JPS6251002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic horn, and particularly to an electromagnetic horn suitable for constructing a multi-beam circularly polarized antenna.

In general, the service areas of broadcasting satellites and communication satellites often have complex shapes.
When looking at Japan from a geostationary satellite orbit on the equator at 110 degrees east longitude, the service area looks like the shape shown in Figure 1. Therefore, as an antenna that efficiently covers such a complex-shaped service area, it is better to combine multiple antenna beams to cover the service area described above, rather than an antenna that forms a single elliptical beam. A multi-beam shaped beam antenna that forms a beam pattern that fits a complex shape is more suitable. For example, in the case where a three-beam shaped beam antenna that combines three electromagnetic horns and a parabolic reflector covers a service area with the shape shown in Figure 1, the operation of the shaped beam antenna will be explained in the second section. An example of the basic configuration of such a shaped beam antenna is shown in FIG.

In the operational mode of the shaped beam antenna shown in Fig. 2, the first electromagnetic horn that forms the main antenna beam broadly covers the service area A that covers the mainland of Japan, and the second and third electromagnetic horns cover the Okinawa area. Service area B covers the area and service area C covers the Ogasawara area.
It is designed to cover each. In the schematic configuration shown in FIG. 3 of an antenna configured to form such a shaped beam, a main beam of each of the above-mentioned electromagnetic horns as a primary radiator is placed at a focal point F on the axis of a parabolic reflector T. A first electromagnetic horn 1 is arranged with the center of its aperture aligned with a focal point F, and a second electromagnetic horn, for example, is placed off-axis with respect to the parabolic reflector T and placed at a point Q near the focal point F. 2 are arranged, and these electromagnetic horns 1 and 2 are combined with a parabolic reflector T.
Regarding the direction of the antenna beam from the antenna with such a configuration, the direction of the antenna beam from the first electromagnetic horn 1 placed on the axis of the reflector T is the R ₀ direction, which coincides with the axial direction of the reflector T. The direction of the antenna beam from the second electromagnetic horn 2 placed off-axis with respect to T is the R direction shown in the figure, which connects the center M of the parabolic reflector T and the point Q where the second electromagnetic horn 2 is placed. The angle α between the line and the R ₀ direction is approximately equal to the angle β between the R ₀ direction and the R direction. Although not shown in the figure, like the second electromagnetic horn 2, a parabolic reflector T
The same holds true for the third electromagnetic horn 3, which is arranged off-axis.

When the shape distribution of the service areas to be covered by the shaped beam antennas configured and arranged as described above is determined, for example, as in the service areas A, B, and C shown in the second diagram, first, it is necessary to cover the main service area A. If the direction R ₀ of the antenna beam by the first electromagnetic horn 1 arranged on the power axis, that is, the axial direction of the reflector T, is directed to the center of the service area A, it is possible to connect the service areas A and B from the above-mentioned geostationary satellite orbit. By making it equal to the viewing angle, the angle β between the R ₀ direction and the R direction mentioned above is determined, and therefore, the angle α equal to the angle β is determined.
is decided. On the other hand, since the distance MF between the center M of the reflecting mirror T and the focal point F in the configuration shown in FIG. From α, the second
The distance QF between the off-axis point Q and the focal point F at which the electromagnetic horn 2 is to be placed is determined. Therefore, the position of the off-axis point at which the accompanying electromagnetic horn that forms the sub-beam should be placed is uniquely determined by the shape distribution of the service area.

However, regarding the polarization format of microwaves transmitted from broadcasting satellites, it is generally preferable to use circularly polarized waves, mainly for the convenience of adjusting the arrangement of receiving antennas in receiving devices that general viewers must install individually. However, the diameter of the cone-shaped electromagnetic horn suitable for emitting such circularly polarized microwaves, that is, the diameter of the circle forming the opening of the conical horn, is the parabolic type that is arranged opposite to the conical horn and combined. In order to efficiently irradiate the total reflection surface of the reflecting mirror with the conical horn, it is necessary to have a constant size determined by the shape and dimensions of the reflecting mirror.
When multiple conical horns are to be arranged as shown in Figure 3, the distance QF between the off-axis point Q and the focal point F needs to be set smaller than the aperture diameter of each conical horn. If the conical horn is used, it is impossible to construct a multi-beam shaped beam antenna that should cover the required service area.

To summarize what has been said above, multi-beam shaped beam antennas for broadcasting satellites that cover service areas with complex shape distributions use a composite primary radiator that should be placed opposite a parabolic reflector. The constituting electromagnetic horn is an electromagnetic horn having apertures of a shape that can be arranged in close proximity and combined as desired, and is also capable of circularly polarized wave excitation consisting of a combination of two orthogonal polarized wave components. It is preferable and necessary that
Conical horns, which are electromagnetic horns that can excite circularly polarized waves, have been conventionally used in such cases, but are limited by their aperture diameters, so it is difficult to efficiently cover a service area with a desired shape distribution by combining multiple conical horns. The disadvantage was that it was difficult to construct a shaped beam antenna that could be used.

On the other hand, an electromagnetic horn for a primary radiator that constitutes a circularly polarized antenna essential for broadcasting satellites and the like is required to have a radiation pattern as symmetrical as possible.
In other words, a circularly polarized antenna is synthesized by combining two linearly polarized antennas, each excited by linearly polarized waves of the same frequency and amplitude, whose polarization planes are orthogonal to each other and have a phase difference of 90 degrees. It can be considered as having been done. Therefore, if the irradiation pattern of the electromagnetic waves that irradiate the parabolic reflector is not the same when the electromagnetic wave that excites the electromagnetic horn as the primary radiator is vertically polarized and when it is horizontally polarized, the parabolic reflector Since the gain in directions other than boresight is determined by the irradiation pattern of the primary radiator that irradiates it, circularly polarized waves cannot be obtained in this direction. If the gain in directions other than the boresight of the reflector is not equal for vertically polarized waves and horizontally polarized waves, then the amplitude of the two orthogonal polarization components of the electromagnetic wave reflected by the reflector and radiated will be are different from each other, and even if these two orthogonal polarized components are combined, circularly polarized waves will not be obtained in this direction. However, the radiation patterns of the electromagnetic waves radiated by the conventional square horn having a square aperture or the conical horn having a circular aperture are significantly different from each other between the electric plane, that is, the E plane, and the magnetic plane, that is, the H plane. However, the E-plane radiation pattern attenuates much more rapidly than the H-plane radiation pattern as the deflection from the axis increases, that is, the off-axis angle increases, resulting in a much steeper irradiation pattern. As an example, the E of a conical horn with an aperture diameter of 4 cm at 12 GHz is
The radiation patterns of the plane and the H plane are shown in FIG.

There are corrugated horns, compound mode horns, and dielectric-loaded horns that aim to achieve symmetry in the radiation pattern of horns, but none of them are suitable for use on satellites due to their aperture size, weight, and bandwidth. .

The object of the present invention is to solve the above-mentioned conventional problems and eliminate the drawbacks, and to provide a multi-beam for use on a satellite that can cover a service area exhibiting any desired shape distribution by arranging a plurality of beams in close proximity and combining them. An object of the present invention is to provide an electromagnetic horn which is suitable for constructing a type of shaped beam antenna and which can easily obtain substantially the same radiation pattern on the E plane and the H plane.

That is, the electromagnetic horn of the present invention has at least the following:
A plurality of unit electromagnetic horns each having an aperture in the shape of a substantially square shape in which the corner portions of the square are substantially equal to each other and each cut out, and an opening similar to the cut out corner portion of the aperture of the electromagnetic horn of the unit are arranged. The present invention is characterized in that a composite electromagnetic horn is constructed by arranging openings of other units of electromagnetic horns having the same shape.

The invention will be explained in detail below by way of example embodiments with reference to the drawings.

First, FIG. 5 shows an example of the basic shape of the aperture and the electric field distribution within the aperture in the electromagnetic horn of the present invention. The opening of the electromagnetic horn shown in FIG. 5 has the shape of a square whose side length is (a+2b), with four corners cut out and removed into a square shape whose side length is b. The electric field distribution of the fundamental wave in the TE mode electromagnetic waves generated in the shaped aperture can be solved by replacing Maxwell's equation with a difference equation, and based on the electric field distribution, the electromagnetic wave having the shaped aperture can be determined. The radiation pattern of the horn can be determined. Note that the wavelength of the fundamental wave of the TE mode generated in the aperture having the shape shown in Figure 5 is the length of one side (a+
2b) is approximately equivalent to that of a circular opening having a diameter appropriately shortened according to the ratio of the length b of one side of the cut square shape, and therefore, the opening has the shape shown in Figure 5. The propagation mode of electromagnetic waves is almost the same as that of a circular aperture equivalent to the average shape of its periphery.

Therefore, for the radiation pattern of an electromagnetic horn having an aperture shaped as shown in Figure 5, the ratio a:b of the length a of the remaining part of one side of the basic square to the length b of one side of the cut square shape is determined. By changing the ratio, the manner in which the radiation patterns differ between the E-plane and the H-plane changes, and when a:b=2:1, the radiation patterns of the E-plane and the H-plane become almost the same.

As an example of the matching of the radiation patterns between the E plane and the H plane due to the above-mentioned shape and size of the aperture of the electromagnetic horn of the present invention, the assigned frequency of microwave for satellite broadcasting is shown.
FIG. 6 shows an example of calculation of radiation patterns in the E plane and H plane at a frequency of 12 GHz when a:b=2:1 for an aperture having the shape shown in FIG. 5 in an electromagnetic horn configured for 12 GHz. Each of the radiation pattern curves shown in Figure 6 agrees well with the actual measurement values, and as is clear from comparing each of the curves shown, even if the basic square is the same, each corner of the curve is Depending on whether or not the E-plane is cut into a square shape, the radiation pattern on the E-plane changes significantly, whereas the radiation pattern on the H-plane hardly changes. can be considered to be almost the same as the radiation pattern of the E plane when cut out. Therefore, for the shape of the electromagnetic horn according to the present invention shown in FIG. 5, approximately a:b=
If the ratio is 2:1, circularly polarized waves can be radiated with a substantially satisfactory radiation pattern.

FIG. 7 shows an example of a configuration in which a circularly polarized wave excitation is performed on an electromagnetic horn for circularly polarized wave radiation, which provides a good radiation pattern as described above. In the circularly polarized wave excitation electromagnetic horn shown in FIG. The cylindrical waveguide section with a circular cross section is connected to the circularly polarized wave generator 5.
The excitation linear polarized wave is converted into a circularly polarized wave by connecting the two orthogonal polarized wave components to a 90-degree delay in the phase of one of the two orthogonal polarized wave components. The circularly polarized wave generator 5 is connected to the electromagnetic horn 1 of the present invention having an opening shaped as shown in FIG. Excite.

Next, a three-beam circularly polarized antenna is constructed by combining three electromagnetic horns of the present invention having the same shape and dimensions. A composite beam antenna composite in which the angle cut portions of the apertures of each electromagnetic horn are combined with each other so that the angle formed with each other in the direction of directivity is the narrowest, and the distance between the centers of each aperture is the shortest. An example of the structure of the electromagnetic horn is shown in FIG. In the configuration shown in FIG. 8, the opening center spacing of the second and third electromagnetic horns 2 and 3 combined with each corner of the first electromagnetic horn 1 is a square opening when the corner is not cut. is the same as the aperture center spacing of
The aperture center spacing between each electromagnetic horn 2 and 3 and the electromagnetic horn 1 is narrowed by the length b where the corners of the basic squares of each electromagnetic horn overlap. The distance between the multi-beams obtained when the three electromagnetic horns of the present invention combined as shown in Figure 8 are combined with a parabolic reflector, that is, the angle of orientation of each beam, is as described above. Ratio of aperture center spacing with and without corner resection Since a = 2b at , the width can be narrowed by about 20%.

Next, as shown in Figure 2, if there is a significant difference in width between the three service areas A, B, and C that should be covered by the 3-beam antenna, the narrower service areas B and C should be used. In order to sharpen the reflected beam from the parabolic reflector covering the area, and to efficiently focus the reflected beam by irradiating the entire surface of the reflector, It is necessary to spread the irradiation beam, and therefore the aperture area of these electromagnetic horns itself needs to be much smaller than the aperture area of the main electromagnetic horn 1. FIG. 9 shows an example of the configuration of the opening of the primary radiator for a three-beam antenna according to the present invention in such a case. Note that the distance between the aperture centers can be narrowed by arranging the side of the aperture parallel to the side of the main aperture for the auxiliary electromagnetic horn to be arranged in combination with each corner cut portion of the aperture of the main electromagnetic horn 1. Although the aperture can have an arbitrary shape, it is preferable to use a shape similar to the main aperture according to the present invention as long as circularly polarized radiation is performed. In this case, the narrow angle in the directivity direction of the main and sub beams can be made narrower by about 15% compared to the case where both the main and sub apertures are square.

As is clear from the above explanation, by using the electromagnetic horn of the present invention as the primary radiator of a circularly polarized antenna, it is possible to irradiate the parabolic reflector with almost the same pattern for two orthogonal polarized components. , a circularly polarized antenna with good performance can be constructed. Further, the electromagnetic horn of the present invention has a simple aperture shape, and constitutes a multi-beam circularly polarized antenna in which a plurality of electromagnetic horns must be arranged in combination with their aperture centers as close as possible to each other. At times, with the electromagnetic horn of the present invention, the spacing between each beam can be reduced by about 20%.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the shape distribution of the service area of a broadcasting satellite, Fig. 2 is a diagram showing an example of the operation mode of a multi-beam antenna that covers the service area shown in Fig. Similarly, FIG. 4 is a diagram schematically showing an example of the configuration of the multi-beam antenna, FIG. 4 is a diagram showing an example of the radiation pattern of a conventional conical horn, and FIG. 5 is an example of the aperture configuration and electric field distribution of the electromagnetic horn of the present invention. FIG. 6 is a diagram showing an example of the radiation pattern, FIG. 7 is a perspective view showing an example of the configuration of a circularly polarized excitation electromagnetic horn according to the present invention, and FIG. 8 is a diagram showing an example of the radiation pattern according to the present invention. FIG. 9 is a diagram showing an example of the configuration of the aperture of a primary radiator for a multi-beam circularly polarized antenna, and FIG. 9 is a diagram showing another example of the configuration. 1, 2, 3... Electromagnetic horn, 4, 6... Square-cylindrical conversion tube, 5... Circularly polarized wave generator, 7... Square-square converter, 8... Rectangular waveguide, T... Parabolic reflector, M...center, F...focal point, Q...
Off-axis point.

Claims (1)

[Scope of Claims] 1. At least a plurality of unit electromagnetic horns each having an opening shaped like a substantially square corner cut out from each other, each corner of a square being substantially equal to each other, each of which has an opening of the unit electromagnetic horn. An electromagnetic horn characterized in that a composite electromagnetic horn is constructed by combining and arranging openings of other units of the electromagnetic horn having opening shapes similar to the cut corner portions. 2. The electromagnetic horn according to claim 1, wherein the length of one side of the square shape is approximately equal to 1/4 of the length of one side of the square.