JPH024164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spiral antenna with a good axial ratio.

Note that, for convenience of explanation, the spiral antenna is assumed to be a two-wire circular spiral antenna, and a case where a planar spiral antenna is used will be described here.

First, a conventional spiral antenna will be explained.

FIG. 1 is a block diagram of a conventional two-wire circular spiral antenna. In FIG. 1, 1 and 2 are power feeding points. When feeding points 1 and 2 are excited in opposite phases, currents 3a, 3b, and 3 are generated at points A, B, C, and D, respectively.
c, 3d flows. Furthermore, currents 3e, 3f, 3g, and 3h flow at points E, F, G, and H, respectively.
Here, the length along the arc between points A and C is a half wavelength, and similarly, the length along the arc between points B and D, between points E and G, and between points F and H is also a half wavelength. It is. Now, when vertically polarized wave 4 is incident, points A, B, C,
It is received at points E, F, G, and H when the horizontally polarized wave 5 is incident. Points A, B,
Consider a plane including C and D and perpendicular to the plane of the paper, and consider a case where vertically polarized waves 4 and horizontally polarized waves 5 are incident from various directions within that plane. When the angle θ from the direction perpendicular to the plane of FIG. 1 becomes greater than 0°, the reception levels of the vertically polarized waves 4 and the horizontally polarized waves 5 are different. This means that
This will be explained from the theory of array antennas assuming that there is a current distribution at points A, B, C, D, E, F, G, and H as shown in FIG. That is, points A, B, C,
The beamwidth of the radiation pattern due to the wave source at D is the point E, F, G, H due to the array factor.
is smaller than the beamwidth of the radiation pattern caused by the wave source. Therefore, the axial ratio is also poor when transmitting and receiving circularly polarized waves.

This invention was made to eliminate this drawback, and will be explained below by showing examples.

FIG. 2 is a diagram showing an embodiment of the invention. In FIG. 2, 1, 2, 4, and 5 are the same as those in FIG. In the case of Fig. 2, between points A and C, point B,
It is assumed that the lengths along the curves between D, between points E and G, and between points F and H are half a wavelength. The straight line distances between points A and C and between points B and D in the case of Figure 2 are smaller than the straight line distances in the case of Figure 1, so the points A,
When considering a plane including B, C, and D and perpendicular to the plane of the paper, the beam width of the radiation pattern from the wave sources at points A, B, C, and D is larger than the beam width in the case of FIG.

This means that the length of the intersection line between the plane containing horizontal polarization 5 and points A, B, C, and D and the spiral antenna is the same as the length of the intersection line between the plane containing vertical polarization 4 and points E, F, G, and H and the spiral antenna. By making the length shorter than the length of the intersection line, the influence of the array actor due to the presence of wave sources at points A, B, C, and D is reduced. By appropriately selecting the linear distances between points A and C and between points B and D, the beam widths for vertically polarized waves 4 and horizontally polarized waves 5 can be made equal.

Although the so-called gourd shape has been described above, modifications such as an ellipse or a rectangle may be considered depending on the purpose.

As described above, according to the present invention, the axial ratio can be improved by making the lengths of the lines of intersection of the spiral antenna and two mutually orthogonal planes containing two mutually orthogonal linearly polarized waves different. The effect is extremely large when this is used as a broadband antenna.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional two-wire circular spiral antenna, and FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, 1 and 2 are feeding points, 3a to 3h are currents, 4 is vertical polarization, and 5 is horizontal polarization. In addition,
In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] 1. A spiral antenna that receives two mutually orthogonal linearly polarized waves, characterized in that the lengths of the lines of intersection between the two mutually orthogonal planes containing the linearly polarized waves and the spiral antenna are different. spiral antenna.