JPH0720010B2 - Circular polarization modified beam antenna - Google Patents

Description

TECHNICAL FIELD The present invention relates to an antenna that forms a circularly polarized modified beam.

(Prior Art) In a radar that searches for targets on the ground, at sea, or in the air, the horizontal beam is narrowed in order to increase the azimuth resolution,
The vertical beam may have a cosec-square characteristic in order to keep the reception level from the target constant with respect to the distance.

In addition, the above radar may use circularly polarized waves to reduce reflected waves from rainfall. In such a case, in order to effectively reduce the reflected wave from rainfall, it is necessary to maintain the circular polarization characteristic over a relatively wide range of angles covered by the modified beam.

Documents describing conventional circular polarized wave modified beam antennas include: (1) Mizusawa, et al. “Double curved double reflector antenna for circular polarization”, IEICE, Space Navigation Electronics Research Group, Material No. A.P74 -81, PP25-32 (2) Xie, et al. "Design and radiation characteristics of H-plane fan-type cosecant beam horn antenna with dielectric insertion", IEICE Transactions, '82 / 10 vol.J-65B, No. There are 10, PP1221-1228.

FIG. 5 is a diagram for explaining an example of the configuration of the antenna described in the above literature (1). FIG. 5 (a) is a diagram showing an example of a conventional circular polarized wave modified beam antenna.
An antenna composed of a next horn 1 and a reflecting mirror 2 in which the upper part of the reflecting mirror is modified to form a modified beam (COSEC squared characteristic), and L1, L2, and L3 indicate the traveling directions of radio waves,
C1 and C2 indicate the directivities of the primary horn 1 for horizontal polarization and vertical polarization, respectively.

Since the primary horn 1 is a rectangular aperture horn, the aperture distributions for horizontal and vertical polarized waves are different, and the directivities for both polarized waves are also different. Therefore, even if a circularly polarized wave is obtained in a specific angular direction (for example, horizontal direction) in the deformed beam,
In other angle directions, the mutual amplitude relationship of both polarized waves becomes different, and circular polarized waves cannot be obtained.

FIG. 5 (b) is a modification of the above antenna, and is a diagram showing an antenna similar to the antenna described in the above document (1). This antenna is composed of a primary horn 3, a sub-reflection mirror 4 and a main reflection mirror 5, and L4, L5, and L6 indicate the traveling directions of radio waves. With this antenna, a conical horn is used as the primary horn, and the main and sub two reflecting mirrors are constructed with special curved surfaces to obtain circular polarization characteristics within the predetermined angle range of the modified beam. In order to form a deformed beam in such an antenna, a special curved surface is used for the main and sub-reflecting mirrors, which requires a high degree of special technology for design and manufacture. It is difficult to obtain directivity, and the production cost is high.

FIG. 6 is a diagram showing an example of the modified beam antenna described in the above-mentioned document (2), in which a dielectric 8 is inserted into a fan-shaped horn 7 and an opening surface is made into a special curved surface in order to obtain a modified beam. It is the one. Even if radio waves of two polarizations, horizontal and vertical, are applied to this antenna, the propagation attitudes of both polarizations in the fan-shaped horn 7 are different, so the distributions of both polarizations on the aperture plane are different, and similarly, the deformation beam Circularly polarized waves cannot be obtained within a predetermined angle range.

(Problems to be Solved by the Invention) As described above, the conventional antenna cannot obtain circular polarization within the predetermined angle range within the modified beam, or obtains circular polarization within the predetermined angle range. However, there are problems such as difficulty in designing and manufacturing and cost.

(Means for Solving the Problems) The object of the present invention is to eliminate the above-mentioned drawbacks of the conventional antenna, to obtain a circularly polarized wave within a predetermined angle range within the modified beam, and to design and manufacture the circularly polarized wave easily. It is to realize a polarization modified beam antenna.

The configuration of the antenna to which the present invention is applied is such that a circularly polarized wave generating device made of a parallel metal plate grating is provided in the vicinity of the opening surface of the cheese antenna that generates a plane wave, and the front surface thereof has a thickness in the direction orthogonal to the opening surface. A circular polarized wave modified beam antenna characterized in that the dielectric material having a constant thickness is provided in the horizontal direction, which changes along the in-plane vertical direction. A thickness direction X axis from the lower end of the grid, which is horizontal and has a rear end of the dielectric member that is orthogonal to the opening face as zero, and a direction in which the rear lower end of the dielectric member has zero and extends vertically upward along the opening face. Is the Y axis, the refractive index is n, the radio wave tilt angle is θ, and the X coordinate value of the point where the output surface of the dielectric intersects the X axis is x1, the change in the thickness of the dielectric in the X axis direction. On the XY plane, Which is a circularly polarized wave modified beam antenna extending uniformly in the horizontal direction along the opening surface.

(Embodiment) FIG. 1 is a view showing an embodiment of the present invention, which is an example in which the present invention is applied to a so-called cheese antenna. The same figure (a)
Is a perspective view showing the appearance, FIG. 2B is a cross-sectional top view, FIG. 1C is a cross-sectional view taken along line AA in FIG. 1A, and FIG. Reference numeral 10 in FIG. 1 denotes a reflecting mirror portion, which is surrounded by the upper flat plate 10a, the lower flat plate 10b, and the parabolic cylindrical reflecting surface 10c. Reference numeral 11 is a primary horn for supplying electric waves to the reflecting mirror section 10, which is a so-called HogHorn type having a parabolic cylindrical reflection surface inside the horn, and its opening has a parabolic cylindrical shape. It is placed near the focal point (not shown) of the reflecting surface 10c and serves as a line source for the reflecting surface 10c. In the figure, L10 is the primary horn 11
It shows the traveling direction of the radio wave inside.

Reference numeral 12 in FIG. 1 (d) is a circularly polarized wave generator, the structure of which is shown in FIG. FIG. 4 (a) is a top sectional view and FIG. 4 (b) is a front view. This circularly polarized wave generator 12 has a conductor structure in which a foamed dielectric material 20 is filled with a parallel metal plate grating 21 with respect to the upper plane plate 10a or the lower plane plate 10b at an inclination of 45 degrees. In addition, L20 in FIG. 4 (a) indicates the direction of the incident electric wave.

In FIG. 1, 13 is a dielectric, and the thickness in the direction orthogonal to the opening surface 14 changes according to the upward direction shown in FIG. 1, and has a constant thickness in the direction orthogonal to the paper surface in FIG. Figure 1 (d)
L11, L12, L13, and L14 indicate the traveling directions of radio waves after refraction by the dielectric 13.

FIG. 2 is a view for explaining the action of the dielectric 13 and shows the cross section and the coordinate system of the dielectric 13 on the same plane as the cross section of FIG. 1 (d). X and Y represent coordinates in the cross section, the origin of the XY coordinates is provided at the lower corner of the dielectric 13, the X axis is in the direction orthogonal to the opening surface 14, and the Y axis is in the direction parallel to the opening surface 14. Each is provided.

In the figure, x1 is the X coordinate value of the point where the curve w on the front surface of the dielectric 13 intersects the X axis, y2 is the Y coordinate value of the upper portion of the dielectric 13, and B is the inclination of the curve w with respect to the Y axis. A point on the Y-axis that defines the boundary between the gentle portion (upper portion) and the portion with a large inclination, P is an arbitrary point on the curve w, h is the normal line at the point P, and L21 is the radio wave incident on the point P. L22 is the traveling direction of the electric wave refracted at the point P toward the outside, α and β are the incident angle and the refraction angle at the point P, and θ is the horizontal direction of the electric wave traveling direction L22 (the positive direction of the X axis). , Θ1 and θ2 are the angles of the refracted radio waves from the horizontal direction at the lower and upper points of the curve w.

The operation and action of the present invention will be described below with reference to FIGS. 1, 2, and 3. From the primary horn 11 shown in FIG. 1, a radio wave whose electric field is horizontally polarized parallel to the upper flat plate 10a or the lower flat plate 10b and whose phase is uniform on the opening surface of the primary horn 11 is radiated. The radio wave radiated from the primary horn 11 is reflected by the reflecting surface 10c, and after reflection, it becomes a plane wave due to the converging action of the parabolic surface of the reflecting surface 10c, and becomes a plane wave.
A circularly polarized wave generator that propagates between
Immediately before 12, it becomes a plane wave over the entire range and enters the circularly polarized wave generator 12.

The circularly polarized wave generator 12 selects a plate width and a plate interval of the parallel metal plate grating 21 at appropriate values so that the phase difference between the electric field parallel to the plate and the electric field perpendicular to the plate is 90 at the output side of the plate. The circularly polarized wave (right-handed circularly polarized wave) is generated at the output side of the circularly polarized wave generator 12 in degrees.

The plane wave that has become circularly polarized enters the dielectric 13. Since the input surface of the dielectric 13, that is, the surface facing the circularly polarized wave generating device 12 is a plane parallel to the aperture plane 14, the circularly polarized plane wave output from the circularly polarized wave generating device 12 is It is vertically incident on the input surface of the dielectric 13. Since the radio wave incident on the dielectric 13 is vertically incident, the traveling direction is not bent by the dielectric, and both the horizontal and vertical polarization components travel in the direction perpendicular to the opening surface 14 and reach the output surface of the dielectric 13. To reach. This output side is the second
As shown in the figure, since it has a section showing a curve w in the XY plane, the radio wave reaching the output surface undergoes a refraction phenomenon when it goes out, and its traveling direction can be changed in the XY plane. . That is, since the angle of the traveling direction depends on the inclination of the curve w, it is possible to change the vertical directivity by changing the shape of the curve w.

This point will be described by using a formula by optically approximating a radio wave.

According to the law of refraction at the point P in FIG. 2, the following equations hold for both vertical and horizontal polarization components.

Where n is the refractive index of the dielectric 13 and ε is the relative dielectric constant of the dielectric 13 with respect to air. Is. From the geometrical condition at the point P, the following formula holds regardless of the plane of polarization.

β−θ = α (3) Next, Y (Y) of the portion where Q (y) contacts the Y axis inside the dielectric 13
Assuming that the power distribution of the horizontal or vertical polarization component along the axis is the same, the reflections for both the horizontal and vertical polarization upon incidence on the dielectric 13 are equal, so the power distribution Q
(Y) is equal for both polarizations. If G (θ) is the vertical power directivity with respect to the horizontal or vertical polarization component, the reflection at the boundary of the curve w is irrespective of the plane of polarization and the inclination angle where the inclination of the curve w with respect to the Y axis is not so large. Since it becomes almost constant, the vertical power directivity G (θ) becomes equal for both polarization components. Further, ignoring the absorption loss in the dielectric 13 as small, the following equation holds for both horizontal and vertical polarization components according to the law of power conservation.

The above-mentioned power distribution Q (y) is the power distribution in the Y direction at the opening of the primary horn 11 and the propagation conditions in the reflecting mirror section 11 (the distance between the upper flat plate 10a and the lower flat plate 10b is radiated from the primary horn 11). If the wavelength is sufficiently larger than the wavelength of the radio wave, the power distribution in the Y direction at the opening of the primary horn propagates between the upper flat plate 10a and the lower flat plate 10b almost as it is.) Is substituted into the above equation (4), and the desired directivity as a modified beam is given to the vertical power directivity G (θ) and substituted into the above equation (4), the left side of the equation (4) is a function of the coordinate y. And the right side of equation (4) is the angle θ
Therefore, the relationship between the angle θ and the coordinate y can be obtained from the equation (4).

Next, from (1), (2), and (3) Since the following equation is obtained, the following equation is obtained by integrating both sides of this equation.

When the relationship between the angle θ and the coordinate y obtained from the equation (4) is used for the integrand on the right side of the equation (6), the left side of the equation (6) is a function of the coordinate x, and the right side of the equation (6). Is a function of the coordinate y, the relationship between the coordinate x and the coordinate y, that is, the shape of the curve w can be obtained from the equation (6). As a practical method of this calculation, a graphic method can be used to perform the calculation relatively easily.

In this way, the curve w that gives the desired vertical power directivity G (θ)
The shape of can be determined.

In the dielectric 13, the propagation phases for the horizontal and vertical polarization components are the same, so the phase relationship between the horizontal and vertical polarization components is that before the input to the dielectric 13 and after passing through the dielectric 13. It won't change later. Therefore, the phase relationship between the horizontal and vertical polarization components at a point sufficiently distant from the aperture plane 14 is maintained as the circular polarization before input to the dielectric 13. Further, according to the above description, the vertical power directivity G (θ) is equal to both the horizontal and vertical polarization components, so that the electric field levels of the horizontal and vertical polarization components are equal at the point far away.

Therefore, within the predetermined angle range, the vertical power directivity G
It can be seen that the phase-amplitude relationship of both the horizontal and vertical polarization components necessary for the circular polarization having (θ) is maintained, and a circular polarization modified beam is obtained.

In the present embodiment, when the desired deformed beam has a directivity in which only one side of the main beam has the cosec square characteristic, the shape of the curve w is with respect to the Y axis corresponding to the main beam shown in FIG. It is divided into an upper part from point B, which has a very gentle inclination, and a part below point B, which corresponds to the cosec-squared characteristic beam and has a large inclination to the Y axis to some extent. In such a case, even if the part above point B is removed, it is not so related to the directivity, so it is also possible to remove this part.

FIG. 3A shows a cross section of the dielectric 13 in the above case. Further, in this case, since the slope of the curve w changes gently, it can be approximated by a polygonal line. Fig. 3 (b)
Is the dielectric 1 when the curve (a) is approximated by straight lines C and D.
The cross-sectional shape of 3 is shown. As described above, in this embodiment, depending on the deformed beam, it is possible to simplify the sectional shape of the dielectric provided near the opening surface 14.

(Effects of the Invention) As described above with reference to the embodiments, according to the present invention,
Only by providing a circularly polarized wave generator made of a parallel metal plate and a dielectric near the aperture of the aperture antenna, a circular polarization is generated within a predetermined angle range within the modified beam in the plane where the thickness of the dielectric is changing. You can get the waves.

Further, the above-mentioned dielectric has a substantially plate-like shape in which the thickness in the opening plane changes only along one direction in the opening plane and the thickness is constant in the direction orthogonal to the direction. It is also easy and cost effective.

Therefore, the present invention can be applied to various radars that search for targets on the ground, at sea, or in the air.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a circular polarized wave modified beam antenna of the present invention, FIG. 2 is a diagram for explaining the operation of the dielectric 13 of FIG. 1, and FIG. 3 is a curve w of FIG. FIG. 4 is a diagram showing an example of linear approximation of FIG. 4, FIG. 4 is a diagram for explaining the structure of the circularly polarized wave generation device of FIG. 1, and FIGS. 5 and 6 are conventional circularly polarized wave modified beam antennas, respectively. It is a figure for explaining. 10 …… Reflector, 11 …… Primary horn, 12 …… Circular polarization generator, 13 …… Dielectric, 14 …… Aperture.

Claims (2)

[Claims] 1. When the aperture plane of an aperture antenna for generating a plane wave is used as the front face and the lower plane plate at the rear of the aperture plane is horizontal, the plane wave is composed of a parallel metal plate grating in which the plane wave is vertically incident. A circularly polarized wave generator is provided, and a thickness X of the circularly polarized wave generator in the direction orthogonal to the opening surface is along the vertical direction parallel to the opening surface, and the height Y of the dielectric is on the opening surface side. Depending on the formula shown below (However, Y: a value indicating the height of the dielectric when the rear lower end of the dielectric is zero and the Y-axis is the direction vertically extending along the opening surface. X: the lower end of the parallel metal plate lattice Is horizontal and the thickness direction with the rear end of the dielectric material that is orthogonal to the opening surface being zero is X.
A value indicating the thickness at the height Y of the dielectric with the axis. X1: Thickness in the X-axis direction at the lower end of the dielectric. θ: Desired beam angle with respect to the horizontal orthogonal to the aperture plane at the height Y of the dielectric substance n: Refractive index of the dielectric substance), and the dielectric substance having the constant thickness is horizontally arranged along the aperture face. A circular polarized wave modified beam antenna characterized by being provided. 2. A circular polarized wave modified beam antenna according to claim 1, wherein a cheese antenna is used as the aperture antenna.