Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1999-09-24
2001-03-20
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C333S115000
Reexamination Certificate
active
06204827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to an antenna feeding circuit for an helical antenna, especially, a bifilar, quadrifilar and an octifilar helical antenna. A bifilar helical antenna is a helical antenna furnished with two filaments, a quadrifilar helical antenna is a helical antenna furnished with four filaments and an octifilar helical antenna is a helical antenna furnished with eight filaments.
2. Description of the prior art
Such an antenna feeding circuit is known, for example, from a “¼ turn volute with split sheath balun” shown in FIG. 6 in “Resonant Quadrifilar Helix Antenna” disclosed in “Microwave Journal”, December, 1970, p49-53.
FIG. 12
is a schematic perspective view of an antenna feeding circuit in the prior art, more specifically, it shows a ¼ turn volute with split sheath balun disclosed in the article. In the figure, reference numerals
61
,
62
denote, respectively, a first helical antenna element and a second helical antenna element. Reference numerals
63
,
64
denote, respectively, a coaxial cable for feeding the helical antenna and a ¼ wavelength slit disposed on the outer conductor of the coaxial cable
63
. Reference numeral
65
denotes an impedance converter disposed on the inner conductor of the coaxial cable
63
. Electric power is fed to the first and second helical antenna elements
61
,
62
from an electric power feeding point
66
.
Regarding the function, the first and second helical antenna elements
61
,
62
can be assumed to be balanced lines, similar to a pair of parallel two lines. When unbalanced lines, for example, such as a coaxial cable, are connected to a helical antenna, a balance-unbalance converter is required between the helical antenna elements
61
,
62
and the coaxial cable. Therefore, a balun, constituted by the coaxial cable
63
, the ¼ wavelength slit
64
and the impedance converter
65
, is disposed as a balance-unbalance converter. Another function of this balun is to cancel out an inutile current, which appears when a balanced line is connected to an unbalanced line.
Japanese Patent Application 63-30006-A discloses another antenna feeding circuit, which comprises a ¼ wavelength slit disposed on the outer conductor of a coaxial cable. The antenna comprises two sets of antenna elements, having an equal pitch angle, and each set of antenna elements is connected to one of two connecting portions of a connecting piece. The structure of this antenna feeding circuit facilitates the assembling of the antenna, and improves the preciseness of dimensions of the components of the antenna feeding circuit.
The antenna feeding circuits in the prior arts have following drawbacks due to such structures:
A balun is of a rather long dimension, i.e., ¼ wavelength, in the longitudinal direction of an antenna;
The structure is rather complicated, as for example, when a coaxial structure of the antenna portion and the feeding circuit portion is employed to shorten the total length of the system including the length of the antenna portion.
SUMMARY OF THE INVENTION
An object of the present invention is to propose an antenna feeding circuit, which can eliminate such drawbacks in the prior art.
Another object of the present invention is to propose an antenna feeding circuit, which requires no balance-unbalance converter (balun), such as used in the prior art, and has a simple structure.
The objects are attained by the antenna feeding circuit, according to the present invention, comprising:
an inner conductor disposed on the inner surface of a cylindrical body;
a pair of band conductors disposed on the outer surface of the cylindrical body at a position symmetrical with respect to the axis of the cylinder so as to be parallel with the longitudinal direction of the cylinder;
a 180 degree distributor, connected to an end of each of the band conductors, for supplying electric power to each of the band conductors, so that the phase difference between the currents in the band conductors is 180 degrees; and
a helical antenna, each element of the helical antenna corresponds to one of the band conductor and is connected to the other end of the band conductors.
In an embodiment of the antenna feeding circuit according to the present invention, the band conductors comprise an impedance matching circuit.
In an embodiment of the antenna feeding circuit according to the present invention, the band conductors comprise a capacitor element as an impedance matching circuit.
In an embodiment of the antenna feeding circuit according to the present invention, the band conductors comprise a meander line as an impedance matching circuit.
In an embodiment of the antenna feeding circuit according to the present invention, the band conductors comprise a short stub as an impedance matching circuit.
In an embodiment of the antenna feeding circuit according to the present invention, the 180 degree distributor comprises:
a T-branching circuit having an input terminal and a pair of output terminals, which are T-branched from the input terminal; and
a delay line connected to either of the output terminals, the electric length of the delay line is identical to a half of the wavelength at the frequency in use.
In an embodiment of the antenna feeding circuit according to the present invention, the 180 degree distributor comprises: a T-branching circuit comprising a first micro-strips line as an input terminal and a second and third micro-strips lines as output terminals, which are T-branched from the first micro-strips line; and a slot disposed on the substrate of the T-branching circuit so as to be perpendicular to the first micro-strips line, the length of the slot is substantially a half of the wavelength of the frequency in use; wherein the first micro-strips line is grounded to the substrate at a point in the opposite side to the input side of the first micro-strips line with respect to the slot; the second micro-strips line is disposed at the same side to the input side of the first micro-strips line and is grounded to the substrate at a point in the opposite side to the input side of the first micro-strips line with respect to the slot; the third micro-strips line is disposed at the opposite side to the input side of the first micro-strips line and is grounded to the substrate at a point in the same side to the input side of the first micro-strips line with respect to the slot.
The antenna feeding circuit according to an embodiment of the present invention comprises: an inner conductor disposed on the inner surface of a cylindrical body; first and second pairs of band conductors disposed on the outer surface of the cylindrical body at a position symmetrical with respect to the axis of the cylinder so as to be parallel with the longitudinal direction of the cylinder; first and second 180 degree distributors connected to an end of a band conductor in each pair of the band conductors, for supplying electric powers to each of the band conductors, so that the phase difference between the currents in the band conductors in each group of the band conductors is 180 degrees; a 90 degree distributor connected to the first and second 180 degree distributor, for supplying electric power to each of the first and second 180 degree distributors so that the phase difference between the input electric power to the first and second 180 degree distributors is 90 degrees; and a quadrifilar helical antenna, each element of the quadrifilar helical antenna corresponds to one of the band conductor and is connected to the other end of the band conductor.
The antenna feeding circuit according to an embodiment of the present invention comprises: an inner conductor disposed on the inner surface of a cylindrical body; first to fourth pairs of band conductors disposed on the outer surface of the cylindrical body at a position symmetrical with respect to the axis of the cylinder so as to be parallel with the longitudinal direction of the cylinder; first to fourth 180 degree distributors, connected to an end o
Chiba Isamu
Endo Tsutomu
Fukasawa Toru
Miyazaki Moriyasu
Clinger James
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
Wong Don
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