Multibeam antenna reflector

Details Multibeam antenna reflector Multibeam antenna reflector

1999-10-18

2001-01-30

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Wave guide type

Reexamination Certificate

active

06181289

ABSTRACT:

This invention relates to a reflector for a multibeam antenna which can transmit and receive electromagnetic waves in and from different directions.
BACKGROUND OF THE INVENTION
An example of a multibeam antenna is disclosed in, for example, Japanese unexamined patent publication No. HEI 5-191139 published on Jul. 30, 1993. The antenna disclosed in this publication includes two primary radiators disposed to radiate beams to the same point on an offset paraboloidal reflector of the antenna. In this antenna, an axis passing through the aperture center of the paraboloidal reflector and paralleling the parabola axis of the reflector is defined as a beam axis of the paraboloidal reflector. One of the two primary reflectors is located at the focal point of the reflector, and the other radiator is located on the beam axis. The angle between the line passing through the aperture center and the focal point of the reflector and the parabola axis is defined as a tilt angle. The tilt angle is from 1 to 1.4 times a desired beam width.
A reflector meeting the above-stated condition cannot be a versatile reflector, but it can only reflect a beam in or from a specific direction. Recently, satellite communications and satellite broadcasting are common. Accordingly, parabolic antennas which can be used only single satellites are not desirable in manufacturing cost. In addition, in this type of paraboloidal reflectors, aberration due to displaced feeding is minimized under some specific conditions, which results in a large focal-length-to-aperture ratio, F/D, of the paraboloidal reflector.
Therefore, an object of the present invention is to provide a versatile reflector for a multibeam antenna which has a similar size to an ordinary paraboloidal reflector.
SUMMARY OF THE INVENTION
A multibeam antenna according to the present invention includes a reflector surface expressed by at least first and second corrected surface functions combined or merged together. The first corrected surface function can be defined in a coordinate system having a horizontal axis X
1
, a vertical axis Y
1
and an axis Z
1
perpendicular to the plane defined by the X
1
and Y
1
axes, as follows.
z
1
=[−(x
1
2
+y
1
2
)/4(F
1
+g(x
1
, y
1
))]+F
1
where g(x
1
, y
1
) is expressed by k
1
(y
1
+&agr;)+k
2
(|x
1
|+&bgr;), &agr; is a value not smaller than −(of+D) and not greater than (of+D), &bgr; is a value not smaller than −D/2 and not greater than D/2, of is the amount of offset of the reflector which is equal to or greater than 0, D is the diameter of a circle resulting from projecting a given area of the first corrected surface function onto the X
1
-Y
1
plane, F
1
is the focal length of the first corrected surface function, and k
1
and k
2
are coefficients.
The second corrected surface function is defined in a coordinate system having a horizontal axis X
2
, a vertical axis Y
2
and an axis Z
2
perpendicular to the plane defined by the X
2
and Y
2
axes, as follows.
z
2
=[−(x
2
2
+y
2
2
)/4(F
2
+g(x
2
,y
2
))]+F
2
where g(x
2
, y
2
) is expressed by k
1
(y
2
+&agr;)+k
2
(|x
2
|+&bgr;), &agr; is a value not smaller than −(of+D) and not greater than (of+D), &bgr; is a value not smaller than −D/2 and not greater than D/2, of is the amount of offset of the reflector which is equal to or greater than 0, D is the diameter of a circle resulting from projecting a given area of the second corrected surface function onto the X
2
-Y
2
plane, F
2
is the focal length of the second corrected surface function, and k
1
and k
2
are coefficients.
The multibeam antenna reflector is in a combined or merged area expressed by a function formed by weighted-averaging the first and second corrected surface functions with the Z
1
and Z
2
axes disposed in parallel with respective ones of at least two directions from which electromagnetic waves come. The focuses of the first and second corrected surface functions are determined such that the coordinates of the first and second corrected surface functions at the center of the combined area are the same, and that the normals of the first and second corrected surface function at the center of the combined area are in alignment with each other.
It may be that k
2
=0, k
1
<0, and &agr;=−(of+D/2).
It may be that k
1
=0, k
2
>0, and &bgr;=0.
It may be that k
1
=0.
It may be that k
1
=k
2
, &agr;=−(of+D/2), and &bgr;=0.
It may be that k
1
and k
2
each are equal to or greater than −0.2 and equal to or smaller than 0.2.
Additional (m−2) surface functions, where m is a positive integer equal to or greater than three, may be combined with the first and second corrected surface functions by being weighted and averaged with the first and second corrected surface functions. Any additional n-th reflector is expressed by a parabolic function or a corrected surface function in a coordinate system defined by a horizontal axis Xn, a vertical axis Yn and an axis Zn perpendicular to the plane defined by the Xn and Yn axes, where n is a positive integer equal to or greater than 3 and equal to or smaller than m, with the axis Zn disposed along the direction from which an n-th electromagnetic wave comes.


REFERENCES:
patent: 4603334 (1986-07-01), Mizuguchi et al.
patent: 5140337 (1992-08-01), Rappaport
patent: 5283591 (1994-02-01), Delmas
patent: 5790777 (1998-08-01), Luh et al.
patent: 5828344 (1998-10-01), Alder et al.
patent: 5859619 (1999-01-01), Wu et al.
patent: 5913151 (1999-06-01), Lusignan
patent: 5949594 (1999-09-01), Iglseder et al.
patent: 5-191139 (1993-07-01), None

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