JP3314904B2 - Multi-beam antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam antenna having a reflecting mirror, and more particularly to a multi-beam antenna having a contoured reflecting mirror capable of improving directional characteristics and side lobe characteristics.

[0002]

2. Description of the Related Art FIG. 1 is a diagram for explaining a multi-beam antenna. In the figure, numeral 1 denotes a reflecting mirror, 2a,
Reference numerals 2b and 2c denote primary radiators, and reference numerals 3a, 3b and 3c denote trajectories of beams emitted from the primary radiators 2a to 2c, respectively. As described above, the multi-beam antenna emits a plurality of beams from one antenna. Generally, each beam has feed points A to C corresponding to each beam.

One of the factors that deteriorates the directional characteristics of an antenna is
One is blocking (a part of the antenna structure blocks radio waves radiated from the reflector). Since the multi-beam antenna has a plurality of primary radiators, the presence of blocking by the primary radiators and their supporting columns not only makes the design difficult, but also limits the achievable radiation pattern, and the loss cannot be ignored.

Accordingly, an offset type in which the primary radiator system (the primary radiator and its peripheral circuits) does not exist in the radio wave path in front of the reflector is generally used. The contour of the reflector is determined so that the irradiation beam from the primary radiator is effectively received with a limited aperture area, and the power that spills over (the power that leaks without hitting the reflector) is reduced. ,
It has a shape close to a circle or an ellipse.

It is well known that a mirror shape of a single-beam reflector antenna that correctly reflects a radiation beam from a primary radiator in the same direction is a parabola.
In this case, the beams reflected at any mirror positions have the same path length, and the electric field phases on the plane (opening plane) perpendicular to the beam reflection direction match.

On the other hand, in the multi-beam antenna, since a plurality of beams share the same reflecting mirror, an error occurs in the electric field phase on the aperture surface depending on the beam direction. The fact that the phase of the aperture electric field is disturbed means that there is a beam component reflected in a direction other than the desired beam direction, which significantly degrades the antenna directivity.

In order to actually determine the aperture electric field, it is sufficient to know how the electromagnetic wave radiated from the primary radiator is reflected by the mirror surface of the antenna, and usually, it is determined by physical optics approximation. The physical optics approximation is a method of approximately obtaining a current distribution generated on an antenna mirror surface by an electromagnetic wave radiated from a primary radiator, and obtaining a radiation electromagnetic field generated by the current.

[0008] However, since the physical optics approximation requires a large amount of calculation, the geometrical optics approximation is used to more easily obtain the aperture plane electric field. The geometric optics approximation is a technique of assuming that the wavelength of the electromagnetic wave is negligible with respect to the size of the antenna structure, and that the electromagnetic wave is optically reflected by an antenna mirror surface.

[0009]

The contour of the reflector is determined so that the spillover power is reduced. However, unlike a single beam antenna, a multi-beam antenna has a plurality of beams sharing the same reflector. Therefore, there is essentially a specular aberration (path difference due to a difference in the reflection position on the specular surface).

[0010] For this reason, not all of the irradiation beam from the primary radiator is reflected in the desired direction, and the mirror profile that minimizes spillover is not necessarily the mirror profile that improves the radiation beam directional characteristics.

Further, the irradiation beam from the primary radiator, which irradiates a portion of the mirror surface having a large aberration, deteriorates the directivity and not only increases the side lobe level but also decreases the antenna gain. Note that the phase error of the aperture electric field due to specular aberration increases as the antenna aperture diameter and the beam radiation angle range increase.

In the prior art, although there is a specular aberration at each position of the reflecting mirror, this is not taken into account. Therefore, when the influence of the specular aberration cannot be ignored, the beam convergence performance deteriorates. , The side lobe characteristic is greatly deteriorated.

As described above, in the conventional multi-beam antenna, since the influence of specular aberration is not sufficiently considered, there is a problem that side lobe characteristics are greatly deteriorated when the antenna aperture diameter or the beam radiation angle range is large. there were.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-beam antenna capable of improving side lobe characteristics and having good directional characteristics over a wide range in order to solve the conventional problems as described above.

[0015]

According to the present invention, the above-mentioned object is solved by the means described in the claims.

That is, a first aspect of the present invention is a multi-beam antenna having a reflector and radiating beams in a plurality of directions from one antenna.

A plane perpendicular to the beam direction is defined as an aperture plane, an electric field distribution at the aperture plane is defined as an aperture electric field distribution, and a phase corresponding to one point of the reflecting mirror in the aperture plane electric field distribution is defined as a reference phase.
When the deviation between the phase of the aperture electric field distribution and the reference phase is defined as the aperture phase deviation,

At each point on the surface forming the reflecting mirror surface, the corresponding phase deviation of the aperture surface is weighted and averaged for each beam direction, and this value is obtained for the entire surface forming the reflecting mirror surface to draw a contour line.
This is a multi-beam antenna having a reflector whose contour is determined along the contour lines obtained here.

According to a second aspect of the present invention, there is provided a multi-beam antenna which has a reflector and emits a beam from one antenna in a plurality of directions.

The plane perpendicular to the beam direction is the aperture plane, the electric field distribution at the aperture plane is the aperture electric field distribution, and the phase of the vector sum of the aperture electric field is the reference phase. When the deviation from the phase is defined as the aperture phase deviation,

The product of the magnitude of the electric field amplitude of the aperture surface and the phase deviation of the aperture surface at a point on the surface forming the reflecting mirror surface is weighted averaged for each beam direction, and this value is obtained for the entire surface forming the reflecting mirror surface. This is a multi-beam antenna having a reflecting mirror that draws contour lines and determines contours along the contour lines obtained here.

According to a third aspect of the present invention, in the multi-beam antenna according to the first or second aspect, a radio wave absorber is attached to at least a part of a periphery of a reflecting surface of the reflecting mirror to substantially realize the reflecting mirror. The configuration is such that the contour line of the reflective surface is the contour line of the reflecting mirror.

[0023]

The conventional method of designing the mirror surface profile is to minimize the irradiation beam from the primary radiator that spills over from the reflecting mirror, and does not consider the difference in beam convergence performance at each mirror surface position. .

Therefore, the beam is also irradiated from the primary radiator to the mirror surface portion having low beam convergence performance (large phase error), and the influence of the mirror surface aberration such as when the antenna aperture diameter or the beam radiation angle range is large. Is not negligible, the convergence of the beam deteriorates, and the side lobe characteristics deteriorate.

FIG. 2 and FIG. 3 show contour lines of the aperture plane phase deviation distribution in the case of a beam direction of 0 degree B and in the case of 20 degrees, respectively, in a multi-beam antenna assuming an angle range of ± 20 degrees in the beam direction. FIG. The mirror surface of the antenna is a bifocal parabolic mirror surface, and the mirror surface coordinates are represented by an average value of two parabolas having different mirror axis directions.
(Refer to the literature "Kondo, Kagoshima, and Higa," Mirror design of multifocal parabolic antenna, "1992 IEICE Fall Autumn, B-53.)

The focal point of the bifocal parabolic mirror is YZ.
It exists in the plane, the focal length is 60λ, and the angle between the mirror axes of the two parabolas is 40 degrees. For this reason, power is supplied from the defocus position except when the beam direction is ± 20 degrees. The beam direction of the antenna is Y
-Parallel to the Z plane.

In obtaining the phase deviation in FIGS. 2 and 3, the mirror opening area is X = 0 to 44λ, Y = −34λ to 34.
λ, and the phase value at the position X = 16λ, Y = 0 was used as a reference. The coordinate values on the horizontal axis and the vertical axis are the X-axis and Y-axis coordinate values of the corresponding reflecting mirror position.

The phase deviation Δφ (X, Y) is equal to the optical path length L
It can be obtained geometrically using (X, Y), and in this case, it is expressed as "Equation 1".

[0029]

(Equation 1)

The optical path length L (X, Y) is the distance from the beam radiated from the primary radiator (feed point) to the aperture surface after being reflected by the antenna mirror at the position X = X, Y = Y. . L (X, Y) -L (16λ, 0) is the difference between the optical path length at the position used as the phase reference and the optical path length at the position of interest, and the phase deviation Δφ ( X, Y) is obtained by multiplying the difference between the optical path lengths by 2π / λ.

As shown in FIGS. 2 and 3, in the multi-beam antenna using the bifocal parabolic mirror surface, it can be seen that the contour line of the aperture phase deviation distribution differs depending on the beam direction.

Generally, the distribution shape of the phase deviation of the aperture plane differs depending on the beam direction except for the case of a torus mirror surface.
Further, in a multi-beam antenna that performs offset feeding, the conventional mirror surface profile determined so as to minimize the power spilling over from the reflector usually differs greatly from the contour shape of the aperture plane phase deviation.

In the multi-beam antenna according to the first aspect, a phase corresponding to one point of the reflector in the aperture electric field distribution is set as a reference phase, and a deviation between the phase of the aperture electric field distribution and the reference phase is defined as an aperture phase deviation. The most characteristic feature is that the contour of the reflector is determined from the contour line of the weighted average value of the phase deviation of the aperture plane at the corresponding reflector position in each beam direction. With this configuration, the irradiation beam from the primary radiator can preferentially use a mirror surface portion having good convergence performance.

In the multi-beam antenna according to the present invention, the phase of the sum of the aperture electric fields in the aperture electric field distribution is used as a reference phase, and the contour of the reflector is the aperture electric field amplitude at the position of the corresponding reflector in each beam direction. The most significant feature is that it is determined from the contour line of the weighted average value of the product of the size of the aperture plane phase deviation. With this configuration, as for the irradiation beam from the primary radiator, it is possible to preferentially use a mirror surface portion having small aberration and good convergence performance in each beam direction.

As described above, the multi-beam antenna of the present invention preferentially uses the mirror surface contour of the reflecting mirror for the mirror surface portion having good beam convergence performance, so that the antenna aperture diameter and the beam radiation angle range are large. Even when the influence of specular aberration cannot be ignored, for example, it is possible to suppress the deterioration of the directivity and side lobe characteristics. Further, by mainly improving the directional characteristics in an arbitrary direction, a multi-beam antenna having good directional characteristics over a wide range can be realized.

The method according to claim 1 and the method according to claim 2
In both of the methods described in (1) and (2), in the case of a high-efficiency antenna having a relatively small antenna aperture diameter, almost the same reflecting mirror contour shape can be obtained. However, the method of claim 1 has a small amount of calculation and is simple. However, in the case where the antenna aperture diameter is large and the irradiation area from the primary radiator to the reflecting mirror is largely different depending on the beam direction, the method of claim 2 in which the directional characteristics of the primary radiator are also taken into account gives better results. .

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the present invention is applied to a wide-angle multi-beam antenna will be described below. The beam direction of the antenna was continuously -20 to 20 degrees, and the reflecting mirror was a bifocal parabola with a focal length of 60λ.

FIG. 4 shows beam directions of 0 degree, ± 5 degrees, ± 10 degrees.
The contour lines of the weighted average value of the aperture plane phase deviation distribution in the case of degrees, ± 15 degrees, and ± 20 degrees are shown. This is because each beam direction θ (θ = 0 degree, ± 5 degrees, ± 10 degrees, ± 15 degrees)
(± 20 degrees), the phase deviation Δφθ (X, Y) at the corresponding mirror position (X, Y) is obtained, and the weighted average is calculated for each beam direction. Is represented by

[0039]

(Equation 2)

It can be seen from the contour lines shown in FIG. 4 that the lower part of the reflecting mirror has less phase deviation as a whole than the upper part.
Therefore, if the mirror surface contour diverging along the contour line of the phase deviation distribution in FIG. 4 is adopted by the method of claim 1, the beam convergence performance can be improved.

The contour of the mirror surface obtained by using contour lines having a phase deviation of about 40 degrees and adjusting the lower portion of the reflecting mirror to avoid blocking by the primary radiator is as shown by numeral 5 in FIG. In FIG. 5, a solid line indicated by reference numeral 5 is a mirror surface profile of the antenna of the present invention, and a dotted line indicated by reference numeral 4 is a mirror surface profile according to the prior art determined to minimize spillover, and both have the same opening area. It is like that.

It should be noted that the method according to the second aspect also provides substantially the same contour as that obtained by the method according to the first aspect. FIG.
FIG. 3 illustrates a mirror surface profile obtained by the method of claim 2, and shows a contour line of a weighted average of a product of a magnitude of an electric field amplitude of an aperture surface and a phase deviation of the aperture surface.

In FIG. 7, the half width of the irradiation beam from the primary radiator is assumed to be 17 degrees. The values of the contour lines in this figure increase in the order indicated by a, b, c, and d. From this, it can be confirmed that the contour interval in the region where the irradiation beam from the primary radiator does not hit much is widened, but the divergent contour shape is obtained as in FIG.

FIG. 6 is a diagram comparing the directivity characteristics of the antenna of the present invention and the conventional antenna, and FIG.
The solid line and the dotted line shown in (c) show the directional characteristics of the antenna of the present invention and the conventional antenna when the beam directions are 0 degree, 10 degrees, and 20 degrees, respectively. As shown in the figure, the antenna according to the present invention can significantly improve the side lobe characteristics without deteriorating the gain as compared with the conventional antenna.

In the present invention, the directional characteristics in an arbitrary direction can be mainly improved by appropriately selecting the weighting factor when obtaining the contour line of the weighted average value of the aperture plane phase deviation distribution.

Also, when the radio wave absorber is stuck on the reflecting mirror surface (for example, the left and right ends of the reflecting mirror surface) and the mirror opening is adjusted, the radio wave absorber is stuck along the mirror surface contour of the antenna according to the present invention. By doing so, the same effect as when the contour shape of the reflecting mirror itself is set according to the present invention can be obtained.

[0047]

As described above, the multi-beam antenna of the present invention preferentially uses the mirror surface portion having good beam convergence performance, so that the influence of the mirror surface aberration is large when the antenna aperture diameter or the beam radiation angle range is large. Can not be neglected, it is possible to suppress deterioration of the directional characteristics and the side lobe characteristics. In addition, it is possible to provide a multi-beam antenna having good directional characteristics over a wide range by mainly improving directional characteristics in arbitrary directions.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a configuration of a multi-beam antenna.

FIG. 2 is a diagram illustrating an example of contour lines of an aperture plane phase deviation distribution of a multi-beam antenna.

FIG. 3 is a diagram illustrating an example of contour lines of an aperture plane phase deviation distribution of a multi-beam antenna.

FIG. 4 is a diagram illustrating an example of contour lines of a weighted average value of an aperture phase deviation distribution of a multi-beam antenna.

FIG. 5 is a diagram showing an example of the contour of the reflector of the antenna of the present invention.

FIG. 6 is a diagram comparing the directional characteristics of the antenna of the present invention and a conventional antenna.

FIG. 7 is a diagram illustrating an example of contour lines of a weighted average value of an electric field amplitude and a phase deviation distribution of an aperture plane of an aperture plane of a multi-beam antenna.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reflector 2a, 2b, 2c Primary radiator 3a, 3b, 3c Trajectory of the beam emitted from the primary radiator 4 Mirror surface profile according to the prior art 5 Mirror surface profile according to the present invention

Continuation of the front page (72) Inventor Hideki Mizuno Nippon Telegraph and Telephone Corporation, 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo (56) References JP-A-8-228108 (JP, A) JP-A-8-237023 (JP, A) JP-A-5-152835 (JP, A) Akira Kondo, Kenichi Kagoshima, Hidemitsu Higa, Mirror design of multifocal parabolic antenna, 1992 IEICE Autumn Conference, Japan, Japan Association The Institute of Electronics, Information and Communication Engineers, September 15, 1992, Volume 2, B-53 Fumio Kira, Kohei Ohata, Hideki Mizuno, Study of Cluster-Fed Wide-Angle Multibeam Antenna-One Method of Mirror Surface Design-, Electronic Information Communication Proceedings of the General Conference of the Society, Japan, The Institute of Electronics, Information and Communication Engineers, March 10, 1995, Communication 1, B-136 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01Q 1/00 H01Q 3/26 H01Q 15/16 H01Q 19/17

Claims (3)

(57) [Claims] 1. A multi-beam antenna having a reflector and radiating beams from one antenna in a plurality of directions. A plane perpendicular to the beam direction is defined as an aperture plane, and an electric field distribution in the aperture plane is defined as an aperture plane electric field distribution. When the phase corresponding to a certain point of the reflector in the electric field distribution is defined as a reference phase, and the deviation between the phase of the aperture electric field distribution and the reference phase is defined as the aperture phase deviation, the aperture corresponding to the point on the surface forming the reflection mirror surface Surface phase deviation is weighted averaged for each beam direction, this value is obtained for the entire surface forming the reflecting mirror surface, contour lines are drawn, and a reflecting mirror whose contour is determined along the contour lines obtained here is characterized by having Multi-beam antenna. 2. A multi-beam antenna having a reflector and radiating beams from one antenna in a plurality of directions, wherein a plane perpendicular to the beam direction is an aperture, an electric field distribution in the aperture is an aperture electric field distribution, an aperture When the phase of the vector sum of the aperture plane electric field in the electric field distribution is defined as the reference phase, and the deviation between the phase of the aperture plane electric field distribution and the reference phase is defined as the aperture plane phase deviation, the corresponding aperture plane at a point on the surface forming the reflecting mirror surface The product of the magnitude of the electric field amplitude and the phase deviation of the aperture plane is weighted averaged for each beam direction, and this value is obtained for the entire surface forming the reflecting mirror surface to draw a contour line, and the contour is drawn along the contour line obtained here. A multi-beam antenna having a determined reflector. 3. The reflector according to claim 1, wherein a radio wave absorber is attached to at least a part of the periphery of the reflecting surface of the reflecting mirror, and a substantial contour of the reflecting surface of the reflecting mirror is used as a contour of the reflecting mirror. Item 2. A multi-beam antenna according to Item 2.