Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2000-02-22
2001-06-26
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C343S713000, C342S371000, C342S375000
Reexamination Certificate
active
06252560
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-11-43802 filed on Feb. 22, 1999, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multibeam antenna used in a wireless communication system, more particularly to a multibeam antenna which includes auxiliary antenna elements disposed next to main antenna elements and to an antenna system in which such an antenna is used.
2. Description of Related Art
An antenna for forming multiple beams by supplying power thereto from a Butler-matrix feeder circuit is known hitherto. The Butler-matrix feeder is proposed and described in ELECTRONIC DESIGN, VOL. 9, pp. 170-173, issued April, 1961 under a title “Beam-forming matrix simplifies design of electronically scanned antennas.” The Butler-matrix feeder has 2
n
input/output ports and composed of hybrid circuits and phase shifters both connected via transmission lines. 2
n
antenna elements are connected to output ports of the Butler-matrix feeder and constitute an antenna array which forms 2
n
beams.
FIG. 19
shows a multibeam antenna using the Butler-matrix feeder (referred to as a Butler-matrix antenna). A Butler-matrix feeder circuit
2
has input ports
1
a
-
1
d,
and antenna elements
3
a
-
3
d
constituting an antenna array are connected to the Butler-matrix feeder circuit
2
. The Butler-matrix feeder circuit
2
is used for forming multiple beams each having a different radiation pattern, the number of which is equal to the number of input ports. The feeder circuit
2
includes first stage hybrid circuits
21
a,
21
b,
constant-phase shifters
22
a,
22
b,
and second stage hybrid circuits
23
a,
23
b.
Electric power supplied from the input ports
1
a
-
1
d
to the feeder circuit
2
is converted into outputs having a predetermined phase difference and is fed to four antenna elements
3
a
-
3
d
which in turn form four beams to be transmitted to directions different from one another. The input ports
1
a
-
1
d
function as output ports when outside radio waves are received by the antenna elements
3
a
-
3
d.
An example of a multibeam antenna circuit layout is shown in FIG.
20
. In this example, micro-strip lines are used as transmission lines, and linearly polarized patch antennas are used as the antenna elements
3
a
-
3
d.
The transmission lines are formed on both the front and rear surfaces of a three-layer substrate
4
, and a ground plate is embedded in the substrate
4
. The transmission lines on the front surface are connected to those on the rear surface via through-holes
24
formed on the substrate
4
. More particularly, the first stage hybrid circuits
21
a,
21
b
are formed on the front surface and the second stage hybrid circuits
22
a,
22
b
on the rear surface. Each antenna element
3
a
-
3
d
is connected to the second stage hybrid circuits
22
a,
22
b
via a respective transmission line, and each second stage hybrid circuit
22
a,
22
b
is connected to each first stage hybrid circuit
21
a,
21
b
with respective two transmission lines as shown in
FIG. 20
(solid lines are formed on the front surface and the dotted lines on the rear surface). There are eight connecting lines altogether, and one through-hole
24
corresponds to each connecting line. In this arrangement, phase difference due to the through holes
24
can be neglected.
Simulation results as to the circuit shown in
FIG. 20
are shown in the graph of
FIG. 21
, assuming that a distance between neighboring two antenna elements is one half of the wavelength. The radiation pattern of four beams, i.e., relative power intensity versus beam angle, is plotted together with sidelobes. In the Butler-matrix antenna, the power fed from the input ports is distributed to the output ports with the same amplitude and a predetermined phase difference. Accordingly, the beam shapes formed by the antenna are solely determined depending on the distance among antenna elements, and formation of large sidelobes is unavoidable, as generally known. Moreover, the number of the antenna elements is limited to the numbers which are in units of 2
n
, i.e., 2, 4, 8, 16, etc. Therefore, it is difficult to arbitrarily increase the antenna gain.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved multibeam antenna in which the sidelobes are reduced and an arbitrary gain increase is readily available. Another object of the present invention is to provide antenna systems using such an improved antenna in wireless communication.
The multibeam antenna according to the present invention is composed of a Butler-matrix feeder circuit and an antenna array that includes main antenna elements and auxiliary antenna elements. In the antenna array, 2
n
main antenna elements are located in the middle, and a group of auxiliary antennas consisting of 2
n
or less auxiliary antenna elements is located at either one or both sides of the main antenna elements.
Antenna power is supplied to the antenna array from the Butler-matrix feeder circuit. All the main and auxiliary antenna elements are arranged in line with equal intervals therebetween. A phase of power supplied to one of the main antenna elements is shifted by 180-degree, and the phase-shifted power is fed to one of the auxiliary antenna elements that is located 2
n
antenna element apart from that main antenna element. A phase difference between two neighboring antenna elements is made all equal throughout the antenna array. The antenna power is distributed to all the antenna elements, so that higher power is fed to the elements located in the center portion of the array, and lower power to the elements located remote from the center portion. All the multiple beams formed by the antenna array are used in wireless communication, or one or more beams may be selectively used.
For example, four main antenna elements are placed in line in the middle portion of the array, and one each auxiliary antenna element is placed at both sides of the main antenna elements. All the elements arranged in line are sequentially numbered from the left to the right, i.e., No. 1 to No. 6. The phase of the power supplied to No. 5 main antenna element is shifted by 180-degree, and the phase-shifted power is supplied to No. 1 auxiliary antenna element. Similarly, the power supplied to No. 2 main antenna element is distributed to No. 6 auxiliary antenna element after the phase of the power is shifted by 180-degree. The power is distributed to each antenna element with ratios, for example, 0.1, 0.9, 1.0, 1.0, 0.9 and 0.1 from the left to the right.
According to the present invention, sidelobes of the multiple beams formed by the antenna array are reduced, and the beam directivity is improved. Moreover, the antenna gain can be improved by properly arranging the antenna elements and properly setting the power distribution among the antenna elements.
The multibeam antenna of the present invention can be used in various antenna systems in wireless communication. For example, three multibeam antennas may be placed around a triangular or cylindrical pillar so that the multiple beams are transmitted to all directions to cover 360-degree communication. The multibeam antenna may be used in mobile communication by using it as an on-board antenna mounted on an automobile, or using it as an antenna located over a road or a highway. In the mobile communication system, the multibeam antenna may be used both as an one-board antenna and as a communication terminal antenna.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.
REFERENCES:
patent: 4228436 (1980-10-01), Dufort
patent: 4672378 (1987-06-01), Drabowitch et al.
patent: 4837580 (1989-06-01), Frazita
patent: 5233358 (1993-0
Saito Toshiya
Tanaka Makoto
Denso Corporation
Fish & Richardson P.C.
Phan Tho
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