Helical antenna

Details Helical antenna Helical antenna

1999-10-12

2001-05-08

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Spiral or helical type

C343S850000

Reexamination Certificate

active

06229498

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a helical antenna used in a mobile wireless (radio) appliance such as a portable telephone.
2. Description of the Related Art
Very recently, mobile communications, e.g., portable telephones are rapidly developed. Not only ground mobile communication systems are available, but also satellite mobile communication systems are expected for practical uses. In such mobile communication terminals, antennas may constitute one of the major important devices, or components.
Now, one example of conventional 4-winding helical antennas will be described with reference to drawings.
FIG. 11
schematically shows an electric power feeding circuit for this conventional helical antenna, and
FIG. 12
is a plan view of the helical antenna to which electric power is supplied by employing the feeding circuit.
An (electric power) feeding circuit
200
is provided with a 3dB-hybrid circuit
201
, a balun circuit
202
, and another balun circuit
203
. These circuits
201
to
203
are mounted, or packaged on the same plane of a mounting board
204
under such a condition that these circuits
201
to
203
are connected via a strip line having a resistance value of 50 &OHgr; to each other.
The hybrid circuit
201
is a circuit for producing an output signal whose output phase is in phase with the input phase thereof (will be defined as a “0° output” hereinafter), and another output signal whose output phase is delayed by 90° from the input phase thereof (will be defined as a “90° output” hereinafter) from a signal which is supplied to the antenna for feeding the electric power. It should be noted that an output signal whose output phase is delayed by 180° from the input phase thereof is defined as a “180° output”, and an output signal whose output phase is delayed by 270° from the input phase thereof is defined as a “270° output”.
The balun circuit
202
contains a signal output unit
205
and another signal output unit
206
. The 0° output derived from the hybrid circuit
201
is entered into the signal output circuit
205
and the signal output circuit
206
, respectively. The signal output units
205
and
206
produce both the 0° output and the 180° output with respect to this input signal of the 0° output as feeding signals, and then output these feeding signals.
The balun circuit
203
contains a signal output unit
207
and another signal output unit
208
. The 90° output derived from the hybrid circuit
201
is entered into the signal output circuit
207
and the signal output circuit
208
, respectively. The signal output units
207
and
208
produce both the 0° output and the 180° output with respect to this input signal of the 90° output as feeding signals, and then output these feeding signals.
As a consequence, the relationship among these feeding signals is established as follows: That is, with respect to the 0° output of the signal output unit
205
, the 180° output derived from the signal output unit
206
is delayed by 180°; the 0° output derived from the signal output unit
207
is delayed by 90°; and the 180° output derived from the signal output unit
208
is delayed by 270°.
In a helical antenna
210
, 4 pieces of antenna elements (not shown) are arranged in a helical form along an outer surface of a hollow cylindrical body
211
.
Each of the antenna elements owns each of signal input units
212
to
215
. The respective signal input units
212
to
215
are arranged in an equi-interval of 90 degrees on an edge portion of the cylindrical body
211
, and also are connected to the respective signal output units
205
to
208
via a power feeding line
216
made of a conductive line with maintaining an individual relationship among them.
As a result, the power feeding signals are supplied from the feeding circuit
200
to the respective antenna elements under such a condition that the phase differences among these feeding signals are made by 90 degrees.
On the other hand, the signal input units
212
to
215
of the respective antenna elements are arranged on an edge surface of the cylindrical body
211
, namely on a circumference within the same plane.
However, the respective signal output units
205
to
208
of the feeding circuit
200
are arranged on the same straight line at an edge portion on the mounting plane of the board
204
.
As a result, the connection distances “a” to “d” between the signal output units
205
to
208
and the signal input units
212
to
215
are made incoincident with each other.
In the case of the antenna arrangement shown in
FIG. 12
, the connection relationship is given by d>a≅b>c. In particular, a distance difference between a connection distance “c” (interval between
207
and
213
) and another connection distance “d” (interval between
208
and
215
) becomes large.
As previously explained, while the connection distances “a” to “d” are made incoincident with each other, if the signal output units
205
to
208
are connected to the signal input units
212
to
215
by way of the feeding lines
216
(
a
) to
216
(
d
), then a large difference is produced in the lengths (electric lengths) of the feeding lines
216
(
a
) to
216
(
d
).
As a consequence, the feeding signals having the phase differences by 90 degrees are not originally supplied to the respective antenna elements. Accordingly, the axial ratio of the radiated circularly-polarized wave is increased. Furthermore, the horizontal plane directivity of this helical antenna is deteriorated. As a result, the signal transmission/reception cannot be carried out in high precision.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is to provide a helical antenna capable of transmitting/receiving a signal in high precision, while increasing precision in a phase difference of electric power feeding to the respective antenna elements.
Other objects, features, and advantages of the present invention may become apparent from the below-mentioned descriptions.
To achieve the above-described objects of the present invention, a helical antenna according to an aspect of the present invention, is featured by comprising: a plurality of antenna elements, each of which antenna elements having a signal input unit for an electric power feeding signal; feeding means having at least plural signal output units corresponding to the number of the signal input units, for outputting the feeding signals from the respective signal output units while giving a predetermined phase difference to the feeding signals; a first holding mechanism for holding the respective signal input units of the antenna elements on the substantially same circumference; a second holding mechanism for holding the respective signal output units of the feeding means on a line which is located perpendicular to a plane where the circumference is positioned, and also which passes through an essential center of the circumference; and a plurality of feeding lines for connecting the respective signal input units of the respective antenna elements to the respective signal output units of the feeding means with maintaining the individual relationship among them.
In the helical antenna, in view of the geometrical aspect, separation distances between one point on the line which passes through the essential center of the above-explained circumference and the arranging positions of the respective signal input units will become constant. As a consequence, in accordance with the present invention, since the signal output units are held on the above-explained line, the lengths of the respective feeding lines can be made substantially equal to each other. Namely, the separation intervals between the signal output units and the signal input units corresponding thereto can be made substantially coincident with each other.


REFERENCES:
patent: 4008479 (1977-02-01), Smith
patent: 5191352 (1993-03-01), Branson
patent: 5986619 (1999-11-01), Grybes et al.

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