JPH05199033A - Multi-beam antenna system - Google Patents

Abstract

PURPOSE:To provide the multi-beam antenna with a high gain at defocus feeding by selecting an aperture face amplitude distribution on an axis of defocal point to be a tapered distribution and an aperture face amplitude distribution on an axis orthogonal to the defocal axis to be a distribution close to the uniformity. CONSTITUTION:(x, y) is a orthogonal coordinate system in which a center 10 of a main reflecting mirror aperture face 9 is taken as the origin 10. When a center of a beam radiating from each of primary radiators 3, 4 is resident on an x-axis or its vicinity, an amplitude distribution formed by an electric field radiating from primary radiators 3, 4 placed to focal points 5, 6 of the mirror face system at a main reflection mirror aperture face 9 is a distribution with a low level around the aperture face edge within a plane of y=0 deg.. Moreover, the mirror face is corrected so as to have almost uniform distribution within a plane of x=0 deg.. Thus, the multi-beam antenna with a high gain is formed at defocal feeding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflector antenna technique, and more particularly to a technique for constructing a multi-beam earth station antenna for simultaneously accessing a plurality of communication satellites.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIG. 4A and 4B are diagrams showing a configuration of a conventional antenna and an example of an amplitude distribution on an aperture plane, where FIG. 4A shows the configuration of the antenna and FIG. 4B shows an amplitude distribution on the aperture plane.
As shown in the figure, this antenna is composed of a main reflecting mirror 1, a sub-reflecting mirror 2, and primary radiators 3 and 4. Also,
Reference numerals 5 and 6 are the phase centers of the primary radiators 3 and 4, respectively, and 5 is the focal point of the mirror surface system. Furthermore, 7 and 8 are primary radiators 3,
4 shows the traveling direction of the central ray radiated from 4
Represents the aperture surface of the main reflecting mirror, and 10 represents the center of the aperture. Then, the ray 7 passes through the center 10 of the opening.

In order to obtain a high-gain beam in the antenna design, the primary reflector 3 and the sub-reflecting mirror 2 are modified by focusing on the focused primary radiator 3. In ordinary mirror surface modification, when the target aperture distribution is (1-r ² ) ^p , the following “Equation 1” is used.

[0004]

[Equation 1]

This expression means that the electric power of the radio wave radiated by the horn in a certain angle range of 0 ° to θ is equal to the electric power of the radius 0 to r of the opening surface, which is a basic expression for mirror surface modification. There is one. However, r is the normalized radius of the opening surface,
It is an arbitrary value from 0 to 1. Further, p is an arbitrary real number, for example, if p = 0, the distribution is uniform, and as p is increased, the distribution is tapered at the end of the opening surface. θ
Is the angle from the central axis of the beam emitted from the horn,
θ ₀ represents the angle of view of the reflecting mirror, and H (θ) represents the radiation pattern of the horn.

The above "Formula 1" can be solved analytically or numerically, and r is determined for a certain θ. With this formula, the law of reflection and the law of constant optical path length, the reflection mirror surface coordinates can be determined. FIG. 4B shows a conceptual diagram of the amplitude distribution on the aperture surface 9 obtained as a result of mirror surface modification. Equal amplitude curve 1
It can be seen that 2 is closer to the periphery of the opening surface, and a nearly uniform axisymmetric distribution is realized.

In order to evaluate the characteristics of the multi-beam antenna, an example of the calculation result of the peak gain when feeding the defocused light is shown in FIG. 5 as a characteristic diagram. In the figure, the horizontal axis represents the angle with the z-axis direction being 0 °, and the vertical axis represents the antenna peak absolute gain value in dB. Also, assume that the center of the radiation beam is on the x-axis.

Such beam arrangements are found, for example, in the design of multi-beam earth station antennas that simultaneously access multiple geostationary satellites in substantially linear satellite orbits. The curve 13 is an example of the calculation result, and the mirror surface parameter is determined on the assumption that it is put to practical use. Main calculation parameters are: main reflector aperture diameter 4.2m, frequency 6GHz
And The aperture surface distribution which is the design target is (1-r ² ) ^p , and P = 0.4 is given here.

FIG. 6 is a characteristic diagram showing an example of the calculation result of the amplitude distribution on the aperture plane at the time of focus feeding. In the figure,
The horizontal axis represents the normalized radius and the vertical axis represents the amplitude level, and the level at the center of the aperture is 0 dB. The level at the edge of the opening surface is about -10 dB with respect to the center of the opening. The gain during focus feeding shows a value of 80% or more in aperture efficiency.

However, as the defocus amount increases,
The gain drops sharply. For example, when accessing two satellites that are 4.5 ° apart, the gain deteriorates by 2 dB or more as compared with when the defocus amount is 0 °. The reason for this is that, as can be seen from FIG. 6, the irradiation level around the edge of the main reflecting mirror opening surface is high, the axially symmetrical distribution of the main reflecting mirror opening surface is distorted during defocus feeding, and the power around the mirror surface edge is mainly reflected. It is thought that it leaks out of the mirror.

[0011]

[Problems to be Solved by the Invention] As described above,
An antenna with axisymmetric high efficiency aperture plane amplitude distribution has a problem that the gain drop is large when feeding defocused light. The present invention has been made to solve this problem, and an object thereof is to reduce the decrease in gain during defocusing power feeding.

[0012]

According to the invention, the above objects are achieved by the means recited in the claims. That is, according to the invention of claim 1, in a multi-beam antenna including a main reflecting mirror, a sub-reflecting mirror, and a plurality of primary radiators, an orthogonal coordinate system whose origin is the center O of the opening surface of the main reflecting mirror is defined as xy. , When the center of the beam radiated from each primary radiator is on or near the x-axis, the amplitude distribution created by the electric field radiated from the primary radiator placed at the focal point of the specular system on the aperture surface of the main reflector is , Y = 0 °, and the level around the edge of the aperture surface is low, and the mirror surface is modified to have a substantially uniform distribution in the x = 0 ° plane. The invention of (1) is a multi-beam antenna device in which a plurality of mirror surfaces are provided between the sub-reflecting mirror and the primary radiator in the antenna having the above-mentioned configuration. Less than,
The operation and the like of the present invention will be described based on examples.

[0013]

FIG. 1 is a diagram showing an embodiment of the present invention.
(A) shows the antenna configuration, and (b) shows the amplitude distribution on the aperture plane. A characteristic feature of the amplitude distribution is that it is sparse on the x axis and dense on the y axis, as indicated by numeral 11 in FIG. Such a distribution is
In (Equation 1), (1-r ² ) ^{P v} cos ² φ + (1-r ² ) ^Ph sin ² φ may be used instead of the target aperture distribution (1-r ² ) ^p . However, φ is a deflection angle with the y axis set to 0 °. Therefore, at φ = 0 ° (in the vertical plane), (1-
r ² ) ^{P v} , φ = 90 ° (in the horizontal plane) (1-r ² )
^A distribution of ^Ph is obtained.

The operation of this embodiment will be described below.
FIG. 2 shows an example of the calculation result of the gain at the time of defocusing power feeding, and FIG. 3 shows an example of the calculation result of the amplitude distribution of the aperture plane at the time of focusing power feeding as a characteristic diagram. In the same calculation, the main calculation parameters are
Same as Fig. 4, main reflector aperture diameter 4.2m, frequency 6GH
z, Ph = 2.0 and Pv = 0.4.

Since the aperture distribution in the horizontal plane is tapered, the gain at the time of focus feeding is lower than that in FIG. However, as can be seen from FIG. 3 (a), since the specular edge level on the opening surface at the time of focus feeding in the horizontal plane is as small as −30 dB compared to the center of the opening, the leakage power on the opening surface at the time of defocusing feeding is high. The level is small and the gain deterioration is small. Thereby, for example, the gain at the defocus amount of 2.25 ° becomes higher than that in FIG.

As described above, the aperture plane amplitude distribution along the axis of defocus (in the description, the x-axis) is tapered,
If the aperture plane amplitude distribution on the axis orthogonal to it (the y axis in the description) is made to be a nearly uniform distribution, a multi-beam antenna with high gain can be realized at the time of defocus feeding.

[0017]

As described above, according to the present invention, there is an advantage that a multi-beam antenna having high gain can be realized at the time of defocusing power feeding.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of a result of calculation of gain when defocusing power is fed.

FIG. 3 is a characteristic diagram showing an example of a calculation result of an amplitude distribution of an aperture plane at the time of focus power feeding.

FIG. 4 is a diagram showing a configuration of a conventional antenna and an example of amplitude distribution on an aperture plane.

FIG. 5 is a characteristic diagram showing an example of a calculation result of peak gain during defocusing power feeding.

FIG. 6 is a characteristic diagram showing an example of the calculation result of the amplitude distribution on the aperture surface at the time of focus power feeding.

[Explanation of symbols]

 1 Main Reflector 2 Sub Reflector 3,4 Primary Radiator 5,6 Phase Center of Primary Radiator 7,8 Direction of Center Ray 9 Main Reflector Aperture Surface 10 Aperture Center 11,12 Equal Amplitude Curve 13 Calculated Characteristics curve

Claims (2)

[Claims] 1. In a multi-beam antenna comprising a main reflecting mirror, a sub-reflecting mirror, and a plurality of primary radiators, an orthogonal coordinate system whose origin is the center O of the main reflecting mirror opening surface is x-
When y is the center of the beam emitted from each primary radiator and is on or near the x-axis, the amplitude of the electric field emitted from the primary radiator placed at the focal point of the specular system at the aperture of the main reflector. A multi-beam antenna device, wherein the distribution is mirror-modified so that the level around the edge of the aperture plane is low in the y = 0 ° plane and the distribution is almost uniform in the x = 0 ° plane. 2. The multi-beam antenna device according to claim 1, wherein a plurality of mirror surfaces are provided between the sub-reflecting mirror and the primary radiator.