JP2711310B2 - Parabolic antenna device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a circularly polarized parabolic antenna device used for microwave communication such as reception of satellite broadcasting.

(Summary of the Invention) The present invention relates to a circularly polarized parabolic antenna device used for microwave communication such as reception of satellite broadcasting, and a reflector in front of a backfire helical antenna used as a primary radiator near the tip. Is provided.

(Prior Art) Conventionally, as this type of SHF circularly polarized parabolic antenna apparatus, there has been an apparatus using an endfire helical antenna as a primary radiator as shown in Japanese Patent Application Laid-Open No. 56-93402. This parabolic antenna apparatus has a problem that the loss of the primary radiator is large, and there is a problem of supporting strength of the primary radiator, etc., and as a solution to these problems, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 62-32707. Then, a proposal using a backfire helical antenna as a primary radiator is proposed.

FIG. 6 shows a conventional example of a parabolic antenna device using a backfire helical antenna as a primary radiator. In this figure, a backfire helical antenna 2 is disposed at the focal point of a parabolic reflector 1, and a coaxial line (for example, a semi-rigid cable or a rigid cable) 3 is provided at a feed point on the reflector side of the backfire helical antenna 2. Is connected. A cylindrical stay 4 made of resin or the like is provided around the coaxial line 3, and the base of the stay 4 is fixed to the reflecting mirror 1 by screwing or the like. The stay 4 covers and protects the coaxial line 3 and mechanically reinforces it to prevent the coaxial line 3 from bending, vibrating, and the like. The backfire helical antenna 2 is surrounded by a fidome 5 formed of a resin having a property of transmitting radio waves, and the fidome 5 is bonded and fixed to the cylindrical stay 4. The fidome 5 is a backfire helical antenna 2
Prevents water droplets due to rainfall from adhering to the surface and changing the characteristics.

Here, the backfire helical antenna 2 is
As shown in FIG. 7, it is composed of a matching disk 7 connected to the outer conductor 3A of the coaxial line 3 and one spiral conductor 8 connected to the center conductor 3B.

In principle, the current flowing on the line of the helical antenna proceeds smoothly on the helix of the helical antenna. Normally, the circumference of a spiral {that is, when the entire spiral is regarded as a cylinder, the circumference of the cylinder (hereinafter, referred to as a spiral circumference)}.
Electromagnetic waves are radiated from the tip of the helical antenna due to the presence of a larger reflector at the feeding point (end-fire helical antenna), but the circumference of the reflector at the feeding point is slightly larger than the circumference of the spiral. From the larger dimension to the same size, as it gradually decreases, the rear (feeding point side)
Electromagnetic waves are radiated to That is, a back lobe occurs. The backfire helical antenna selects each size in the way of actively using this backlobe. Here, the reflection plate is referred to as a matching disk.

In addition, as a backfire helical antenna,
As shown in FIG. 8, the spiral conductor 8 may have a flare shape 8A in which the cylindrical tip portion gradually widens,
As shown in FIG. 9, a spiral conductor 8 having a tapered shape 8B in which a cylindrical rear end (feeding point side) is gradually narrowed may be used. Further, as shown in FIG. 10, it is also possible to adopt a conical type having no flare portion and a flare shape 8A as a whole. 8 to 10, the connection of the matching disk 7 and the coaxial line 3 is the same as in FIG.

As is clear from the above explanation,
The main lobe MB of the helical antenna 2 is on the feed point side as shown in FIG.

(Problems to be Solved by the Invention) By using a backfire helical antenna as the primary radiator, the aperture efficiency of the parabolic antenna device is 68.
% Has reached a high rate.

FIG. 11 shows the radiation characteristics of this backfire helical antenna, where the front-to-back ratio is 14 dB. If the front-to-back ratio can be improved, the characteristics of the parabolic antenna device can be further improved.

An object of the present invention is to provide a parabolic antenna device capable of improving a front-to-back ratio of a primary radiator and thereby improving characteristics by adding a reflector to a backfire helical antenna used as a primary radiator. With the goal.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a backfire and a single-wire type cylindrical shape or a tapered or flared shape at the cylindrical end on the side where the focal point of the reflecting mirror exists.
The helical antenna is arranged such that the feeding point is on the side of the reflector, and a reflector fixed to a fidome surrounding the backfire helical antenna is arranged in front of the vicinity of the tip of the backfire helical antenna. .

The reflector may have a cylindrical shape with a bottom or a polygonal tube with a bottom, or may have a disk shape or a polygonal plate shape.

The reflector may have an outer diameter that is one to three times the outer diameter of the backfire helical antenna.

(Operation) The backfire helical antenna used in the present invention has directivity on the feed point side (rear end direction), that is, the main lobe faces the feed point side. However, since the front lobe exists at a relatively low level on the space side (toward the tip), the effect of collecting radio waves collected from the reflector to the primary radiator is somewhat reduced. Therefore, if a reflector is arranged on the space side (tip side) of the primary radiator, that is, the backfire helical antenna, using a fidome surrounding the backfire helical antenna,
Since radiation in the space direction is blocked, the front lobe level can be reduced, and the characteristics of the parabolic antenna device can be improved. In addition,
The fidome can be used for fixedly supporting the reflector, and the structure is not complicated.

(Example) Hereinafter, an example of a parabolic antenna device according to the present invention will be described with reference to the drawings.

In FIG. 1, a backfire helical antenna 2 is disposed at the focal point of a parabolic reflector 1, and is reflected forward (space side) by a predetermined distance (about several mm) from the tip of the backfire helical antenna 2. The body 10 is located. That is, in this embodiment, the reflector 10 is a bottomed cylindrical member made of a conductor such as a processed copper plate as shown in the sectional view of FIG.
Is adhered to the outside of the tip end surface (end surface on the space side) of the fidome 5 surrounding the. The fidome 5 is formed of a resin such as Teflon resin having a property of transmitting radio waves.

As shown in FIG. 2, the dimension d of the bottomed cylindrical reflector 10 is the outer diameter of the bottom surface 11, the dimension 1 is the length of the side surface 12, and the angle θ.
Is the angle formed by the extended surface of the bottom surface 11 and the side surface 12. Specifically, the angle θ can take any value of 90 ° or less,
May be tapered. On the other hand, if the dimension l is too long, it will affect the current flowing through the spiral conductor of the backfire helical antenna 2, so that the dimension l is made smaller than the dimension d. Further, as a result of experiments, it has been found that the reflector is also effective as a disk-shaped reflector having a dimension 1 = 0, that is, an outer diameter d.

The other configuration is the same as that of the conventional example shown in FIG.

Next, the operation of the above embodiment will be described. It is well known as the “reciprocity theorem” that the operation of the antenna in the case of reception is exactly the same as that in the case of transmission. Radio waves radiated from the backfire helical antenna 2 in FIG. 1 to the feeding point side are reflected by the parabolic reflector 1 and radiated in one direction of space. At this time, since the backfire helical antenna 2 has the main lobe MB on the feed point side, radio waves are efficiently radiated from the backfire helical antenna 2, but are also radiated in a somewhat spatial direction (tip direction). You. Radio waves directed in the space direction are parabolic reflectors 1
Although the radio wave is not concentrated in one direction but scattered over a wide angle range as in the case of the radio wave reflected by the reflector, the efficiency of the parabolic antenna apparatus is reduced, but the radio wave radiation in the spatial direction is blocked by the reflector 10. As a result, the front-to-back ratio of the backfire helical antenna 2 is increased, and the characteristics of the parabolic antenna device are improved.

 Next, the measurement results of this example will be described.

FIG. 3 shows the radiation characteristics of a backfire helical antenna as a primary radiator to which a reflector 10 is added. The front-to-back ratio is 19 dB, and the front-to-back ratio in the case of the conventional example in FIG. 11 is 14 dB. It can be seen that it is improved by 5dB compared to. However, the reflector 10 used for the measurement was cylindrical with a bottom, and the dimension d in FIG. 2 was 18 mm, 1 was 8 mm, and θ = 90 °.

FIG. 4 is a characteristic diagram comparing the gain of the parabolic antenna device according to the present invention with the gain of the conventional parabolic antenna device of FIG. In the drawing, the horizontal axis is (d / D) (where d is the outer diameter of the bottom surface of the reflector 10 in FIG. 2 and l = 0. D is the outer diameter of the cylindrical shape of the spiral conductor in FIG. 7). The vertical axis is the gain difference (dB). When the dimension l in FIG. 2 is 0, that is, when the reflector 10 has a disk shape with an outer diameter d, the gain of the parabolic antenna apparatus of the present invention is as follows. It can be seen that the gain is improved by 0.03 dB to 0.2 dB over the gain.

The gain of the conventional parabolic antenna device used for the measurement is 34.1 dB, and the gain of the parabolic antenna device of the present invention is 34.3 dB when d = 16 mm and D = 8 mm. The measurement sample of the parabolic antenna device of the present invention was the same as the measurement sample of the conventional parabolic antenna device used for comparison, except for the reflector.

In the embodiment of the present invention shown in FIG. 1, the case where the reflector 10 such as a processed copper plate is bonded to the fidome 5 is exemplified.
As shown in another embodiment of the present invention in FIG.
The reflective conductive film 20 of copper or the like can be formed by plating, vapor deposition, etching, or the like on the inside of the front end surface on the space side, which is easy in mass production.

In addition, in the description of FIG. 2 showing the reflector 10, the case where the reflector 10 has a cylindrical shape with a bottom or a disk shape is described. Alternatively, the shape may be a polygonal plate.

Further, in FIG. 5, the reflective conductive film 20 is fixed to the inner surface of the fidome 5, but the reflective conductive film 20 may be provided outside the front end surface of the fidome.

(Effects of the Invention) As described above, according to the parabolic antenna apparatus of the present invention, a reflector is disposed in front of the vicinity of the tip of a backfire helical antenna as a primary radiator, and the reflector is arranged in a spatial direction ( Since the addition of the primary radiator can be suppressed, the front-to-back ratio of the primary radiator is improved, and the characteristics of the parabolic antenna device can be improved. In addition, the reflector surrounds the backfire helical antenna. The effect is very large because it is simply fixed to the fidome and the structure is simple and suitable for mass production.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of a parabolic antenna device according to the present invention, FIG. 2 is a side sectional view of a reflector used in the embodiment, and FIG. 3 is radiation of a primary radiator in the embodiment. FIG. 4 is a graph showing a gain difference between the parabolic antenna device of the present invention and a conventional parabolic antenna device. FIG. 5 is a side sectional view showing a main part of another embodiment of the present invention. 6
FIG. 7 is a side sectional view showing a conventional example of a parabolic antenna device, FIG. 7 is a side sectional view of a specific example of a backfire helical antenna, and FIGS. 8 to 10 show modified examples of the backfire helical antenna. FIG. 11 is a side sectional view, and FIG. 11 is a radiation pattern diagram of a conventional primary radiator. 1 parabolic reflector, 2 backfire helical antenna, 3 coaxial line, 5 fidom, 7
... matching disk, 8 ... helical conductor, 10 ... reflector, 20 ...
Reflective conductive film.

Continuation of the front page (56) References JP-A-63-194403 (JP, A) JP-A-62-194707 (JP, A) JP-A-60-210012 (JP, A) JP-A-61-129903 (JP) , A)

Claims (4)

(57) [Claims] 1. A backfire / helical antenna having a single-line cylindrical shape or a tapered or flared end at a cylindrical end is disposed on a side where a focal point of a reflecting mirror exists, such that a feeding point is on the reflecting mirror side, A parabolic antenna device, wherein a reflector fixed to a fidome surrounding the backfire helical antenna is disposed in front of the vicinity of the tip of the backfire helical antenna. 2. The parabolic antenna device according to claim 1, wherein said reflector has a bottomed cylindrical shape or a bottomed polygonal cylindrical shape. 3. The parabolic antenna device according to claim 1, wherein said reflector has a disk shape or a polygonal plate shape. 4. The parabolic antenna apparatus according to claim 1, wherein an outer diameter of the reflector is one to three times an outer diameter of the backfire helical antenna.