JPS60176305A - Short back fire antenna for circularly polarized wave - Google Patents

Abstract

PURPOSE:To obtain a circularly polarized wave use antenna of a high gain and a small size, which scarcely causes fading, by providing a recessed part on the center part of a main passive reflector, and also adding a rotary mechanism part and a various phase shifter to a cross dipole feeding element. CONSTITUTION:A main passive reflector 4 is constituted of a metallic rim of the same cylindrical type, and a step-shaped circular recessed part 8 is formed on its center part in order to improve an antenna gain. As for a depth hs of the step, hs=-0.2lambda+AD1 (where 0.12<A<0.18) is desirable. On the other hand, this antenna is provided with a rotary mechanism 10 on a cross dipole 3 supporting part on the main passive reflector 4, as a countermeasure for fading, so that an attitude of said dipole element 3 is stabilized, and also a shape of a polarized wave can be corrected by a variable phase shifter 9. According to said constitution, the desired purpose can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement of a Noyot backfire antenna, and in particular to a circularly polarized wave antenna that is effective when applied to mobile communications such as maritime satellite communications by small ships. Regarding Yotobank Fire Antenna.

(Prior art) Figure 1 shows a conventional example of a circularly polarized bank fire antenna.
Shown below. FIG. 1(a) is a front perspective view, and FIG. 1(b) is a back view. This antenna, as shown in Figure 1(a),
It mainly consists of two large and small circular reflecting plates 1 and 2, a cross dipole feeding element 3, and a cylindrical metal rim 4.
It is characterized by having sharp directivity in the direction of the antenna axis due to multiple reflections of radio waves between the two reflectors 1 and 20. The open efficiency of this antenna is usually 80 to 85.
It has very high performance and has the potential for miniaturization, so it is expected to be used as an antenna for mobile communications, for example. Note that the signals from both dipole elements of the cross dipole feeding element 30 are rotated around 11 to obtain circular polarization characteristics.
1 cable 5, is synthesized by a 90° hybrid 6, and sent to a receiver (not shown) by a pongee cable 7.
do.

Inmarusanoto (
Since around 1990, the International Maritime Satellite Communications Organization (International Maritime Satellite Communication Organization) has
There are plans to launch a service called the Standard B system for ships of around 100,000 tons. In such a service, it is desirable to be as small and lightweight as possible due to issues such as installation space, and fading due to reflected waves from the sea surface, which reflects radio waves well, is unavoidable, so countermeasures are also required. Needs to be a woman.

Although the above-mentioned short back fire antenna is a promising antenna device that satisfies these requirements, the conventional antenna cannot be immediately adopted due to its size and fading countermeasures.

(Objects and Features of the Invention) The present invention improves the prior art and provides a Nyotobanok fire antenna for elliptical polarization, which is small, has a relatively high gain, and takes countermeasures against fading into consideration. purpose.

The features of the present invention are that high gain is achieved by providing a circular cedar in the center of the main reflector, and that the cross-dipole feeding element can be controlled to always maintain a predetermined relationship with the horizontal line. The reason is that

(Structure and operation of the invention) The present invention will be described in detail below using the drawings.

FIG. 2 shows an embodiment of the present invention, in which (a)+! A front view, and (b) a back view. In the figure, a step-shaped circular recess with a diameter D2 and a depth h8 is provided concentrically in the main reflecting plate 1 with a diameter of 8&round; It is a phase shifter. 10 is the attitude of the cross dipole feeding element 3 at the center of the main reflector 1! 1] A rotating mechanism including a motor 13 and an angle detector 12 for control, and other symbols are the same as in FIG.

First, we will talk about improving the radiation characteristics.Generally speaking, the radiation of a 7-way bass antenna is radiated from the cross-dipole feed element 3, as shown in FIG.
It consists of an electric field component that is multiple-reflected and radiated between the two reflectors 1 and 2', as shown by the solid line, and an electric field component that is reflected and radiated from the main reflector 1, as shown by the broken line. The radiation field of a short back fire antenna is mainly composed of the former, and its radiation characteristics are characterized by this component. On the other hand, although the latter component is quantitatively small, since there is a phase difference between it and the former component, it is thought that it degrades the characteristics when only the former component is considered. Therefore, if the phase difference between the two can be eliminated by some means, the radiation characteristics of the antenna can be improved and the gain can be increased.

The stepped circular portions 8 in FIG. 2 perform this phase difference control. This phase control amount is the diameter 1 of the main reflector 1, the diameter d of the sub-reflector 2, the depth hs and diameter D2 of the stepped circular recess 8, the height hr of the rim 4, the main reflector 1 of the sub-reflector 2
It is determined mainly by the height ha from the four parts 8
This depends on the depth hs of the main reflecting plates 1 and 2) and the ratio of the diameter D1 of the main reflecting plates 1 and 2 to the diameter D2 of the recess 8.

In Figure 4, the frequency used is 1. ．． 5 GH2 (λ=20Cr
n), D+”1.7λ, D2=0.7λ, 'hr=0
．． 257λ, d = '0.488λ.

Assuming ha=0.667λ, h8 is 0-0-2O! Antenna gain for omnidirectional antenna when changed by (
dB+) and axial ratio (dB). h8
-ON is equivalent to the typical /iodine backfire antenna of FIG. Compared to the gain at this time, when h8 is made deeper, the gain is improved within a certain range.

Regarding antenna gain, an improvement of 0.5 dB or more is generally evaluated as extremely large. In the example of FIG. 4, this range is the range where h8 is 4 to 14 and is 002
It corresponds to ~0.07λ.

The following is an experimental study of each of the above parameters. As the diameter d of the sub-reflector 2 increases, the beam width becomes narrower, but unnecessary side lobes are generated, so a range of 045 to 055λ is preferable. The diameter D1 of the main reflector 1 is limited to a range of 15 to 22λ in order to maintain high efficiency (aperture efficiency of 80 to 85%) as a New York fire antenna. Diameter D2 of four parts 8
is a function of the diameter D1 of the main reflector 1, and is preferably in the range of 04 to 0.7 Dt in order to narrow the beam width without generating side lobes. The depth hs (cm) of the recess 8 also depends on the diameter D+(crn) and wavelength (α) of the main reflector 1, and in order to obtain the gain improvement of 0.5 dB or more, it must be within the range shown by the following formula. Must be set.

hg==-0, 2λ+AD,...(1) However, 0
．． 12 < A <0.1'8 In addition, the height h of the rim 4
r is approximately 0.252, and the avidity ha of the sub-reflector 2 is 05 to 0.
Generally, the range d is set to 68λ.

Next, we will discuss countermeasures against fading. In Japanese Patent Application No. 56-44100, the waves reflected from the sea surface of radio waves from satellites in maritime satellite communication have the property that the long sleeve of elliptically polarized waves is almost parallel to the sea surface, as shown by ■ in Figure 5. Focusing on this, the polarization characteristics of the ship's antenna are orthogonal to ■, as shown by ■ in the same figure (■ The axial ratio is the same)
It has been shown that reflected waves can be suppressed by making sure that the long axes are perpendicular to each other (1) that the polarized waves are in opposite directions of rotation.

As is clear from the figure, the polarization characteristics of the ship antenna indicated by ■ have the property that the long axis of the ellipse is almost perpendicular to the sea surface. Therefore, in order to realize the system of Japanese Patent Application No. 56-44100, it is necessary to ensure that the polarization characteristics of the ship's antenna always have the above characteristics regardless of the movement of the ship or the movement of the ship. . The polarization characteristics that are orthogonal to this sea surface reflection are obtained by rotating the two dipole elements by 45 degrees from the horizontal plane (or vertical +lIb) (i.e., one of the lines connecting the adjacent tips of the cross dipole is parallel to the horizontal plane). This can be achieved by controlling the phase amount of the variable phase shifter 9 inserted into one of the power feeding ports for the two orthogonal dipoles in this state. FIG. 6 shows the relationship between the phase amount of the variable phase shifter and the shape of polarization.

Generally, in an antenna attached to an Az-EA type mount, the surface of the antenna rotates due to the movement of the ship. Correspondingly, the cross dipole, which is the feeding element of the short backfire antenna, also rotates, making it impossible to obtain the desired polarization characteristics, and if this continues, the effect of the above-mentioned fading reduction method will be lost. The antenna according to the invention comprises:
The main reflector is rotated so that one of the lines connecting the adjacent tips of the cross dipole is always horizontal by giving the cross dipole the same amount of rotation in the opposite direction as the rotation angle of the cow antenna due to the movement of the ship. Rotation mechanism 10 is attached to the upper cross dipole support part.
"1" has been established. In FIG. 2, 3 is a motor that rotates the dipole, and 12 is its angle detector. This rotation angle β is controlled by an antenna control section (not shown).

Here, ψ is the relative azimuth angle of the satellite when there is no movement θ The relative elevation angle of the satellite when there is no movement δ: Roll angle of the ship γ゛ When the pitch angle of the ship is taken, the rotation angle β is determined by the following formula β = ca
s' (sinψSinψ′μsγ+ CO3ψ residenceψ
-4ψsinψ' sinδsinγ)°゛°゛(2
) and ψ′ is defined by the following equation.

...(3) FIG. 7 shows the configuration of the power feeding section of the antenna.

This antenna has features such as a step-shaped recess formed in the center of the main reflector, a variable phase shifter for reducing fading, and a dipole rotation function. . Further, in the figure, 11 is a matching circuit for the dipole antenna element.

(Effects of the Invention) As explained above, by adding a step structure concentrically on the main reflector, the gain of the Yacht Bassock fire antenna is improved, and the rotation mechanism of the cross dipole and the variable phase shifter are By adding , it is possible to have a polarization characteristic in which the long axis of the polarization ellipse is always perpendicular to the horizontal line. This antenna +a can be said to have a great effect as a mobile communication antenna, where it is desirable to have an antenna that is as small and lightweight as possible.

[Brief explanation of drawings]

Figures 1 (a) and (b) are a front perspective view and a back view of an example of a conventional circularly polarized Noyotobanok fire antenna;
3 is a schematic cross-sectional view for explaining the operation of the circularly polarized short back fire antenna according to the present invention, and FIG. 4 is a diagram showing the gain and axial ratio characteristics of the antenna according to the present invention. 5 and 6 are schematic diagrams for explaining the polarization characteristics of the antenna of the present invention, and FIG. 7 is a block diagram showing an example of the structure of the feeding section of the antenna of the present invention. 1.2...Reflector plate, 3...Cross dipole feeding element, 4...Cylindrical metal rim, 5,7.Coaxial cable,
6. 90° high print, 8. Stepped circular recess, 9. Variable phase shifter, 10. Rotation mechanism, 11. Matching circuit, 12. Angle detector, 13. Motor. Patent Applicant International Telegraph Co., Ltd. Representative Inuzuka 1 person outside the university Figure 2 Figure 3 Figure 4 15 Figure 5 Figure 6 (i l(N=O°) (ii) (s=30') =60') (iVl(,5=90')Figure 7

Claims (1)

[Claims] (I) Four stepped circular parts are formed in the center of the main reflector, and two dipole elements are arranged on the axis of the cross dipole at an angle of 45 degrees with respect to the water plane and the 5Ji plane. A rotation mechanism for circularly polarized wave is added to control the tilting, and a variable phase shifter for reducing fading is connected to one of the two dipole elements. Nokfire antenna. (2) The stepped circular recess has a wavelength of λ.
If the diameter of the main reflecting plate is -02λ+A
2. The Nyoto pack fire antenna for circularly polarized waves according to claim 1, characterized in that DI (here, 0.12<A<0.18).