JPS605619Y2 - Offset type aperture antenna - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an offset type aperture antenna using a non-quadratic curved surface as a reflecting mirror.

Conventionally, there is an example of an offset type aperture antenna having an axially symmetric aperture distribution as shown in FIG.

This antenna consists of A1-A in the figure, a parabolic mirror 1 with two rotation axes and F2 as the focal point, a hyperboloid mirror 2 with A2-A2a as the rotation axis and focal points at Fl and F2, and A with Fl as the apex.
Primary radiator 3 of conical horn with rotation axis at G A3&
It consists of

In this case, let the eccentricity of the hyperboloid reflector 2 be e, and let the inclinations of each of the three axes be α and β as shown in the figure, and if the relationship between these quantities is maintained, the aperture distribution will be It is axially symmetrical.

This axial symmetry of the aperture distribution not only relieves the deterioration of the cross-polarized wave characteristics characteristic of offset antennas, but is also known to improve the gain and gradually reduce the side lobe level. .

However, as can be seen from the above example, when an offset double reflector is configured with a quadratic reflector, if the aperture distribution is to be made axially symmetrical, the reflector axis and primary radiator are They must be installed at an angle to each other so as to satisfy the equation, which not only makes the setting between the elements complicated and difficult, but also has the drawback of increasing the space occupied by the antenna.

The present invention maintains that the aperture distribution is axially symmetrical,
The object of the present invention is to provide an offset type aperture antenna that eliminates the above-mentioned drawbacks.

The present invention will be explained in detail below using the drawings.

FIG. 2 is a schematic configuration diagram of an antenna for explaining the principle of the present invention, and a point P1 on the sub-reflecting mirror surface 2 is represented by spherical coordinates (rt θ, φ) with 01 as the vertex.

Moreover, point P2 on the main reflecting mirror 1 is in the spherical coordinates (y, ρ, φ
).

Here, it is assumed that the X axis and the Z axis are parallel to each other in both coordinate systems.

When the coordinate system is determined in this way and the axis A1-A1a of the primary radiator 3 of the conical horn is aligned with the Z axis and parallel to the rays reflected and emitted by the main reflecting mirror, 4. Find the shape of the reflecting mirror surface as follows.

First, assuming that the reflection law ends at point P2 on the main reflecting mirror surface 1, the following equation is obtained.

3z= -a Sin -r SinθCO3(2)
;f) p S+r C
O3θ -2a7. r Sin 03in (φ-can 3
00 groan (3)E)4t s+r cos
Similarly to θ-2, the following equation is obtained at point P1 of the sub-reflecting mirror surface 2.

Next, the conditions for the radio waves emitted from the origin 0□ to have the same phase on the antenna aperture surface, that is, for the radio wave path length from 01 to all points on the aperture surface to be constant, are as follows.

s+r-2=1 Φ(θ)/k (61 Here, it is assumed that the primary radiator 3 has an axially symmetrical radiation characteristic, and the radio waves emitted from the -order radiator 3 generally have a true wave with the phase center at 01. Considering that it is slightly different from a spherical wave, this phase shift was defined as Φ(θ).

Also, K is K = ro Zo + J (zo + ro
:)2+a2 (r,, zo is the initial value), S is the length from Pl to P2, and k is the propagation constant.

To simplify the explanation below, in equation (6), Φ(θ)
The case where = 0 will be explained.

In order for the -order radiator 3 to have an axially symmetrical radiation characteristic and to be axially symmetrical on the antenna aperture plane, 1(θ.

φ) and (ρ.

φ), that is, −mi− is a function of only p and θ, and the relationship δθ and φ=ψ (8-I) or φ+f (8-II) must be satisfied.

By rewriting equations (2) to (5) using equations (7) and (8), the following first-order simultaneous partial differential equations with θ and ψ as independent variables are obtained.

In each formula, decoding is performed by formula (8-I) on the top and formula (8-II) on the bottom.
) formulas are used.

Here, the solution that satisfies the differential equation when the upper sign is taken is called the mirror system I, and the solution when the lower sign is taken is called the mirror system ■.

Now, in order to obtain a realizable curved surface, if we apply the integrability condition to this simultaneous -order partial differential equation, we find that equation (7) must hold.

I was able to integrate This is easy is obtained.

XL is an arbitrary constant. (Using equation 1, numerically solve partial differential equation systems I and ■ (i.e., mirror systems I and ■) to obtain a curved surface, that is, a -order radiator and subreflector parallel to the main beam of the antenna. It is possible to obtain an offset type aperture antenna in which the aperture distribution is axially symmetrical even when the antenna is disposed in the same direction.

1 and 2 in FIG. 3 show part of the curved surfaces of the main and sub-reflectors obtained in this way, including the position of the primary radiator 3, and the initial value r (0, ±7) = 309 2 (09
(shiryo) = 5, the constants are xL = 460 and a = 50
The curve obtained by solving the mirror system ■ is shown as .

1 and 2 in FIG. 4 are the same mirror system I with initial values r(0,
□□□=309 2 (This is a curve solved with ot9=5.

Next, Figure 5 shows the curve obtained by solving the mirror system ■, with the initial value r (09
``')=30.z (o 壬子)2=5, the curve obtained with constant XL=460 and a=50 is shown.

The above description is based on the case where the phase characteristic of the primary radiator 3 is ideal, that is, when Φ(θ)=0, but in reality, Φ(θ) is NO in most cases.

However, even in that case, it is obvious that the reflective mirror surface can be easily determined based on equation (6).

Also, in the above it is assumed that a spherical wave is emitted from the apex of the conical horn, but in reality, the radio wave is emitted from the phase center, so the actual θ is the point P between the phase center of the primary radiator 3 of the conical horn and the arbitrary point P on the sub-reflector 2. This is the angle between the line 4 connecting the radiator and the axis of the primary radiator 3.

This antenna has excellent electrical performance and can be made compact, making it suitable for use as a ground-to-ground relay antenna or as an antenna mounted on a satellite.

As explained above, the offset type aperture antenna according to the present invention uses non-quadratic curved surfaces for the main reflector and the sub-reflector to obtain an axially symmetric aperture density distribution. Unlike conventional antennas of this type that use curved surfaces, there is no need to tilt the reflector axis and primary radiator axis, and there is no need to rotate the reflector, so it is easy to set up each element. Similarly, the antenna itself can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an offset type antenna with a rotationally symmetrical aperture distribution in which the conventional reflecting mirror surface is constructed of a quadratic curved surface, and FIG. 2 is a diagram for explaining the antenna of the present invention.
Figure 49 Figure 5 is a diagram showing an embodiment of the present invention. 1... Main reflecting mirror, 2... Sub reflecting mirror, 3
・・・・・・−Next radiator.

Claims (1)

[Scope of utility model registration request] In an offset-type aperture antenna equipped with a main reflector, a sub-reflector, and a conical horn primary radiator, a beam extending in the direction of a line connecting the phase center of the conical horn and an arbitrary point on the sub-reflector When a radio wave reaches a point at a distance ρ from the center on the antenna aperture surface reflected by both of the reflecting mirrors, the angle θ between the direction and the axis of the conical horn and the distance ρ
The mirror surfaces of both reflecting mirrors are configured so as to substantially satisfy the relationship between 2
An offset type aperture antenna characterized in that both of the reflecting mirrors and the -order radiator are arranged using a second-order curved surface.