JPH0533844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circularly polarized parabolic antenna device used for microwave communications such as receiving satellite broadcasting.

(Summary of the Invention) The present invention provides a circularly polarized parabolic antenna device used for microwave communications such as receiving satellite broadcasting, in which a primary radiator has a single-wire cylindrical shape or a tapered or flared shape at the end of the cylindrical shape. It uses a backfire helical antenna with

(Prior art) Conventionally, this type of SHF circularly polarized parabolic antenna device used an endfire helical antenna as a primary radiator, as shown in Japanese Patent Application Laid-open No. 93402/1983. . FIG. 4 shows an example of the configuration in this case. In this figure, an endfire helical antenna 2 is placed at the focal point of a parabolic reflector 1, and power is supplied to it via a coaxial line 3.

(Problems to be Solved by the Invention) By the way, in the above conventional configuration, the endfire helical antenna 2 is used as the primary radiator.
Since the feeding point is parabolic reflector 1
As a result, the coaxial line 3 is extended across the front surface of the parabolic reflector 1. Therefore, it is difficult to use the coaxial line 3 as a support member for supporting the endfire helical antenna 2, and in reality, the support structure for the endfire helical antenna 2 becomes complicated. Furthermore, since this type of antenna device is used outdoors, measures against rain are also required. Furthermore, the coaxial line 3 that crosses the reflecting mirror 1 causes blocking, and the longer coaxial line 3 increases the loss.

(Means for Solving the Problems) In view of the above points, the present invention uses a backfire helical antenna as a primary radiator, and connects a coaxial line protected by a stay to a backfire helical antenna.
By using it as a support structure for a helical antenna and further surrounding the backfire helical antenna with a radome, we aim to provide a highly practical parabolic antenna device that is simple in structure, waterproof, and highly sensitive. be.

In the present invention, at or near the focal point of the reflecting mirror,
A backfire helical antenna wound in a flared shape is arranged at the cylindrical end of the single wire type, and a coaxial line installed on the central axis of the reflector is connected to the backfire helical antenna. A parabolic antenna device, wherein a cylindrical stay is provided to cover and protect the antenna, the base of the cylindrical stay is fixed to the reflector, and the backfire helical antenna is surrounded by a radome that is watertightly joined to the cylindrical stay. It's hot,
The backfire helical ontenna consists of a matching disk connected to the outer conductor of the coaxial line and one spiral conductor connected to the center conductor, and the circumference of the spiral conductor (the entire spiral is considered as a cylinder). If S is the circumferential length of the cylinder, α is the pitch angle, β is the angle of the flare, c is the circumferential length of the matching disk, and λ is the wavelength of the electromagnetic wave, then 0.7λ≦S The above problems are solved by the following configuration: ≦1.1λ 6 degrees≦α≦20 degrees 0<β<45 degrees 0.7S≦c≦0.9S.

(Function) The backfire helical antenna used in the present invention has directivity toward the feeding point, that is, the main lobe faces toward the feeding point, so the end near the reflecting mirror can be used as the feeding point. . Therefore, when the backfire helical antenna is placed at the focal point of the reflector, the feed coaxial line is drawn out over the shortest distance on the center axis of the reflector. Therefore, the coaxial line can be protected by the stay and these can be used as a support structure for the backfire helical antenna, thereby simplifying the structure.
In addition, by covering the backfire helical antenna with a radome, it can be made waterproof and rain countermeasures can be easily implemented. moreover,
There is almost no blocking caused by the coaxial line, and power loss can be reduced, and together with the flare shape formed at the end of the backfire helical antenna to improve the front-to-back ratio of the radiation amount, high-sensitivity reception characteristics are achieved. can be realized.

(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 5 is placed at the focal point of a parabolic reflector 1,
A coaxial line (for example, a semi-rigid cable, a rigid cable, etc.) 6 is connected to a feeding point on the reflector side of this backup fire helical antenna 5. A cylindrical stay 11 made of resin or the like is provided around the coaxial line 6 as shown in FIG.
The base of is fixed to the reflecting mirror 1 with screws or the like. The stay 11 covers and protects the coaxial line 6 and mechanically reinforces it to prevent bending of the coaxial line 6.
Prevent vibration etc. The backfire helical antenna 5 is surrounded by a radome 13 made of a resin that transmits radio waves, and the radome 13 is watertightly bonded to the cylindrical stay 11. The radome 13 prevents water droplets from adhering to the backfire helical antenna 5 due to rain and changing its characteristics.

Here, FIG. 2A is a reference example showing the basic configuration of the backfire helical antenna 5, in which one matching disk 7 is connected to the outer conductor 6A of the coaxial line 6, and one is connected to the center conductor 6B. It consists of a spiral conductor 8. FIG. 2B shows a configuration according to this embodiment, which has a flared shape at the cylindrical end (non-power feeding side) of a single wire type. That is, a flare 8F is formed at the tip of the spiral conductor 8. Other details are the same as in Figure 2A. Further, FIG. 2C shows a single wire type with a tapered end at the cylindrical end (power feeding side). That is, a taper 8T is formed at the end of the spiral conductor 8 on the power supply side. Other details are the same as in Figure 2A.

In principle, the current flowing on the line of the helical antenna smoothly travels on the spiral of the helical antenna. Normally, the tip of the helical antenna is larger than the circumference of the helix (that is, if the entire helix is considered a cylinder, the circumference of the cylinder (hereinafter referred to as the helix circumference)), so the tip of the helical antenna is larger. Electromagnetic waves are emitted from the (endfire helical antenna), but as the circumference of the reflector starts out being slightly larger than the circumference of the spiral, it goes through the same size, and gradually becomes smaller, Electromagnetic waves will be radiated to the (power feeding end side). In other words, bats cloves are produced. The dimensions of the backfire helical antenna are selected with the idea of making active use of this backlobe. Here, the reflecting plate is referred to as a matching disk.

In Figure 2 A, B, and C, S is a spiral conductor 8
, a is the pitch angle of the spiral, and c is the matching disk 7.
β is the opening angle of the flare, 8T is the taper, and 8F is the flare.

Figures 5 to 8 show the helical circumference S of the backfire helical antenna and the front-to-back ratio of the radiation amount of the backfire helical antenna {log
(F/B)} (however, pitch angle α = 6, 10, 20 degrees, opening angle β of flare 8F portion = 0, 20 degrees, circumference length of matching disk c = 0.7S,
0.9S, λ is the wavelength of electromagnetic waves), S is 0.7λ to
It can be seen that a front-to-back ratio of several dB to more than 10 dB is obtained at 1.1λ.

Figures 9 to 12 show the relationship between the helical pitch angle α of the backfire helical antenna and the front-back ratio of the radiation amount of the backfire helical antenna (S = 0.7λ, 1λ, 1.1λ, β =
0, 20 degrees, c = 0.7S, 0.9S), α is 6 to
It can be seen that a front-to-back ratio of several dB to more than 10 dB is obtained at 20 degrees.

Figures 13 to 17 show the opening angle β of the flare 8F portion of the backfire helical antenna;
This is the relationship between the front and back ratio of the radiation amount of the backfire helical antenna (however, S = 0.7λ, 1λ,
1.1λ, α=6, 10, 20 degrees, c=0.7S, 0.9S), with flare 8F, 0<
When β < 45 degrees, a front-to-back ratio of several dB to more than 20 dB can be obtained, and by appropriately forming the flare 8F, the front-to-back ratio can be further improved than when β = 0 (meaning no flare). I understand that.

Figures 18 to 22 show the relationship between the circumference c of the matching disk of the backfire helical antenna and the front-back ratio of the radiation amount of the backfire helical antenna (S = 0.7λ, 1λ, 1.1λ ,α
= 6, 10, 20 degrees, β = 0, 20 degrees), c is
It can be seen that a front-to-back ratio of several dB to more than 10 dB is obtained at 0.7S to 0.9S.

Although the case of β = 45 degrees is not mentioned in the relationship between the helical circumference length S and the front-back ratio in FIGS. 5 to 8, the opening angle β of the flare 8F portion in FIGS. 13 to 17 is In relation to the front-to-back ratio, β = 0 degrees and β = 45 degrees are the same value, so they are omitted. For the same reason, β = 45 degrees in the relationship between the pitch angle α and the front-to-back ratio in Figures 9 to 12, and the relationship between the circumferential length c of the matching disk and the front-to-back ratio in Figures 18 to 22. Cases have been omitted.

From the above results, we use the backfire helical antenna 5 with flare 8F as shown in Figure 2 (b), 0.7λ≦S≦1.1λ 6 degrees≦α≦20 degrees 0<β<45 degrees 0.7S≦c≦0.9 By setting as shown in S, a backfire helical antenna with a good front-to-back ratio can be realized.

Note that it is necessary to match the coaxial line 6 and the helical conductor 8 in order to reduce reflection between the coaxial line 6 and the helical conductor 8 and to obtain good VSWR as an antenna. The matching can be achieved by appropriately adjusting the distance a between the matching disk 7 and the straight portion 9 of the spiral conductor facing the matching disk 7, or by adjusting the connecting portion between the spiral conductor 8 and the coaxial line 6 ( There are two methods: expanding the shape of the spiral conductor into a tapered shape (conical shape) from the feeding end of the backfire helical antenna and matching it with the circumference S of the corresponding spiral conductor. Of course, improvements can be made by combining these.

The most preferable arrangement of the backfire helical antenna 5 and the coaxial line 6 is when the direction of the helical axis of the backfire helical antenna 5 and the direction in which the coaxial line 6 is drawn out are located on the central axis of the reflector 1. The directivity of the backfire helical antenna 5 at this time, that is, the main lobe MB, is shown, for example, by the dotted line in FIG.

Next, the operation of the above embodiment will be explained in the case of reception. Electromagnetic waves incident in the direction of arrow W in FIG.
incident from the feeding point side. At this time, the backfire helical antenna 5 is connected to the main lobe MB.
The electromagnetic waves reflected by the reflector 1 are efficiently received by the backfire helical antenna 5. In this case, the backfire helical antenna 5 exhibits good characteristics when the received electromagnetic waves are circularly polarized waves, like a normal endfire helical antenna.

The parabolic antenna device shown in the above embodiment is
Since the backfire helical antenna 5 is used as the primary radiator used in combination with the reflector 1, the feed point can be set at the end close to the reflector 1, and the coaxial line 6 for power feed can be drawn out at the shortest distance. be able to. Therefore, by protecting and reinforcing the coaxial line 6 with the cylindrical stay 11,
It can be used as a support structure for the backfire helical antenna 5, and the structure can be simplified. Further, by covering the periphery of the backfire helical antenna 5 with the radome 13, waterproofness can be ensured. Furthermore, since the coaxial line 6 can be short, power loss can be reduced, and since the coaxial line 6 does not need to cross the front surface of the reflector 1 and no blocking occurs, a flared shape can be used at the end of the backfire helical antenna. In combination with the improved front-to-back ratio of the radiation amount, highly sensitive reception characteristics can be obtained. As described above, the separate antenna device shown in the embodiment has a simple structure, is suitable for mass production, and is advantageous in terms of miniaturization.

In addition, in the above embodiment, the stays 11, 11
If A is made of a radio wave absorber, side lobes caused by the coaxial line 6 can be suppressed.

(Effects of the Invention) As explained above, in the discrete antenna device of the present invention, a backfire helical antenna is arranged on the side where the focal point of the reflector is present, a coaxial line is connected to the backfire helical antenna, and a coaxial line is connected to the backfire helical antenna. Since the coaxial line is protected by a stay and the backfire/helical antenna is surrounded by a radome, the support and waterproofing of the backfire/helical antenna can be ensured with a simple structure. The effect is extremely large.

[Brief explanation of drawings]

Figure 1 is a side sectional view showing an embodiment of a parabolic antenna device according to the present invention, Figure 2 A is a side sectional view of a reference example which is the basic configuration of a backfire helical antenna, and Figure 2 B is used in the embodiment. 2C is a side sectional view showing a modification of the backfire helical antenna, FIG. 3 is an enlarged sectional view of FIG. 1, and FIG. 4 is a side sectional view of a conventional parabolic antenna device. The side sectional views, FIGS. 5 to 8 are graphs showing the relationship between the circumference S of the backfire helical antenna and the front-to-back ratio of the backfire helical antenna, and FIGS. 9 to 12 are graphs showing the pitch of the backfire helical antenna. Graphs showing the relationship between the angle α and the front-to-back ratio of the backfire helical antenna, and Figures 13 to 17 are graphs showing the relationship between the opening angle β of the flare portion of the backfire helical antenna and the front-to-back ratio of the backfire helical antenna. , FIGS. 18 to 22 are graphs showing the relationship between the circumferential length c of the matching disk and the front-to-back ratio of the backfire helical antenna. 1... Parabolic reflector, 5... Backfire helical antenna, 6... Coaxial line, 7...
Matching disk, 8... spiral conductor, 11... stay,
13...Radome.

Claims (1)

[Scope of Claims] 1. A backfire helical antenna having a single wire cylindrical end wound in a flare shape is disposed at or near the focal point of the reflecting mirror,
Connecting a coaxial line installed on the central axis of the reflecting mirror to the backfire helical antenna,
A cylindrical stay is provided to cover and protect the coaxial line, a base of the cylindrical stay is fixed to the reflector, and a parabola surrounds the backfire helical antenna with a radome that is watertightly joined to the cylindrical stay. In the antenna device, the backfire helical antenna includes a matching disk connected to the outer conductor of the coaxial line and one spiral conductor connected to the center conductor, and the circumference of the spiral conductor is The length (if the entire spiral is considered as a cylinder, the circumference of the cylinder) is S, the pitch angle is α, the flare angle is β, the circumference of the matching disk is c, and the wavelength of the electromagnetic wave is λ A parabolic antenna device characterized in that: 0.7λ≦S≦1.1λ 6 degrees≦α≦20 degrees 0<β<45 degrees 0.7S≦c≦0.9S. 2. The parabolic antenna device according to claim 1, wherein the cylindrical stay is made of a radio wave absorber.