JP3149432B2 - Multi-beam antenna - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam antenna that enables simultaneous communication with a plurality of satellites in a geosynchronous orbit with one antenna.

[Conventional technology]

In a conventional multi-beam antenna, for example, as shown in FIG. 10, one main reflecting mirror 1 is used in common for a plurality of (here, four) beams, and one sub-reflecting mirror 21 to 24 is provided for each beam. There are some that correspond. The main reflecting mirror 1 is a parabolic surface or a secondary curved surface such as a torus, and the shapes of the sub-reflecting mirrors 21 to 24 are adjusted so that the optical path length from the feed 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 that the light beams emitted from the feeding points P _f1 , P _f2 , P _f3 , P _f4 are respectively reflected by the sub-reflecting mirrors 21, 22, 23, 24 and the main reflecting mirror 1 and reach the respective aperture surfaces. Is the total distance to

[Problems to be solved by the invention]

However, in the above-described conventional multi-beam antenna, when calculating the shape of the sub-reflector, the correspondence between the radiation pattern of the primary radiator and the power distribution on the aperture is not taken into account, so that the power on the aperture is not considered. You cannot control the distribution.

As a result, a mapping distortion occurs between the two as shown in FIG. The mapping referred to here is an image formed on a virtual plane in front of the power supply unit when a group of concentric circles on the aperture surface enters the main reflecting mirror 1 as parallel rays. If this mapping is distorted, the power on the antenna aperture will be biased, and the aperture efficiency will decrease.Also, even if the polarization direction of the primary radiator is constant, the polarization direction at the aperture surface will not be constant, so Wave 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 problem]

The multi-beam antenna according to the present invention includes a plurality of auxiliary reflectors provided between a plurality of sub-reflectors opposed to one main reflector and a plurality of primary radiators for emitting radio waves. Are radiated in a plurality of different directions after being sequentially reflected by the corresponding auxiliary reflecting mirror, sub-reflecting mirror, and main reflecting mirror, respectively.

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

The sub-reflector has a first condition consisting of a correspondence relationship between a radiation power pattern of the primary radiator and a power distribution on an opening surface of the main reflector, and a light beam emitted from the phase center of the primary radiator. Are reflected by the auxiliary reflector, the sub-reflector and the main reflector so that the distances to the plane perpendicular to the radio wave radiation direction are equal to each other. Of the circumferential differential equation and the radial differential equation derived from the third condition of obeying the law, the surface is formed by a curved surface obtained by solving the radial differential equation.

Further, when the auxiliary reflecting mirror makes light rays parallel to the radiation direction of the radio wave incident, the light rays are sequentially reflected by the main reflecting mirror, the sub-reflecting mirror and the auxiliary reflecting mirror, and reach the phase center of the primary radiator. It is constituted by a curved surface whose distance is determined to be equal for each ray.

[Action]

According to the present invention, by adding the 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 reflecting mirror, the sub-reflecting mirror, and the auxiliary reflecting mirror so as to satisfy the respective conditions, the aperture efficiency and cross polarization characteristics are improved, and the power distribution at the antenna aperture surface is reduced. Controllable.

〔Example〕

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

FIG. 1 is a schematic perspective view of one embodiment of the present invention,
Here, an example in which the present invention is applied to a four-beam multi-beam antenna is shown. In the figure, reference numeral 1 denotes a main reflecting mirror, which is constituted by an offset type paraboloid, and has beams 1, 2, 3, 4
It is shared by. The sub-reflecting mirrors 21, 22, 23, 24 corresponding to the beams 1, 2, 3, 4 and the primary radiators 41, 42, 43, 44 as feed points P _f2 , P _f3 , P _f4 of each beam, Auxiliary reflector 3 between
1,32,33,34 are provided. The sub-reflectors 21 to 24
And the auxiliary reflecting mirrors 31 to 34 are configured as mirror surfaces adjusted in accordance with the directions of the beams 1 to 4, respectively.

In this multi-beam antenna, for example,
The light rays emitted from P _f1 are the auxiliary reflecting mirror 31, the sub-reflecting mirror 21,
The light is sequentially reflected by the main reflecting mirror 1 and becomes a parallel ray as a beam 1. Similarly, the light beams emitted from the feeding points P _f2 , P _f3 , P _f4 are respectively the auxiliary reflecting mirrors 32, 33, 34, and the sub-reflecting mirrors 21, 2,
The beams are reflected by the main reflection mirrors 2 and 23 and the main reflection mirror 1 to form a parallel configuration as beams 2, 3, and 4.

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

First, in the first stage, the path of the central axis of the ray group is determined.
That is, the direction of the beam, the position and direction of the primary radiator as the feeding point, and the position of the center of the sub-reflector and the auxiliary reflector are determined.

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

In the third stage, the shape of the auxiliary reflecting mirror is obtained from the shape of the sub-reflecting mirror obtained in the second stage and the condition for keeping the optical path length constant.

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

FIG. 2 is a diagram showing a calculation method. Primary radiator 4 of the feeding point P rays emitted from the _f points P _t on the auxiliary reflecting mirror 3, point P _s on the sub-reflector 2 and is reflected at a point P _m on the main reflector 1,
It has come to a point P _a on the opening surface 5. The opening surface 5 is that of a plane perpendicular to the beam direction, wherein a direction viewed point P _a from the point P _m is is the beam direction.

Points P _t0 , P _s0 , P _m0 , and P _a0 are the centers of the auxiliary reflecting mirror 3, the sub-reflecting mirror 2, the main reflecting mirror 1, and the aperture 5, respectively, and are the centers of the group of rays emitted from the feeding point P _f. It shows the path taken by the axis.

In the following calculations, the point P _f point from P _t, the point P _t point from P _s,
The point P _s point from P _m, respectively unit vectors of light rays from the point P _m and the point _{P a σ, ξ, ν,} μ, also between the points P _f P _t, between the points P _t P _s,
The distances between the points P _s P _m and the points P _m P _a are defined as r, u, v, t, respectively.

FIG. 3 shows how the actual angles of the directions (δ _f , γ _f ) of the primary radiator 4 are set. FIG. 3 shows the relationship between the local coordinate system x′y′z ′ and the main coordinate system xyz in the power supply unit,
The positive direction of the z 'axis coincides with the direction of the primary radiator. Light ray groups are emitted to from the primary radiator, as shown in FIG. 4, the conical opening angle theta _c. The direction of each ray in the ray group is represented by (θ, ψ) as shown in FIG.

Similarly, FIG. 5 shows a local coordinate system x "y" on the aperture plane.
This represents the relationship between z ″ and the main coordinate system xyz. The beam direction (δ _a , γ _a ) coincides with the positive z ″ axis direction in the local coordinate system.

FIG. 6 shows a local coordinate system on the aperture surface 5, in which the cross section of the light ray group is drawn as a circle. Opening angle θ _{c at the} feeder
The light ray group within the cone of FIG. 3 reaches the inside of the circle having the diameter D on the aperture surface 5 after being reflected three times. The direction of each light beam on the aperture surface 5 is perpendicular to the aperture surface 5 and coincides with the positive direction of the z ″ axis.
It is represented by (P, Ψ) as shown in FIG.

The first step in the present calculation method is to determine the central axis of the light beam. This path first determines (a) the desired beam direction (δ _a , γ _a ).

On the other hand, (b) the position P _f (x _f , y _f , z _f ) and direction (δ _f , γ) of the primary radiator so that the mirror system is physically feasible and has an appropriate shape.
_f), (position of the center of c) sub-reflector _{P s0 (x s0, y s0} , z s0), and, (d) position of the center of the auxiliary reflector _{P t0 (x t0, y t0} , z t0) By choosing each one, it is uniquely determined. Also, by determining this path, the optical path length L from the primary radiator to the aperture surface is determined.

Next, as a second stage, a partial differential equation that determines the shape of the sub-reflector 2 is obtained.

FIG. 4 shows a local coordinate system at the feeding point, and FIG. 6 shows a local coordinate system at the opening surface. Now, assuming that the aperture plane and the power distribution of the primary radiator are rotationally symmetric for cross polarization cancellation, Ψ = ψ + ω (ω: constant) (1) where the radiation pattern of the primary radiator is p _f Assuming that (θ) and the desired aperture power distribution are p _a (ρ), the following ordinary differential equation is derived from the law of conservation of energy.

Where, P _F = ∫P _f (θ) sin θd θ P _A = ∫P _a (ρ) ρdρ θ _C : Angle at which the auxiliary reflecting mirror is seen from the feed point, D: Opening diameter of the main reflecting mirror.

By solving equation (2), ρ is represented by a function of only θ.

ρ = F (θ) ... ( 3) Equation (1), (3) from (theta, [psi) point on the aperture plane corresponding to _{P a (x a, y a} ) is determined.

x _a = ρcosΨ, if y _a = ρsinΨ ... (4) Now, paraboloid of focal length f as shown the main reflector 1 in FIG. 7, a point on the main reflector corresponding to the point P _a P
_m (x _m , y _m , z _m ) _{^{However, a = sin 2 δ a b}} = y a sinδ a cosδ a + 2f tanαsinδ a cosγ a -2f cosδ a c = x a 2 + y a 2 cos 2 δ a + 4f sinδ a + 4f tanα (x a sinγ a + y a cosδ _a cosγ _a ) Further, from Snell's law on the main reflecting mirror, the incident light unit vector ν = (ν _x , ν _y , ν _z ) on the main reflecting mirror is the reflected light unit vector μ = (μ _x , μ _y) , mu _z) always considering that represented by _{μ x = sinδ a cosγ a μ} y = sinδ a sinγ a μ z = cosδ a, as follows.

_{ν x = -1 / 2f · A} z x m + sinδ a cosγ a ... (7) ν y = -1 / 2f · A z y m + sinδ a sinγ a ... (8) ν z = A 2 + cosδ a (9) However The distance t between the point P _m P _a is become if the distance between the center point P _m0 and the opening surface of the main reflecting mirror and l t = l-t '... (10).

Above, the orientation of the light beam from the feeding point (theta, [psi) and a point on the aperture plane _{P a (x a, y a} ) corresponding relation between (1), (3),
According to (4), each distance r, from the feeding point to the opening surface,
v, u, t and the ray unit vector σ ξ, ν, μ, r
And σ were given, and t and ν were determined. μ is a unit vector in the beam direction, which is set from the beginning.

Therefore, the remaining unknowns are u, v and ξ, but u, v is obtained by the following equation from the condition that the optical path length is constant.

v ² = u ² + r ² + 2ur (ν _x σ _x + ν _y σ _y + ν _z σ _z ) −2
_{u (x mf ν x + y} mf ν y + z mf ν z) -2r (x mf σ x + y mf σ
_{y + z mf σ z) +} x mf 2 + y mf 2 + z mf 2 ... (12) _{However, x mf = x m -x f} , y mf = y m -y f, z mf = z m -z f, L t = L
−t Here, the optical path length is a point at which the light beam emitted from the feeding point P _f is a point.
It indicates the total distance of a path that is reflected by P _t , P _s , and P _m and reaches _a point Pa on the aperture surface. The constant optical path length condition is a condition that the optical path length is constant for any (θ, ψ). This condition is necessary in order to align the phases of the optical path groups on the aperture surface.

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

_{ξ x = (x mf -uν x} -rσ x) / v ... (13) ξ y = (y mf -uν y -rσ y) / v ... (14) ξ z = (z mf -uν z -rσ z ) / V ... (15) If r, θ, and に よ り are given by the calculations up to this point, all parameters can be obtained.

The following partial differential equation is derived from Snell's law in the auxiliary reflecting mirror.

_{However, A 1 = cosθcosψ + X /} Zsinθ A 2 = sinθcosψ-X / Zcosθ B 1 = cosθsinψ + X / Zsinθ B 2 = sinθsinψ-X / Zcosθ X = (σ x -ξ x) sinγ f - (σ y -ξ y) cosγ _{f Y = (σ x -ξ x} ) cosδ f cosγ f + (σ y -ξ y) cosδ f sinγ f - (σ z -ξ z) sinδ f Z = (σ x -ξ x) sinδ f cosγ f + (σ _y -ξ _y) by a combination of _{sinδ f sinγ f + (σ z} -ξ z) cosδ f above formula (1) to (17), formula (1
6) and (17) are the following partial differential equations in the radial and circumferential directions.

∂γ / ∂θ = γθ (γ, θ, ψ) ... (18) ∂γ / ∂ψ = γψ (γ, θ, ψ) ... (19) Now, equations (18) and (19) are fully differentiable. If the condition, ie, ∂γθ / ∂ψ = ∂ψγθ / ∂θ, is satisfied, the sub-reflecting mirror 2 and the auxiliary reflecting mirror 3 can be determined here. However, since equations (18) and (19) are generally not totally differentiable, they cannot be compatible at the same time. Therefore, the shape of the sub-reflector 2 is determined by solving the differential equation in the radial direction only with the expression (18), ignoring the expression (19). That is, (a) ψ is fixed and treated as a constant.

(B) As the initial value, the value of the light axis at the first stage is given.

(C) a formula (18) with 0 ≦ θ ≦ θ _c solved numerically.

(D) Perform the above (a) to (c) with 0 ≦ ψ <2π.

, The shape of the sub-reflection mirror 2 is obtained. At this time, the shape of the auxiliary reflecting mirror is determined at the same time, but since the expression (19) is completely ignored, the phase error and aberration remain in combination with the sub-reflecting mirror 2.

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

That is, for a certain (θ, ψ) direction, (a) a curved surface derivative at a point P _s on the sub-reflector is obtained.

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

(C) Find a point P _t 'at which the optical path length is constant.

Is calculated as 0 ≦ θ ≦ θ _c , 0 ≦ ψ <2π, an aggregate of the points _Pt is set as an auxiliary reflecting mirror. According to Levi-Civita's law, the auxiliary reflector determined in this way is:
Snell's law should be satisfied automatically.

The point P _t ′ (x _t ′, y _t ′, z _t ′) is obtained from か ら ′ by the following equation.

_{x t '= x s -v'ξx'} y t '= y s -v'ξy' z t '= z s -v'ξz' x _sf = x _s −x _f , y _sf = y _s −y _f , z _sf = z _s −z _f L _tu = L−t−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 by the present calculation method. However, the direction of the beam at this time is the same as in FIG. 9, and is as follows.

δ _a = 5.0 [deg] γ _a = −90.0 [deg] The mapping by the calculation of the present invention has a shape close to a concentric circle without significant distortion as shown in FIG. This mapping shows that the aperture efficiency and cross polarization characteristics of the multi-beam antenna have been greatly improved.

The three-mirror system thus obtained allows the following:

(A) A beam is emitted in a desired direction.

(B) Completely align the phases in the aperture plane.

(C) Control the amplitude distribution on the aperture surface.

Therefore, as shown in FIG. 1, the main reflecting mirror 1 is fixed,
For each of the beams 1, 2, 3, 4
If you attach 1,22,23,24 and auxiliary reflectors 31,32,33,34,
A multi-beam antenna with improved aperture efficiency and cross polarization characteristics is completed.

It should be noted that, in the present invention, the physical arrangement of the mirror surface
It is possible to configure to emit many beams without being limited to one beam.

〔The invention's effect〕

As described above, the present invention can improve the aperture efficiency and cross polarization characteristics of the multi-beam antenna by adding the auxiliary reflecting mirror. In addition, by configuring the curved surfaces of the main reflecting mirror, the sub-reflecting mirror, and the auxiliary reflecting mirror so as to satisfy the respective conditions, the aperture efficiency and cross polarization characteristics are improved, and the power distribution at the antenna aperture surface is reduced. There is also an effect that control is possible and side lobes can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of one embodiment of a multi-beam antenna of the present invention, FIG. 2 is a conceptual diagram showing an optical path of one beam,
FIG. 3 is a diagram showing a relationship between a local coordinate system and a main coordinate system in the power supply unit, FIG. 4 is a diagram showing a local coordinate system in the power supply unit,
FIG. 5 is a diagram showing the relationship between the local coordinate system and the main coordinate system on the aperture surface, FIG. 6 is a plan view showing the local coordinate system on the aperture surface, FIG. 7 is a sectional view of the main reflector, and FIG. FIG. 9 is a schematic diagram of a power supply unit using a conventional antenna, and FIG. 10 is a schematic perspective view of a conventional multi-beam antenna. 1… Main reflector, 2,21-24… Sub reflector, 3,31-34…
Auxiliary reflector, 4,41-44 ... Primary radiator, 5 ... Opening surface,
6: Focus of the main reflector.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01Q 19/19 H01Q 25/00

Claims (2)

(57) [Claims] 1. A main reflecting mirror, a plurality of sub-reflecting mirrors disposed opposite to the main reflecting mirror, and a plurality of auxiliary reflecting mirrors provided to oppose the sub-reflecting mirrors, respectively. A plurality of primary radiators for radiating radio waves toward these auxiliary reflecting mirrors, respectively; radio waves radiated from the plurality of primary radiators respectively correspond to the corresponding auxiliary reflecting mirrors;
A multi-beam antenna, wherein the multi-beam antenna 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.
The sub-reflector has a first condition consisting of a correspondence relationship between a radiation power pattern of the primary radiator and a power distribution on an opening surface of the main reflector, and a light beam emitted from the phase center of the primary radiator is The second condition that the distances from the auxiliary reflector, the sub-reflector, and the main reflector to the plane perpendicular to the radio wave radiation direction after being reflected is equal to each other, and the reflection of the light beam by the auxiliary reflector is Snell's law. Out of the circumferential differential equation and the radial differential equation derived from the third condition of obeying the following condition: a curved surface obtained by solving a radial differential equation; Are incident on the main reflector, the sub-reflector and the auxiliary reflector, and the curved surface is determined so that the distance to the phase center of the primary radiator is equal for each light. Patent contract Multibeam antenna ranging preceding claim.