JPH0550882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an antenna device, and more particularly to an improvement in a mirror-modified offset antenna that eliminates cross-polarized components.

[Conventional technology]

FIG. 5 is a configuration diagram showing an example of a conventional mirror-modified offset antenna, which includes a conical horn 1, a hyperboloid mirror 2 as a sub-reflector, and a parabola 3 as a main reflector. The light rays along the central axis of the conical horn 1 are reflected at a point S ₀ on the hyperboloid mirror 2 and directed toward a point M ₀ on the parabola 3. And this point
The light beam reflected by M ₀ travels in a direction parallel to the mirror axis 4 of the parabola 3. Also, the focal point of hyperboloid 2 is point F ₁ ,
F ₂ , the point F ₁ coincides with the transfer center of the conical horn 1 , and the point F ₂ coincides with the focal point of the parabola 3 .

In the offset antenna constructed in this manner, a mirror system that eliminates cross-wavelength components is required from the standpoint of using orthogonal polarization. Here, even if a cross-polarized wave component is not generated in the conical horn 1, a cross-polarized wave component is generated because the main and sub-reflecting mirrors are offset mirror surfaces. In this case, if the amounts of cross-wavelength components generated by the main and sub-reflectors are equal and the polarities are opposite, the overall amount generated will be zero. The sixth one shows this situation.
In Figures a to d, the electric field distribution on the aperture surface of the horn 1 has a component in only one direction, as shown in Figure 6a, and the cross-polarized component is zero. The electric field distribution incident on the sub-reflector or the main reflector and converted is as shown in FIGS. 6b and 6c.
It has a component perpendicular to the direction of the electric field, that is, a cross-polarized component. However, since the polarities of the cross-polarized components in this case are opposite to each other, if the respective generated amounts are equal, the overall electric field distribution will be only the electric field direction component of the horn 1, as shown in FIG. 6d. In this way, the relationship between the mirror surface parameters is given so that the cross-polarized components generated on each mirror surface are equal in amount and have opposite polarities, which is called the cross-polarization cancellation condition. and,
The erasing conditions in this case are as shown in FIG. Generally, the cross-polarized components C ₂₀ and C ₃₀ generated in the sub-reflector and the main reflector are complex quantities, where the cross-polarized component C 20 is a real number and the cross-polarized component C ₂₀ is a real number.
The phase difference between C ₂₀ and C ₃₀ is defined as φ. Now, if the radiation wave from the conical horn 1 is a Gaussian beam, and the beam radii at the sub-reflector and the main reflector are ξ ₂ and ξ ₃ , then |C _i0 | (i=2, 3) is as follows. Become.

|C _i0 |=ξ _i /f _i0 tanσ _i0 /2 ...(1) Here, f ₂₀ , f ₃₀ are the focal lengths of the secondary and main reflecting mirrors when replaced with a lens system, and σ ₂₀ , σ ₃₀
is the angle between the incident ray and the reflected ray at points S ₀ and M ₀ in FIG. There are two types of cross-polarization cancellation conditions: geometric optical conditions and wave dynamic conditions. Geometric optical conditions are conditions that are applied when the wavelength of radio waves is very small compared to that of a mirror surface, and the phase difference is 0° and 180°. ,
Since |C ₂₀ |=|C ₃₀ |, the signals can be combined by simply taking the sum or difference.

The wave dynamic condition is different from the geometrical optical condition,
This is a condition that is applied when the wavelength of the radio wave is not extremely small compared to the mirror surface, and it is necessary to take into account the phase difference of the signal due to the relationship between the wavelength of the radio wave and the distance between each mirror surface when designing.

However, like the above-mentioned conventional antenna device, 2
In the single-mirror format, if the sub-reflector has a wavelength of 10 wavelengths or less, the phase difference φ will not be 180°, and the overall amount of generation cannot be reduced to zero regardless of the value of |C _i0 |, and the wave dynamic Therefore, there is no cross-polarization cancellation condition.

Although the above description assumes that both the sub and main reflecting mirrors have quadratic curved surface systems, only the geometric optics cross-polarization cancellation condition is satisfied even with a modified mirror system. Figure 8 shows the shape of the mirror surface after mirror modification with broken lines, where the light ray along the central axis of the horn 1 is at the point S ₀ on the sub-reflector and the angle σ ₂₀ is at the point S' ₀ and the angle σ ₂ , and the point M ₀ and the angle σ ₃₀ of the main reflector move to the point M′ ₀ and the angle σ ₃ .
Similarly, the focal point F ₂ moves to F′ ₂ and by substituting the changed parameters into equation (1), |C _i | can be obtained, which allows the geometric Optical conditions can be determined.

[Problem that the invention seeks to solve]

However, the conventional antenna device described above has a problem in that it cannot eliminate wave-like cross-polarized components.

Therefore, the antenna device according to the present invention has been made in order to solve the above-mentioned problem, and its purpose is to eliminate the cross-wave component wave-dynamically.

[Means for solving problems]

Therefore, the antenna device according to the present invention includes a focusing reflector (hereinafter referred to as reflector #1) and a sub-reflector (hereinafter referred to as reflector #2) that reflect radio waves radiated from the horn.
and a main reflecting mirror (hereinafter referred to as reflecting mirror #3),
The reflecting mirror #1 is made of a quadratic curved surface, and the wavelength is λ, and the beam radius of the radio wave emitted from the horn at the reflecting mirror #i (i=1, 2, 3) is ξi.
The beam radius at the beam waist position of the beam reflected by reflector #i _{is i+1} , and the distance from the beam waist position to reflector #i and reflector #(i+1) for the ray along the central axis of the horn is Z _2i and Z _2i+1 respectively, σi is the angle between the incident ray and the reflected ray at reflector #i, and the focal length is replaced by a lens system using the mirror surface shape in the plane of symmetry near the point hitting reflector #i. When defining fi as fi, the distance from the aperture of the horn to reflector #1, reflectors #1, #2, and 3, the distance between the mirror surfaces, the angle between the incident light beam and the reflected light beam, and the shape of the mirror surface within the plane of symmetry in the vicinity of the point where the light beam hits are determined.

C ₁ cosφ _i +C ₂ −C ₃ cosφ ₂ =0 C ₁ sinφ ₁ +C ₃ sinφ ₂ =0 Here, C _i =ξ _i / f _i tanσ _i /2 φ _i = tan ^-1 [Z _2i+1 / k(ξ _i+1 ) ² 〕−tan ^-1 〔Z _2i /
k(ξ _i+1 ) ² ] (i=1, 2, 3) k=2π/λ [Operation] The antenna device according to the present invention takes into account the beam waist position, etc., and adjusts the arrangement of each mirror surface, radius of curvature, etc. By determining the wave dynamic conditions), it is possible to eliminate wave-like cross-wavelength components in an antenna device in which the size of the mirror surface is sufficiently small compared to the wavelength (for example, 10 wavelengths or less).

〔Example〕

FIG. 1 is a schematic configuration diagram showing an embodiment of an antenna device according to the present invention, and the same parts as in FIG. 5 are shown using the same symbols. In the figure, 5 is a modification sub-reflector, 6 is a modification main reflector, and 7 is a focusing reflector. Here, the ray of light along the axis of horn 1 is
After being reflected at point Q ₀ on the focusing reflector 7, which is a hyperbolic offset mirror surface, it heads into space via points S ₀ ' and M ₀ ', as in the case of FIG. Here, the point
Let the angle between the incident ray and the reflected ray at Q ₀ be σ ₁ , and the focal lengths when the focusing reflector 7, modifying sub-reflector 5, and modifying main reflector 6 are replaced with lens systems are f ₁ and f ₂ , respectively. , f ₃ , and the mirror surface numbers are # ₁ , # ₂ ,
# ₃ . Note that the radiation wave from the horn 1 is a Gaussian beam, and the beam radius at _#i (i=1, 2, 3) is _ξi .

At this time, the peak value Cm of the cross-wavelength level generated in the three-mirror system is as follows.

Cm=10logCreal+Cing/e, (dB) Creal=C ₁ cosφ ₁ +C ₂ −C ₃ cosφ ₂ Cing=C ₁ sinφ ₁ +C ₃ sinφ ₂ ...(2) Here, e=2.718, Ci is mirror surface _#i This is the generated cross-wave component, and φ _i is the phase difference between the components at mirror surfaces # ₁ and # ₃ based on the cross-wave component at mirror surface # ₂ , and is given by the following equation.

C _i =ξ _i /f _i tanσ _i /2 φ _i = tan ^-1 [Z _2i+1 /k(ξ _i+1 ) ² ]−tan ^-1 [Z _2i /
k(ξ _i+1 ) ² ] K=2π/λ ...(3) Here, λ is the wavelength, _i+1 is the beam radius at the waist position of the beam reflected by mirror surface _#i , Z _2i ,
Z _2i+1 is mirror surface _#i , #(i
+1). Also, the aperture diameter of horn 1 is A ₀ , the length is N ₀ , the distance from the horn aperture surface to mirror surface # ₁ is W ₀ , and the distance between mirror surface # _i and mirror surface # _(i+1) is
W _i , the beam radius at the aperture of the horn is ξ ₀ ,
Let R ₀ be the radius of curvature of the wavefront, R _2i-1 be the radius of curvature of the incident wavefront on mirror surface _#i , and R _2i be the radius of curvature of the reflected wavefront. Here, ξ ₀ , R ₀ and A ₀ , N ₆ have the following relationship.

ξ ₀ =aA ₀ , R ₀ =N ₀ (4) Now, if horn 1 is a corrugated horn with EH ₁₁ mode excitation, α will be 0.322.

In this way, the specifications of horn 1 are given, and formula (3)
The design parameters for each mirror surface are determined as follows from the conditions for making Ci zero.

₁ = ξ ₀ /√1+v ₀ ² , v ₀ = kξ ₀ ² /R ₀ Z ₀ = R ₀ /1+1/v ₀ ² , Z ₁ =Z ₀ +W ₀ ξ ₁ = ₁ √1+ ₁ ² , v ₁ = Z ₁ /kξ ₁ ² ...(5) , R ₁ =Z ₁ (1+1/v ₁ ² ) 1/f ₁ =1/R ₁ -1/R ₂ ...(6) ₂ =ξ ₁ /√1+v ₂ ² , v ₂ = kξ ₁ ² /R ₂ Z ₂ = R ₂ /1+1/v ₂ ² , Z ₃ =Z ₂ +W ₁ ξ ₂ = _2√1 + ₃ ² , v ₃ =Z ₃ /kξ ₂ ² ... …(7) R ₃ = Z ₃ (1+1/v ₃ ² ) R ₄ = [R ₂₂ /ξ ₂ ² −W ₁ /ξ ₁ ² R ₁₁ /f ₁
R ₂ / (R ₂ + W ₁ )] W ₂ / W ₂ / ξ ₂ ² (R ₁₁ / f ₁ + R ₂₂ / R ₃ ) +
W ₁ /ξ ₁ ² R ₁₁ /f ₁ R ₂ / (R ₂ + W ₁ ), R _ii =ξ _i tanσ _i /
2 1/f ₂ = 1/R ₃ -1/R ₄ ...(8) ₃ =ξ ₂ /√1+v ₄ ² ₁ v ₄ = kξ ₂ ² /R ₄ Z ₄ = R ₄ /1+1/v ₄ ² , Z ₅ = Z ₄ + W ₂ ξ ₃ = ₃ √1 + ₅ ² , v ₅ = Z ₅ /kξ ₃ ² ...(9) R ₅ = Z ₅ (1 + 1/v ₅ ² ) 1/f ₃ = 1/ R ₅ tanσ ₃ /2=R ₁₁ /f ₁ +R ₂₂ /f ₂ /ξ ₃ /f ₃ ...(10) Then, when the parameters of the mirror system are determined as shown in equations (5) to (10) The cross-polarized component at is the second
It is erased as shown in the figure.

In addition, the focal length f _i when replacing it with a lens system
Of these, f ₁ is easily determined because mirror surface # ₁ is a quadratic curved surface, but f ₂ and f ₃ are not clearly determined because mirror surfaces # ₂ and # ₃ are modified mirror surfaces. However, it has been reported that a modified mirror surface can be represented as a group of quadratic surfaces with different constants, and it is also known that the amount of cross-polarized components generated is related to the shape of the mirror surface at the center of the mirror surface. Therefore, the constants of the quadratic surface system in the plane of symmetry at points S ₀ ′ and M ₀ ′ in FIG. 1 can be used. The constants of this quadratic surface system can be determined as follows using FIG.
Here, 5, 6, and 7 are the same as in FIG. 1, and 8 is an image horn formed by the focusing reflector 7 of the horn 1. If the aperture diameter of this image horn 8 is A ₀ ' and the length is N ₀ ', these can be determined from the following equation.

1/f ₁ = 1/W ₀ −1/W ₀ ′=1/W ₀ +N ₀ −1/W′ ₀ +
N' ₀ A' ₀ = A ₀ | W ₀ '/W ₀ | ...(11) Here, since f ₁ , W ₀ , A ₀ , and N ₀ are known, the specifications of the image horn 8 can be found. . FIG. 4 shows a mirror system within the plane of symmetry using this image horn 8. Here, the primary radiator is the image horn 8 shown in FIG. 3, and in the quadratic curved surface system before the mirror surface is modified, 9 is a rotationally symmetrical sub-reflector and 10 is a rotationally symmetrical main reflector. Further, in the mirror system for mirror surface modification control, numeral 11 is a rotationally symmetrical modification sub-reflector, and 12 is a rotationally symmetrical modification main reflecting mirror. It is known that in such a rotationally symmetric system, if the required aperture distribution is determined by giving a quadratic curve system as an initial value, the mirror surface modification system can be determined. Here, the opening diameter Dm is the third
Both Fig. 4 and Fig. 4 are the same.

In the above embodiments, the sub-reflecting mirror and the main reflecting mirror are modified mirror surfaces, but they may also be quadratic curved surfaces. In addition, in the above embodiment, one focusing reflector 7 was provided between the sub-reflector 5 and the horn 1, but N
A similar effect can be obtained when a number of focusing reflectors are provided, and in this case, the horn image formed by (N-1) focusing reflectors may be replaced with the horn of the above embodiment. .

〔Effect of the invention〕

As explained above, in the antenna device according to the present invention, by determining the arrangement of each mirror surface, the radius of curvature, etc. (wave dynamic conditions) in consideration of the beam waist position, etc., the size of the mirror surface is sufficiently large compared to the wavelength. In a small antenna device (for example, 10 wavelengths or less), it has an excellent effect of being able to wave-dynamically cancel cross-polarized components.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the antenna device according to the present invention, FIGS. 2, 3, and 4 are configuration diagrams for explaining the operation of the antenna device shown in FIG. The figure is a schematic configuration diagram showing an example of a conventional antenna device, and FIGS. 6, 7, and 8 are configuration diagrams for explaining the operation of the conventional antenna device. 1...Horn, 2...Hyperboloid mirror, 3...Parabola, 4...Mirror axis, 5...Modified sub-reflector, 6...Modified main reflector, 7...Focusing reflector, 8...Image Horn, 9...Rotationally symmetrical (secondary) sub-reflector, 1
0...Rotationally symmetrical (secondary) main reflecting mirror, 11...Rotationally symmetrical modified sub-reflecting mirror, 12... Rotationally symmetrical modified main reflecting mirror. Note that the same or equivalent parts in the figures are indicated using the same symbols.

Claims (1)

[Claims] 1. A horn with a central axis, a focusing reflector (hereinafter referred to as reflector #1) that reflects radio waves emitted from the horn, a sub-reflector (hereinafter referred to as reflector #2), and a main reflector. (hereinafter referred to as reflecting mirror #3), and wherein the reflecting mirror #2 and the reflecting mirror #3 are curved surfaces that can obtain a required aperture distribution on the aperture surface of the reflecting mirror #3. The reflecting mirror #1 is composed of a quadratic curved surface, and the wavelength is λ, and the reflecting mirror #i (i=1, 2,
3) is the beam radius at ξi, the beam radius at the beam waist position of the beam reflected by reflector #i _{is i+1} , and the beam radius at the beam waist position of the beam reflected by reflector #i is i+1. The distance to #(i+1) is Z _2i and
Z _2i+1 , σi is the angle formed by the incident ray and reflected ray at reflector #i, and fi is the focal length replaced by a lens system using the mirror surface shape in the plane of symmetry near the point hitting reflector #i. When doing so, the distance from the aperture of the horn to reflector #1, the distance between the mirror surfaces of reflectors #1, #2, and #3 for the ray along the central axis of the horn, and the distance between the mirror surfaces of reflectors #1, #2, and #3 are determined so that the following equation is approximately satisfied. distance,
An antenna device characterized in that the angle formed by an incident light beam and a reflected light beam, and the shape of a mirror surface in a plane of symmetry in the vicinity of a point where the light beam hits are determined. C ₁ cosφ _i +C ₂ −C ₃ cosφ ₂ =0 C ₁ sinφ ₁ +C ₃ sinφ ₂ =0 Here, C _i =ξ _i / f _i tanσ _i /2 φ _i = tan ^-1 [Z _2i+1 / k(ξ _i+1 ) ² 〕−tan ^-1 〔Z _2i /
k(ξ _i+1 ) ² ] (i=1, 2, 3) k=2π/λ 2 Claim 1, characterized in that the focusing reflector is replaced with a plurality of quadratic curved surfaces. The antenna device described.