JPS6022843B2 - antenna device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In order to improve the front-to-side radiation ratio and the front-to-back radiation ratio of wide-angle radiation characteristics in closed-surface antennas such as parabolic antennas and Cassegrain antennas, This relates to radio wave shielding that can be installed.

As a subsidiary device of this type, a radio wave shielding plate 2 is provided around the entrance of the reflecting mirror 1 as shown in FIG. 1a, and an unevenness is provided around the opening of the reflecting mirror 1 as shown in FIG. There was a type with metal fins 3. In FIG. 2, the radiated electric field on the sides and rear of the antenna is given by the radio waves from the primary radiator 5 hitting the green 4a of the reflector 1 or the radio wave shielding plate 2, and the diffracted waves from the green 4a. This diffraction wave pressure d is equal to the incident wave pressure at the edge 4a and the diffraction coefficient D
It is expressed by the following formula by a. Sho d = Da pressure i
'11 Here, Da<<1.

Therefore, by attaching the radio wave shielding plate 2 as shown in FIG. is smaller, so that the wide-angle radiation characteristics can be improved to some extent, but when trying to achieve relatively good characteristics, the width of the radio wave shielding plate 2 has to be increased.

Further, as shown in FIG. 1b, the wide-angle radiation characteristics are improved by making the phases of the diffracted waves from the green 4a of the reflecting mirror 1 and the diffracted waves from the edge 4a of the metal fin 3 opposite to each other. The method is based on the fact that the frequency band with relatively good characteristics is narrow,
There was a drawback in that it could not be improved in certain directions.
In order to eliminate these drawbacks, this invention provides radio waves with a straight or L-shaped cross section only in the area that is not directly hit by the radio waves radiated from the primary radiator, along the green area around the Sekiguchi of the closed antenna. By providing one or more shields in combination, the diffracted waves from the edge are prevented from propagating directly to the sides and rear of the antenna.
The drawings will be explained in detail below.

FIG. 3 shows an embodiment of the present invention, in which a diffraction wave shielding plate made of a metal plate, gold steel, or linear metal is placed outside the closed periphery of the reflecting mirror 1 or outside the periphery of the radio wave shielding plate 2. 6 prevents the diffracted waves from the edge 4a of the reflecting mirror 1 or the edge 4a of the radio wave shielding plate 2 from propagating directly to the sides and rear of the antenna.

That is, the radio wave propagated from the primary radiator 5 to the green 4a of the reflecting mirror 1 is diffracted by the green 4a and wraps around the hair surface of the reflecting mirror 1. Here, by providing the diffracted wave shielding plate 6 in a shaded area where the radio waves from the primary radiator 5 do not directly hit, the incident wave at the edge 4b of the diffracted wave shielding plate 6 is caused by diffraction from the edge 4a of the reflecting mirror 1. Therefore, the diffracted wave from the green 4b of the diffracted wave shielding plate 6 becomes a second diffracted wave and becomes very small. Note that Fig. 3 a and b show an open square antenna with an L-shaped radio wave shield in cross section, and Fig. 3 c
shows a Sekiguchi antenna equipped with a radio wave shield with a straight cross-sectional shape.

FIG. 4 shows the propagation of the incident wave 7 and the diffracted wave 8 around the open circle area.

In FIG. 4a, an incident wave 7a that propagates from the primary radiator 5 to the edge 4a is diffracted at the edge 4a, becomes a diffracted wave 8a, and propagates to the side and rear of the antenna. The electric field pressure d of the diffracted wave 8a is expressed by the following equation using the electric field pressure i of the incident wave 7a and the diffraction coefficient Da. Pressure d=Da・Pressure i Da<<1 [21th 4th
In FIG. b, an incident wave 7a entering the edge 4a from the primary radiator 5 is diffracted at the edge 4a.

A part of this diffracted wave 8a becomes an incident wave 7b at the edge 4b, is diffracted from the green 4b, and propagates to the sides and rear of the antenna. Therefore, the electric field pressure d of the diffracted wave 8b from the edge 4b
d is the second diffracted wave 8b with respect to the incident wave 7a from the primary radiator 5, and is expressed by the following equation. Pressure dd=D
b・Pressure d=Da・Db・Pressure i [3} However, Db
indicates the diffraction coefficient at the edge 4b, where Db<<1.

As shown in FIG. 4c, by providing two diffracted wave shielding plates 6, the diffracted waves 8b propagating to the sides and rear of the antenna become the third diffracted waves, and the electric field of the diffracted waves can be made smaller. can.

Therefore, one or more diffracted wave shielding plates 6 are provided only in the area around the opening that is not directly hit by the radio waves emitted from the -order radiator 5, and the green 4b of the diffracted wave shielding plate and the edge 4a of the Sekiguchi By configuring the line connecting the phase center of the primary radiator to be convex with respect to the traveling direction of the radio waves reflected from the reflector, the radio waves propagating to the sides and rear of the antenna are directed to the primary radiator. The diffracted wave 8b is generated twice or more with respect to the incident wave 7a from the diffraction wave 5, and can be made sufficiently small. Although the above description has been made for the case of a parabolic antenna, the present invention is not limited to this, and the same effect can be obtained even when used around the closed end of the sub-reflector or main reflector of a Cassegrain antenna, as shown in FIG. .

As described above, in the antenna device according to the present invention, the radio waves propagating to the sides and rear of the antenna are This has the advantage of being able to reduce the front-to-side radiation ratio and improving the front-to-side radiation ratio and the front-to-back radiation ratio.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a reflector equipped with a conventional radio wave shielding plate, Fig. 2 is a diagram illustrating the effect when a conventional radio wave shielding plate is attached, and Fig. 3 is an illustration of an embodiment of the device of the present invention. A side view, FIG. 4 is an enlarged view of the portion around the closure in FIGS. 2 and 3, and FIG. 5 is a side view when the device of the present invention is used in a Cassegrain antenna. In the figure, 1 is a reflector, 2 is a radio wave shielding plate, 3 is a metal fin,
4 is green, 5 is a primary radiator, 6 is a diffracted wave shielding plate, 7 is an incident wave, and 8 is a diffracted wave. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 In an aperture antenna consisting of a primary radiator and a reflector, the radio waves radiated from the primary radiator are directly transmitted around the aperture of the reflector or outside the periphery of the radio wave shielding plate provided around the reflector. An antenna device characterized in that one or a combination of radio wave shields having a straight or L-shaped cross section are provided only in areas where the radio waves do not hit.