JPH042208A - Multi-beam antenna - Google Patents

Abstract

PURPOSE:To improve the aperture efficiency and the cross polarized wave characteristic by reflecting a radio wave reflected from plural primary radiators respectively in relevant auxiliary reflecting mirror, a sub reflecting mirror and a main reflecting mirror sequentially and radiating the radio wave to plural different directions. CONSTITUTION:Auxiliary reflecting mirrors 31-34 are arranged among primary radiators 41-44 as feeding points Pf2-Pf4 and sub reflecting mirrors 21-24 corresponding to beams 1-4. The a light radiating from a feeding point Pf1 is sequentially reflected in the auxiliary reflecting mirror 31, the sub reflecting mirror 21 and the main reflecting mirror 1 and collimated as the beam 1. Similarly the light radiating from the feeding points Pf2-Pf4 is reflected respectively in the auxiliary reflecting mirrors 32-34, the sub reflecting mirrors 21-23 and the main reflecting mirror 1 and collimated as the beams 2-4. Thus, the aperture efficiency and the cross polarized wave characteristic are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-beam antenna that enables simultaneous communication with a plurality of satellites in a geosynchronous orbit using one antenna.

[Conventional technology]

In a conventional multi-beam antenna, for example, as shown in FIG. 10, one main reflector 1 is shared by multiple (four in this case) beams, and one sub-reflector 21 to 24 is used for each beam.
There are some that correspond to each other.

The main reflecting mirror 1 is a quadratic curved surface such as a paraboloid or a torus, and the shapes of the sub-reflecting mirrors 21 to 24 are adjusted so that the optical path length from the feeding point of each beam to the aperture surface is constant.

Therefore, the phases on the aperture plane, which is a plane perpendicular to each beam, are uniformly aligned.

Here, the optical path length means the feeding points Pfl, PfZ,
P fff This is the total distance of the light rays emitted from Pf4 being reflected by the sub-reflecting mirrors 21, 22, 23, and 24 and the main reflecting mirror 1 and reaching each aperture surface.

[Problem to be solved by the invention]

However, in the conventional multi-beam antenna described above, when calculating the shape of the sub-reflector, the correspondence between the radiation pattern of the primary radiator and the power distribution at the aperture plane is not taken into consideration. Distribution cannot be controlled.

As a result, mapping distortion as shown in FIG. 9 occurs between the two.

The mapping referred to here is an image formed on a virtual plane in front of the power feeding section when a group of concentric circles at the aperture plane enters the main reflecting mirror 1 as parallel rays.

If this mapping is distorted, the power on the antenna aperture will be biased, which will reduce the aperture efficiency, and even if the polarization direction of the -order radiator is constant, the polarization direction at the aperture plane will not be constant.
Cross polarization characteristics deteriorate.

An object of the present invention is to provide a multi-beam antenna that improves aperture efficiency and cross-polarization characteristics.

(Means for Solving the Problems) The multi-beam antenna of the present invention is provided between a plurality of sub-reflectors arranged opposite to one main reflector and a plurality of primary radiators each of which emits radio waves. An auxiliary reflector is provided at each of the auxiliary reflectors, and the radio waves emitted from each of the plurality of primary radiators are sequentially reflected by the corresponding auxiliary reflector, sub-reflector, and main reflector, and then radiated in multiple different directions. It is configured so that

Here, the main reflecting mirror is constituted by a part of a paraboloid of revolution.

In addition, the sub-reflector is a first reflector that is formed by a correspondence relationship between the radiation power pattern of the primary radiator and the power distribution on the aperture surface of the main reflector.
and a second condition in which the distances from the phase center of the primary radiator to the plane perpendicular to the radio wave emission direction after being reflected by the auxiliary reflector, sub-reflector, and main reflector are equal to each other. It is obtained by solving the radial differential equation of the circumferential differential equation and the radial differential equation derived from the second condition and the third condition that the reflection of the light beam on the auxiliary reflector follows Snell's law. Composed of curved surfaces.

Furthermore, when a ray of light parallel to the radiation direction of the radio wave is incident on the auxiliary reflector, the ray is reflected one after another by the main reflector, the sub-reflector, and the auxiliary reflector, and reaches the phase center of the primary radiator. It is composed of curved surfaces determined so that the distances are equal for each ray.

[Effect]

According to the present invention, by adding an auxiliary reflecting mirror, the aperture efficiency and cross-polarization characteristics of the multi-beam antenna are improved.

In addition, by configuring the curved surfaces of the main reflector, sub-reflector, and auxiliary reflector to satisfy their respective conditions, the aperture efficiency and cross-polarization characteristics are improved, and the power distribution at the antenna aperture is improved. Make it controllable.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic perspective view of an embodiment of the present invention, showing an example in which the present invention is applied to a four-beam multi-beam antenna. In the figure, 1 is the main reflecting mirror, which is composed of an offset paraboloid, and the beams 1, 2,
It is shared by 3.4. Sub-reflector 21.22, 23.24 corresponding to beams 1, 2, 3.4 and feeding point P fl of each beam.

P f3. Primary radiators 41, 42 as P fl
, 43° and 44, there are auxiliary reflecting mirrors 31 and 32, respectively.
゜33.34 is installed. Note that the sub-reflector 21
~ 24 and auxiliary reflectors 31 to 34 are used for beams 1 to 4, respectively.
It is constructed as a mirror surface adjusted according to the direction of the surface.

In this multi-beam antenna, for example, the feeding point P
The light beam emitted from fl is transmitted through the auxiliary reflector 31° and the sub-reflector 21. It is sequentially reflected by the main reflecting mirror 1 and becomes a parallel light beam as a beam 1. Similarly, the feed point PfZ+ PF3.
The light beams emitted from PF3 are each auxiliary reflector 3.
2, 33, 34, the sub-reflector 2122.23, and the main reflector 1, resulting in a parallel configuration as beams 2, 3.4.

Here, the shapes of the sub-reflector and the auxiliary reflector are determined by the following procedure.

First, in the first step, the path of the central axis of the ray group is determined. That is, the direction of the beam, the position and orientation of the feeding point and the primary radiator at L7, and the positions of the centers of the sub-reflector and the auxiliary reflector are determined.

In the second step, the shape of the sub-reflector is determined by solving a differential equation obtained based on the law of conservation of energy, Snell's law, and the constant optical path length condition in the radial direction from the center of the mirror surface.

In the third step, the shape of the auxiliary reflector is determined from the shape of the auxiliary reflector obtained in the second step and the constant optical path length condition.

Hereinafter, specific calculations for one beam will be sequentially explained.

FIG. 2 is a diagram showing the calculation method. The light beam emitted from the feeding point P of the primary radiator 4 reaches the point PL on the auxiliary reflector 3,
It is reflected at a point PS on the sub-reflector 2 and a point P on the main reflector 1, and reaches a point P1 on the aperture surface 5. The aperture plane 5 is a plane perpendicular to the beam direction, and here points P,
The direction in which the empty point P is viewed is the beam direction.

Also, point P,. ,P. ,Pl. ,P. are the auxiliary reflectors 3 and 3, respectively. Secondary reflector 2. Main reflector 1. This is the center of the aperture surface 5, and shows the path followed by the central axis of the group of light rays emitted from the feeding point Pf.

In addition, in the following calculation, from point P, point Pt2, point Pt, point 262, point P5, point 2. ．． 9 The unit vectors of the rays from point P1 to point P1 are each σ.

ξ, shi, μ, and points P, P, and two points PtP, between.

The distance between points P and P is r.

Let them be u, v, and t.

FIG. 3 shows how to determine the actual angle of the direction (δ7.γf) of the primary radiator 4. FIG. 3 shows the relationship between the local coordinate system x'y'z' and the principal coordinate system xyz in the power feeding section, and the Z'-axis positive direction coincides with the direction of the primary radiator.

From the primary radiator, the opening angle θ is as shown in FIG. A group of light rays is emitted within the cone of. The direction of each ray in the ray group is represented by (θ, ψ) as shown in the figure.

Similarly, FIG. 5 shows the relationship between the local coordinate system X"yz" and the principal coordinate system xyz on the aperture plane.

The beam direction (δa, T,) coincides with the 2″-axis positive direction in the local coordinate system.

FIG. 6 shows a local coordinate system at the aperture plane 5, and the cross section of a group of light rays is drawn as a circle. Opening angle θ at the feed section. The light rays within the cone reach a circle with a diameter on the aperture surface 5 after being reflected three times.

The direction of each ray on the aperture plane 5 is perpendicular to the aperture plane 5,
It coincides with the positive direction of the 2″ axis, and the position where each ray in the ray group passes on the aperture surface 5 is as shown in the same figure (p, tI
/).

Now, the first step in this calculation method is to determine the central axis of the ray. For this path, first (a) determine the desired beam direction (δm, Tm);

On the other hand, (b) the position Pt (xf, yr, Z
r) and direction (δr, T,), (c) position of the center of the sub-reflector P so (xso, y
s.

ZSO), (d) Position of the center of the auxiliary reflector P to (Xto,
7t.

210). Furthermore, by determining this path, the length of the optical path from the primary radiator to the aperture surface is determined.

Next, in the second step, a partial differential equation that determines the shape of the sub-reflector 2 is determined.

FIG. 4 shows the local coordinate system at the feeding point, and FIG. 6 shows the local coordinate system at the aperture plane. Now, for crossed polarization cancellation, if the power distribution of the aperture surface and the primary radiator is rotationally symmetric, then ψ=ψ+ω (ω: constant)...(1) Here,
If the radiation pattern of the primary radiator is pt (θ) and the desired aperture power distribution is p, (ρ), then the following ordinary differential equation is derived from the law of conservation of energy.

however, py=lpr(θ) sinθdθ PA=SP, (ρ)ρdρ θe: Angle when looking into the auxiliary reflector from the feeding point.

D: Aperture diameter of the main reflecting mirror.

By solving equation (2), ρ is expressed as a function of θ only.

ρ=F(θ) (3) From equations (1) and (3), a point Pa (xm,)'m) on the aperture surface corresponding to (θ, ψ) is determined.

X11=ρcosψy )' a ”” 9 ”ψ
-(4) Now, if the main reflecting mirror 1 is a paraboloid with a focal length f as shown in FIG. ), however, a = sin” δ1 b = y, sin δa cos 6m +2
ftan crsin δ.

cos T* 2 fcos δa c = x, ” + y, “cos” δ,
+4 fsin δ8+4ftanα(XaS1n7
m '''/a CO5δ, CO3γ,) Furthermore, from Snell's law on the main reflector, the incident ray unit vector to the main reflector ν=(ν8.ν.

νt) is the reflected ray unit vector μ−(μ8.μ,.

μ, ) is always p, = sin δ, cos γ1 B, = sin δ, 5in7゜ μ1l=cos　6m Considering that it is expressed as:

vx = 1/2f-A, X, +sin δ@C
O5Tm... (7) νy = 1/2f-Az y, +sin
663417m... (8) y, =AZ +cos 6m (9) However, A! = z, +f Also, the distance t between points P and P is the center point P of the main reflecting mirror.

and the distance from the aperture surface! Then t=z-t'
... (10).

Above, the correspondence relationship equation (
1), (3), and (4), each distance r, v, u, from the feeding point to the aperture plane, and r and σ of the light unit vectors σ ξ, ξ, μ, are given, and t
and ν is determined. μ is a unit vector in the beam direction and is set from the beginning.

Therefore, the remaining unknowns are u, v, and ξ, and UV can be obtained from the following equation under the condition that the optical path length is constant.

(X++u 6 X +yIllt 6 y +Zmr
6 z −Lt )= u 2+r”+2u r
(ν× σu + shi, σ, + ν2L2 u(x*
rl/x NmtVy +2+++rl't L2 r
(X+++v+3'nf (fy +Zeaf6z
)+X m(2+V mf”+Z mfHowever, X*r
=XII Xt + 'l*t=VII Yv
.

Zsf=Za zt, Lt=L
tHere, the optical path length refers to the total distance of the light beam emitted from the feeding point P, reflected at the points PL, P, , P, and reaching the point P1 on the aperture surface. Further, the condition that the optical path length is constant is a condition that the optical path length is constant for any (θ, ψ). This condition is necessary to align the phases of the group of light rays at the aperture plane.

Using u and v in equations (11) and (12), ξ can be expressed as follows.

ξyt = (xmr-uyx-rσx)/v
...(13) ξy = (ylar-uvv-ra
y )/v °” (14) ξz = (Zsf−
Ll! /g−r(Fg)/v=
(15) All parameters can be obtained by giving r, θ, and ψ through the calculations so far.

Now, from Snell's law for the auxiliary reflector, the following partial differential equation is derived.

A, = cos θcos ψ+X/Z sin
θAz=sin θcos ψ−X/Z co
s θBI=CO3θsin ψ+X/Z s
in θBz=sin θsin ψ−X/Z
cos θX=(a, -ξx) sinrr-((
F, -ξ,)CO8T.

Y=(σX−ξX)cosδtcO5Tr+(σ,−
ξy) cos 6t sin re −(σg −
0g) sin δ.

Z−(σ to −ξ*) sin δf CO3γtNσ, −
ξy) sin δr Sin 7 y + (7r atmosphere - ξeg) cos δf By the combination of equations (1) to (17), equations (16) and (17) are the following partial differentials in the two circumferential directions in the radial direction. It turns out that it is an equation.

El r/aθ=Tθ(γ, θ, ψ) −(1B)a
γ / aψ = γψ (γ, θ, ψ) ... (19) Now,
If equations (18) and (1, 9) satisfy the fully differentiable condition, that is, aγθ/aψ=aγθ/θθ, the sub-reflector 2 and the auxiliary reflector 3 can be determined here. Shigashi style (18).

Since (19) is generally not fully differentiable, both equations cannot be made compatible at the same time. Therefore, the shape of the sub-reflector 2 is determined by ignoring equation (19) and solving the differential equation in the radial direction using only the second (18). That is, (a) ψ is fixed and treated as a constant.

(b) As an initial value, give the value of the central axis of the ray at the first stage.

(c) Solve equation (18) by numerical calculation with 0≦θ≦00.

(d) Perform the above (a) to (C) with O≦ψ and 2π.

In the process of calculation, secondary reflection! l! Obtain the shape of 2.

At this time, the shape of the auxiliary reflector is also determined at the same time.
) is completely ignored, phase errors and aberrations remain in the combination with the sub-reflector 2.

Therefore, as a third step, the shape of the auxiliary reflecting mirror 3 is determined by applying the constant optical path length condition and Snell's law to the shape of the auxiliary reflecting mirror 2 obtained previously.

That is, with respect to a certain (θ, ψ) direction, (a) the curved surface differential coefficient at point P8 on the sub-reflector is determined.

(b) Re-determine the unit vector ξ' of incidence on the sub-reflector so as to satisfy Snell's law.

(c) Find a point Pt' at which the optical path length is constant.

When this calculation is performed with 0≦θ≦θo, o≦ψ and 2π, the collection of points P1 is defined as an auxiliary reflecting mirror.

The auxiliary reflector obtained in this way is LeviCi
According to Vita's law, Snell's law should be automatically satisfied.

In addition, point pt'(χt'+ 3't'+ Zt')
is obtained from ξ′ using the following equation.

Xt =X, V ξX yt =y$-■ ξy Zz =Z, V ξ2
t=V* −Yt, Z Xt”Zs −
ZtL,,=L4-u A specific example of the above calculation is shown below. FIG. 8 shows a state in which a group of concentric circles on the aperture surface is mapped at the feeding point using this calculation method. However, the direction of the beam at this time is the same as in FIG. 9, and is as follows.

6m = 5. OCdeg) γ* -90,0 (deg) The mapping calculated by the present invention is not greatly distorted as shown in FIG. 9, and has a shape close to concentric circles.

This map shows that the aperture efficiency and cross-polarization characteristics of the multi-beam antenna have been significantly improved.

The thus obtained three-reflector system enables the following.

(a) Emit a beam in a desired direction.

(b) Completely align the phases on the aperture plane.

(C) Control the amplitude distribution in the aperture plane.

Therefore, as shown in FIG. 1, the main reflecting mirror 1 is fixed, and the auxiliary reflecting mirrors 21, 22, 23, 24 and 31, 32,
By attaching 33 and 34, a multi-beam antenna with improved aperture efficiency and cross-polarization characteristics is completed.

Note that in the present invention, the physical arrangement of the mirror system is not limited to four beams, but can be configured to emit a large number of beams.

〔Effect of the invention〕

As explained above, the present invention can improve the aperture efficiency and cross-polarized wave characteristics of a multi-beam antenna by adding an auxiliary reflecting mirror. In addition, by configuring the curved surfaces of the main reflector, sub-reflector, and auxiliary reflector to satisfy their respective conditions, the aperture efficiency and cross-polarization characteristics are improved, and the power distribution at the antenna aperture is improved. It also has the effect of making it controllable and reducing side lobes.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an embodiment of the multi-beam antenna of the present invention, and FIG. 2 is a conceptual diagram showing the optical path of one beam.
FIG. 3 is a diagram showing the relationship between the local coordinate system and the principal coordinate system in the power feeding section, FIG. 4 is a diagram showing the local coordinate system in the power feeding section,
Fig. 5 is a diagram showing the relationship between the local coordinate system and the principal coordinate system in the aperture plane, Fig. 6 is a plan view showing the local coordinate system in the aperture plane, Fig. 7 is a cross-sectional view of the main reflecting mirror, and Fig. 8 is a diagram showing the relationship between the local coordinate system and the principal coordinate system in the aperture plane. FIG. 9 is a mapping diagram of a feeding section according to the present invention, FIG. 9 is a mapping diagram of a feeding section according to a conventional antenna, and FIG. 10 is a schematic perspective view of a conventional multi-beam antenna. 1... Main reflecting mirror, 2, 21-24... Sub-reflecting mirror, 3
．． 31-34...Auxiliary reflecting mirror, 4.41-44...
Primary radiator, 5... Aperture surface, 6... Main reflecting mirror focus. Fig. 1 21-24' Sub-reflection iron 31-34', Spicy 1 cut meat 141 To 41-44:I
〉'Each 2nd Figure 3 Figure 6 Figure 7 Figure 4 Figure 5 Figure y 7't' Figure 8 Figure 9

Claims (1)

[Claims] 1. One main reflecting mirror, a plurality of sub-reflecting mirrors disposed opposite to the main reflecting mirror, and a plurality of auxiliary reflecting mirrors disposed opposite to each of these sub-reflecting mirrors. a mirror, and a plurality of primary radiators that respectively emit radio waves toward these auxiliary reflectors, and the radio waves radiated from the plurality of primary radiators are transmitted to the corresponding auxiliary reflectors; A multi-beam antenna characterized in that it is configured to be sequentially reflected by a sub-reflector and a main reflector and then radiated in a plurality of different directions. 2. The main reflecting mirror is a part of a paraboloid of revolution, and the sub-reflecting mirror has a first reflector formed of a correspondence relationship between the radiation power pattern of the primary radiator and the power distribution on the aperture surface of the main reflecting mirror. and the conditions of
A second condition in which the distances from which the light rays emitted from the phase center of the primary radiator reach a plane perpendicular to the radio wave radiation direction after being reflected by the auxiliary reflector, the sub-reflector, and the main reflector are equal to each other; , a curved surface obtained by solving the radial differential equation of the circumferential differential equation and the radial differential equation derived from the third condition that the reflection of the light beam by the auxiliary reflector follows Snell's law, When a ray of light parallel to the radiation direction of the radio wave is incident on the auxiliary reflector, the ray is reflected one after another by the main reflector, the sub-reflector, and the auxiliary reflector, and the distance to the phase center of the primary radiator is The multi-beam antenna according to claim 1, which is a curved surface determined to be equal for each light ray.