JPH047123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a primary radiator that is combined with a reflecting mirror to constitute a parabolic antenna.

The aperture efficiency of conventional parabolic antennas is 45 to 65%.
In order to improve the aperture efficiency, it is said that the smaller the aperture angle is, the more advantageous it is, but the smaller the aperture angle, the lower the F/S (front ratio) and F/B (front/back ratio).
The aperture angle cannot be reduced unnecessarily because the characteristics will deteriorate.

The aperture efficiency also depends on the non-uniformity of the aperture illuminance distribution, the phase difference, the leakage radiation in which the electromagnetic waves from the primary radiator are radiated directly into space without hitting the reflecting mirror, the support member used to fix the primary radiator at the focal point, etc. It decreases due to scattering by waveguides, etc., deviation from the focus of the primary radiator, dimensional error of the reflector, etc., and is about 50 to 55% for a typical parabolic antenna.

Furthermore, there is a small horn antenna that is used as the primary radiator of a parabolic antenna, but unlike a general horn antenna, this horn antenna requires an optimal directivity for the aperture angle of the parabolic antenna. The opening dimensions, axial length, etc. of As a result, the size of the horn becomes as small as the wavelength, and F/S, F/
There was a drawback that the B characteristic and gain were reduced.

Conventionally, two horn antennas are used as the primary radiator to prevent such drawbacks, but this requires two horn antennas and a distributor, which increases the cost and also requires two support members and two horn antennas. Because the electromagnetic waves are blocked by the horn antenna and the gain is reduced, the effect cannot be fully demonstrated unless it is an offset type parabolic antenna.

This invention is a horn antenna that is a primary radiator, and the axis of the primary radiator is located at a position approximately λ/4 (λ is the wavelength of the radio waves radiated by the primary radiator) behind the opening edge of the horn antenna. By providing a secondary horn that extends toward the parabolic reflector at an angle larger than the aperture angle of the horn antenna and smaller than 90°, the aperture illuminance distribution and leakage radiation are improved and the aperture efficiency is increased. be.

The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a diagram schematically showing a horn antenna which is a primary radiator embodying the present invention. In the figure, 1 is a waveguide.

A flange portion 2 is provided at the end of the waveguide 1,
A horn antenna 3 is fixed to this flange portion 2 with screws 4. The horn antenna 3 has an approximately cylindrical or prismatic outer shape, and a horn 5 having an aperture angle θ is formed inside.

A sub-horn 6 is attached at a position facing from the opening edge of the horn antenna 3 toward the waveguide 1 by λ/4 (λ is the wavelength of the electromagnetic wave emitted by the horn antenna 3). The sub-horn 6 has a pyramidal or conical shape in accordance with the shape of the horn antenna 3, and its opening angle φ is about 45°.

The primary radiator 10 of the parabolic antenna configured in this way is placed on the focal point of the parabolic reflector 11 via the waveguide 1, as shown in FIG.

Next, from this primary radiator 10 to the parabolic reflector 1
The electromagnetic waves radiated to 1 will be explained.

Most of the electromagnetic waves radiated from the horn antenna 3 head toward the parabolic reflector 11 as main radiation A, B, and C as shown in FIG. ′,
The light is radiated to areas other than the parabolic reflector 11 as B' and C'.

Among these leakage radiations A', B', and C', the main radiation A in the axial direction and the leakage radiation A' in the opposite direction are from the secondary horn 6.
However, at this time, the phase is opposite to that of the main radiation A, weakening the electric field of the main radiation A. However, in general, the main radiation A is sufficiently larger than the leakage radiation A', and furthermore, the main radiation A is a part that requires a vertex matching plate, etc.
Moreover, since it is a part that is reflected by the power feeding waveguide 1 or becomes a shadow, and its area is small, the aperture efficiency does not decrease.

If there is no sub-horn 6, the leakage radiation B' will be emitted outside the parabolic reflector 11 and deteriorate the F/S characteristics, but by attaching the sub-horn 6, the leakage radiation B' will be emitted from the parabolic reflector as an electromagnetic wave parallel to the main radiation B. Head to 11. At this time, the phase difference of leakage radiation B' with respect to B is
It is located in the 0° direction rather than 90° and is added to the electric field of the main radiation B. The phase difference relationship between leakage radiation C′ and radiation C is
The phase difference is smaller than that of B and B' mentioned above, and they approach the same phase, and C and C' form an added electric field. These B, B', C, and C' are close to the outer periphery of the parabolic reflector 11 and have the same angular width as the main radiation A, but their total radiation area is large, so they increase the aperture efficiency even if the added electric field is small. . Furthermore, since radiation in directions wider than the D direction is blocked by the sub-horn 6, leakage radiation to the outside from the parabolic reflector 11 seen from the horn is reduced. In this way, the radio waves that were conventionally emitted to areas other than the parabolic reflector 11 are reflected at the peripheral edge of the sub-horn 6, and the radio waves are emitted to areas other than the parabolic reflector 11.
Therefore, the number of radio waves directed toward the outer peripheral surface of the parabolic reflector increases, and the illuminance distribution becomes uniform.

FIG. 3 shows the directional characteristics 12 of the composite primary radiator according to the present invention and the directional characteristics 14 of a conventional primary radiator without an auxiliary horn. In the figure, the reason that the directivity of the composite primary radiator according to the present invention is worse than that of the conventional one near 0° is because the phase difference between the main radiation A and the leakage radiation A' is 180°. In the vicinity of ±20° to ±40°, the composite primary radiator according to the present invention has a directivity similar to that of the conventional one.

Figure 4 shows the directional characteristics 16 when a composite primary radiator according to the present invention is attached to a 75 cm parabolic reflector 11, and the directional characteristics 16 when a conventional primary radiator without a secondary horn is attached to the same reflector 11. 18 is shown. In the same figure, in the 0° direction, when the composite primary radiator according to the present invention is installed, the antenna gain is approximately 1 dB higher than when the conventional primary radiator is installed, and the overall direction is Sexuality is becoming more acute.

Figures 5 to 7 show a 75cm parabolic reflector 1.
1 shows the change in gain when the composite primary radiator according to the present invention is attached and the attachment position, aperture angle, and diameter of the sub-horn 6 are changed. Figure 5 shows the case where the opening angle of the sub-horn 6 is 55°, the diameter of the sub-horn 6 is 80 mm, and the mounting position is changed, and the gain increases by approximately 1 dB at the positions indicated by points a and c in the figure. There is. The reason why the gain increases at the position of point c is that the sub-horn 6 is installed on the waveguide 1 side by l ₂ from the horn opening as shown in FIG. On the other hand, the radio waves that hit the secondary horn 6 and were reflected
This is because F' passes through egh and this distance is longer than ef by λ, so F and F' are in phase. Note that the distance difference between points b and d is approximately 1/2λ, which is F
and F' are in opposite phase, so the gain is reduced.

Figure 6 shows the case where the distance from the horn opening of the sub-horn 6 is λ/4, the diameter of the sub-horn 6 is 80 mm, and the opening angle of the sub-horn 6 is changed, and the opening angle is 55°.
The gain is maximum when . Note that this opening angle φ
is greater than or equal to the horn opening angle θ and relative to the central axis.
It has been found that a angle of 90° or less (see Figure 1) is sufficient for practical use.

FIG. 7 shows a case where the distance from the horn opening of the sub-horn 6 is λ/4, the aperture angle of the sub-horn 6 is 55°, and the diameter of the sub-horn is varied, and the gain is maximum at 80 mm. The reason why the gain decreases when the diameter is increased to 80 mm or more is that when this parabolic antenna is used as a receiving device, when the received radio waves arrive at the parabolic reflector 11, the receiving radiator becomes large and its shadow becomes a mirror surface. This is because the radiator occupies a large area, and when used as a transmitter, the shadow of the radiator casts a shadow on the receiving area.

In addition, in the above embodiment, the sub horn 6 was formed into a conical shape or a square pyramid shape.
Various cross-sectional shapes can be used as shown in
Its wall thickness is independent of the performance of this composite primary radiator. In addition, in figure f, by adding the triangular part 20 to the attachment part of the sub-horn 6, the phase of the leakage radiation E' can be delayed by 2l with respect to the main radiation E.
As a result, the phase difference between E and E' is equal to A in Figure 1.
Since the angle is smaller and more acute than the phase difference (180°) with A', the sum of E and E' is larger than E,
The drop around 0° in Figure 3 is improved.

Further, in the above embodiments, the sub-horns 6 are provided all around the horn antenna 3, but the sub-horns may be provided only in a part of the periphery.

Furthermore, when the present invention is applied to an offset type parabolic antenna, the electromagnetic waves reflected from the parabolic reflector are not blocked by the sub-horn, so the diameter of the sub-horn can be increased and its effect can be increased.

As explained above, according to the present invention, the horn antenna, which is the primary radiator, is placed at a position behind the aperture edge of the horn antenna at a position larger than the aperture angle of the horn antenna with respect to the axis of the horn antenna, all around or in a part of the direction. By providing a secondary horn that extends toward the parabolic reflector at an angle smaller than 90°, the leakage radiation from the primary radiator is radiated toward the reflection side by the secondary horn, making this composite primary radiator When used with a parabolic reflector, F/S, F/B
It is possible to realize a parabolic antenna with good characteristics and aperture efficiency, and since this composite primary radiator has a simple configuration of a normal primary radiator with a secondary horn, it is easy to manufacture and is low cost. It is.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a composite primary radiator for a parabolic antenna according to the present invention, FIG. 2 is a partial vertical cross-sectional view of a parabolic antenna using this composite primary radiator, and FIG. 3 is a partial vertical cross-sectional view of a parabolic antenna using this composite primary radiator. Figure 4 shows the directivity characteristics of a parabolic antenna using this composite primary radiator and a conventional parabolic antenna using a primary radiator.
The figure shows the change in the gain of the parabolic antenna when the mounting position of the secondary horn of this composite primary radiator is changed, and Figure 6 shows the gain change of the parabolic antenna when the aperture angle of the secondary horn of this composite primary radiator is changed. Figure 7 is a diagram showing the gain change of the antenna. Figure 7 is a diagram showing the gain change of this parabolic antenna when the diameter of the secondary horn of this composite primary radiator is changed. Figure 8 is a diagram showing the gain change of this parabolic antenna when the diameter of the secondary horn of this composite primary radiator is changed. Figures 9a to 9f are diagrams for explaining the reason why the gain of the parabolic antenna changes depending on the mounting position of the parabolic antenna, and are diagrams showing modified examples of this composite primary radiator. 1... Waveguide, 3... Horn antenna, 6...
Secondary horn, 10...primary radiator, 11...parabolic reflector.

Claims (1)

[Claims] 1. A horn-shaped primary which is provided at the focal point of the parabolic reflector to face the parabolic reflector, and whose diameter decreases from the aperture edge toward the side opposite to the parabolic reflector to form a predetermined aperture angle. radiator, and the entire outer periphery of the primary radiator at a position approximately λ/4 (λ is the wavelength of the radio wave radiated by the primary radiator) on the opposite side from the parabolic reflector from the opening edge of the primary radiator. or a parabolic antenna comprising a sub-horn extending from a portion thereof toward the parabolic reflector at an angle larger than the aperture angle of the primary radiator and smaller than 90° with respect to the central axis of the primary radiator. Composite primary radiator for use.