JPH0213843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an offset parabolic antenna that is used in the microwave band or millimeter wave band and is composed of a reflecting mirror and a primary radiator.

This type of offset parabolic antenna is
As shown in the figure, it consists of a primary radiator 1 and a reflecting mirror 2 consisting of a parabolic mirror of revolution. In addition, Figure 1a
1b shows a view from the side, and FIG. 1b shows a view from the front.

For ease of explanation, we will set up an orthogonal coordinate system XYZ in which the focal point of the rotating parabolic mirror is the origin, the axis of rotation is the Z axis, and the Y axis is the direction perpendicular to the plane of symmetry in the structure of the offset parabolic antenna described above. . When a straight line extending radially from the focal point in a plane parallel to the aperture of the primary radiator 1 is projected onto the reflecting mirror 2, the shadow of the straight line seen from the Z-axis direction is shown by the dotted line in FIG. The result will be a curve like this.

Therefore, this offset parabolic antenna is
When the electric field is excited with a linearly polarized wave parallel to the X axis, as shown by the solid line in Figure 2a, the electric field is
When parallel to the axis, as shown by the solid line in Figure 2b, the direction of the electric field of the radio waves emitted from the primary radiator 1 and incident on the reflector 2 is bent by the reflector 2, resulting in cross polarization. It had the disadvantage of generating wave component 3. FIG. 5 shows the radiation pattern in the plane of symmetry (XZ plane) in the structure of this offset parabolic antenna. In the figure, the solid line is the radiation pattern of the main polarization component, and the dotted line is the radiation pattern of the cross-polarization component. Further, the phase of the electric field of the cross-polarized component is +90 degrees on one lobe side and -90 degrees on the other rope side with respect to the phase of the electric field in the main beam direction of the main polarized component. Furthermore, when this offset parabolic antenna is excited with circularly polarized waves, the direction of the electric field is bent by the reflecting mirror 2, so the direction of the main beam of the main polarization component is different from right-handed circularly polarized waves to left-handed circularly polarized waves. The drawback was that the waves differed due to circular polarization.

In order to eliminate such drawbacks, this invention
The primary radiator is excited with a main polarization component and a component consisting of a correction electric field orthogonal to the electric field of the main polarization component, and will be described in detail below with reference to the drawings.

FIG. 3 is a diagram explaining the principle of this invention, showing the direction of the electric field of the cross-polarized wave component 3 generated in the reflecting mirror 2 when excited with the main polarized wave component 4, and the direction of the electric field necessary to cancel the cross-polarized wave component 3. A correction electric field 5 is shown.

First, when the primary radiator is excited with the X polarization component 6 as the main polarization component 4, the direction of the electric field is bent by the reflecting mirror 2, producing a Y polarization component as the cross polarization component 3. The electric field after being reflected by the reflecting mirror 2 is divided into a main polarization component 4 and a cross polarization component 3 as shown in the column of electric field in the reflecting mirror in FIG.

Therefore, the primary radiator is excited by applying a correction electric field 5 in advance so as to cancel out this cross-polarization component 3, and each part of the primary radiator, which is divided into two halves with the plane of symmetry (XZ plane) as the boundary, is It is excited with a correction electric field 5 of the Y polarization component having a phase difference of 90 degrees and -90 degrees with respect to the polarization component 4, respectively. In this case, the reason why the main polarization component 4 has a phase difference of 90 degrees and -90 degrees is that the phase of the ropes on both sides of the Z axis of the radiation pattern due to the correction electric field 5 in the reflecting mirror 2 is
90 respectively for the phase of the main rope of the main polarization component.
By setting the angles to -90 degrees and -90 degrees, the originally existing main polarized wave component 4 can be in opposite phase to the radiation pattern of the cross polarized wave components generated by the reflector 2, so that Polarization components can be canceled out. By adopting such a configuration, the cross-polarized wave component 3 generated by the reflecting mirror can be canceled out by the component generated by the correction electric field 5 in the primary radiator, so that a good low-level cross-polarized wave component 3 can be obtained. A radiation pattern can be realized.

The above description has been made for the case where the main polarization component 4 is the X polarization component 6, but as shown in FIG. 3, the same effect can be obtained by using this invention even when only the Y polarization component 7 is present. Can be done. Furthermore, since it is possible to cancel out cross-polarized components when excited with X-polarized waves and Y-polarized waves, the main beam direction of the main polarized components of the radiation pattern when excited with circularly polarized waves can be changed to right-handed circularly polarized waves. can be matched with left-handed circular polarization.

As an example of a specific excitation method in the primary radiator 1, when the primary radiator 1 is used for transmission, the fourth
As shown in the figure, there is a method of extracting a part of the power of the main polarization component 4 using probes 8a and 8b and inputting that power as a correction electric field 5 through a transmission line 9 again using probes 8c and 8d. . Fourth
Figure a is an external view of the primary radiator 1 viewed diagonally from the front.
A part of the power of the main polarized wave component 4 extracted by step b is transmitted to probes 8c and 8d provided in the input surface 11 through a transmission line 9, and is inputted as a correction electric field 5. The distance between the output surface 10 and the input surface 11 and the length of the transmission line 9 are determined by the phase of the main polarized wave component propagating within the primary radiator 1 and the phase of the main polarized wave component that is extracted by the probes 8a and 8b and passed back through the transmission line 9 to the probe 8.
c and 8d are selected so that the phase of the radio waves input as the correction electric field has the predetermined phase difference shown above. Figure 4b is a diagram looking at the feed side from the opening of the primary radiation hazard 1, where the main polarization component 4 is the X polarization component 6.
This figure shows the output probe 8a, the input probe 8c, the transmission line 9, and the correction electric field 5 excited by the input probe 8c, which are related to the case of . Similarly, FIG. 4c is a diagram looking at the feed side from the aperture of the primary radiator 1, and shows the output probe 8b, which is related when the main polarization component 4 is the Y polarization component 7.
It shows the input probe 8d, the transmission line 9, and the correction electric field 5 excited by the input probe 8d.

As explained above, by applying the present invention to the primary radiator of an offset parabolic antenna,
When exciting with linear polarization, a radiation pattern with a low level of cross-polarized components can be achieved, and when exciting with circular polarization, the main beam direction of the main polarization component can be changed between right-handed circular polarization and left-handed circular polarization. It can be matched with circular polarization.

[Brief explanation of drawings]

Figure 1 is a block diagram of an offset parabolic antenna, Figure 2 is a diagram explaining changes in the direction of the electric field, Figure 3 is a diagram explaining the principle of this invention, and Figure 4 is a diagram of a primary radiator according to this invention. The configuration diagram, FIG. 5, is a diagram showing the radiation pattern of a conventional offset parabolic antenna. In the figure, 1 is the primary radiator, 2 is the reflector, 3 is the cross polarization component, 4 is the main polarization component, 5 is the correction electric field, 6 is the X polarization component, 7 is the Y polarization component, and 8 is the probe. , 9 is a transmission line, 10 is an output surface, and 11 is an input surface. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1 Used in microwave or millimeter wave bands,
In an offset parabolic antenna consisting of a reflector and a primary radiator, when the offset parabolic antenna is excited with linearly polarized waves, the primary radiator is connected to the main polarization component, the electric field of this main polarization component, and the space. The temporal phase of the correction electric field in each part bisecting the primary radiator with the plane of symmetry in the structure of the offset parabolic antenna as the boundary is the main polarization. One side is +90 relative to the phase of the electric field of the wave component.
An offset parabolic antenna characterized in that one side is at -90 degrees and the other side is at -90 degrees.