plurality balun components, each of which includes: a balanced line including a first conductor and a second conductor; a first microstrip center conductor connected to the first conductor of the balanced line; and a second microstrip center conductor connected to the second conductor of the balanced line for supplying the second conductor with a current with a phase opposite to a phase of a current flowing through the first conductor, wherein two phases of an radio wave fed to one of the balun components differ from two phases of an radio wave fed to another of the balun components. This makes it possible to rotate the plane of polarization of the radio wave which is radiated from the balanced line.
The one of the balun components may comprise for its two microstrip center conductors two ground plates which are facing to each other, and the another of the balun components may comprise for its two microstrip center conductors two ground plates which are facing to each other and are disposed alternately with the ground plates of the one of the balun components, wherein the four ground plates adjacent to each other may be connected by a conductor. This makes it possible to reduce the size of the individual conductors for connecting the ground plates.
The four microstrip center conductors of the one of the balun components and of the another of the balun components may be connected to one microstrip center conductor and three microstrip center conductors each including a delay line branching from the one microstrip center conductor. This makes it possible to simplify the signal input interface.
According to a third aspect of the present invention, there is provided a balun comprising: a balanced line including a first conductor and a second conductor; a microstrip center conductor connected to the first conductor of the balanced line; and a quarter-wave long conductor plate which is connected at its first edge to a ground plate of the microstrip center conductor and at its second edge to the second conductor of the balanced line. This enables the microstrip center conductor to be reduced to one, thereby improving the productivity.
The conductor plate may connected to the ground plate via a quarter-wave long conductor plate facing the ground plate. This enables the balun to have a space in its unbalanced circuit section.
REFERENCES:
patent: 2107025 (1938-02-01), Buschbeck et al.
patent: 2754484 (1956-07-01), Adams
patent: 5450093 (1995-09-01), Kim
patent: 5471181 (1995-11-01), Park
patent: 2087653 (1982-05-01), None
patent: 63-209201 (1988-08-01), None
Bettendorf Justin P.
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
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