JPH0716129B2 - Dual polarization antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a radar or communication device using microwaves, which is used when switching or simultaneously radiating radio waves of two polarizations orthogonal to each other. It concerns a shared antenna.

(Prior Art) In fields such as radar and communication using microwaves, radio waves of mutually orthogonal polarized waves may be emitted at the same time or for switching. When a horn antenna formed of parallel conductor plates is used in such a case, a polarized wave orthogonal to the parallel conductor plate (hereinafter referred to as a orthogonal polarized wave) and a polarized wave parallel to the parallel conductor plate (hereinafter referred to as a parallel polarized wave). ), The traveling direction of the radio wave may be different when the radio wave is emitted to the outside from the opening of the horn.

2A and 2B are views for explaining the operation of the conventional horn antenna, and the side surfaces of each are composed of two parallel conductor plates. Figure 2a shows the radiation pattern
When a deformed beam having a cosec θ ² characteristic is generated, FIG. 2B shows the paths of radio waves inside and outside the respective horn antennas when the offset feed is performed on the parabolic cylinder type reflecting mirror. .

2a and 2b, 1 and 2 are horn antennas, 1a and 2b are aperture surfaces of the horn antenna, 1b and 2b are equivalent power supply positions, and L ₁ and L ₂ are positions 1b. Alternatively, of the radio waves emitted from 2b and reflected by the reflecting surface in the horn and then radiated to the outside from the opening surface 1a or 2a, the traveling directions are the opening surface 1a, respectively.
Or, it shows the traveling direction of radio waves of orthogonal polarization that is not orthogonal to 2aa. Since this orthogonally polarized radio wave propagates in the TEM mode in the parallel conductor plate of the horn antenna, the guide wavelength in the horn antenna is almost equal to the free space wavelength.
Does not refract when emitted from the opening surface 1a or 1b to the outside,
Continue straight ahead. On the other hand, parallel polarized radio waves propagate in the TE mode (usually TE ₁₀ fundamental mode) in the parallel conductor plate of the horn antenna, so the guide wavelength inside the horn antenna becomes larger than the free space wavelength, and When the refractive index becomes smaller than 1 with respect to the free space and is radiated to the outside from the opening surface 1a or 1b, a refraction phenomenon occurs. 2a and 2b, L ₁ ′ and L ₂ ′ indicate the traveling directions of the parallel polarized radio waves.

In this way, when there is a radio wave whose traveling direction is not perpendicular to the opening surface of the horn antenna, when the radio wave is radiated to the outside from the opening surface, and when it is in the case of orthogonal polarization and parallel polarization, respectively. The direction of travel will differ depending on the radio wave.

(Problems to be solved by the invention) Therefore, in the case of a modified beam as shown in FIG. 2a, the shape of the modified beam becomes different for both polarizations, and as shown in FIG. 2b. When performing offset feed, the main radiation direction will be different for both polarizations, and in both cases circular polarization cannot be obtained because the levels of both polarizations differ within the specified angle range. There is also a problem that even when the two polarized waves are switched to be used, the inconvenience such as a difference in receiving level of radio waves of both polarized waves occurs.

In the horn antenna mainly composed of the parallel conductor plate and the reflecting surface according to the present invention, even when there is a radio wave whose traveling direction is not perpendicular to the opening surface, the radiation direction from each point on the opening surface is orthogonal polarization. It is an object of the present invention to realize a horn antenna that is the same for parallel polarized waves and eliminate the above-mentioned problems in the horn antenna alone or an antenna combined with a parabolic cylinder type reflecting mirror.

(Means for Solving the Problems) The present invention provides a parallel conductor plate on the inner surface of a reflector of a horn antenna such that the traveling direction of radio waves is not perpendicular to the opening as described above. In parallel, a small conductor plate or a plurality of small conductor plates are projected at intervals smaller than 1/2 of the free space wavelength of the radiated radio waves, and the front surface of the small conductor plates forms a reflection surface for parallel polarized waves. Forming and traveling direction when the parallel polarized radio wave reflected by the reflecting surface is refracted and emitted from the opening surface to the free space, and from the opening surface reflected on the inner surface of the reflector to the free space A horn antenna is formed by giving a specific shape to the front edge of the small conductor plate so that the traveling direction of the orthogonally polarized radio wave radiated without refraction matches.

Also, the aperture surface of the horn antenna thus formed is made to coincide with the astigmatic axis of the parabolic cylinder reflecting mirror.

(Operation) According to the present invention, in a horn antenna formed by two parallel conductor plates and a reflector plate facing each other, one or a plurality of small conductors parallel to the parallel conductor plate are provided on the inner surface of the reflector plate along the reflector plate. The plates are projected at intervals, and the intervals are smaller than 1/2 of the free space wavelength of the radiated radio waves.
Of the radio waves propagating in the horn antenna, the radio waves of orthogonal polarization reach and reflect the surface of the reflector regardless of the presence or absence of the small conductor plate, but the radio waves of parallel polarization are the small conductors. It will be reflected at the front edge of the board.

Therefore, the angle of incidence of horizontally polarized radio waves on the aperture plane is formed according to a calculation formula that specifies the shape of the leading edge of the small conductor plate, taking into consideration the refraction angle when the radio waves are radiated into free space. By doing so, since the radiation angles of the radio waves of both polarized waves that are parallel to the right angle can be matched, the above problems can be eliminated.

(Embodiment) FIGS. 1a and 1b are views showing the structure of a horn antenna of the present invention, and FIG. 1a is a side view of an embodiment of the first invention of the present invention, and FIG. FIG. 3 is a sectional view taken along the line AA of FIG.

1 a and b, 10 is a horn antenna, 10a is an opening surface,
Reference numeral 10b denotes a radio wave input surface (this embodiment is used as a transmitting antenna. The same applies hereinafter), 10c is a reflector, 11 is a small conductor plate, and F is a direction perpendicular to a parallel conductor plate forming a horn antenna. Position of equivalent linear power supply, a
Is the distance between the parallel conductor plates. The small conductor plate 11 is provided so as to project in parallel with the parallel conductor plate along the reflection surface of the reflection plate 10c.

FIG. 1c is a view for explaining the operation of the horn antenna of the present invention, showing the plane parallel to the parallel conductor plate of the horn antenna. In FIG. 1c, 11a is the leading edge of the small conductor plate 11, L ₁₀ is the traveling direction of a part of the parallel polarized waves emitted from the position F, and P is the leading edge of the electromagnetic wave. The reflection point on 11a, Q is also the aperture surface 10a of the radio wave.
, L ₁₀ ′ is the traveling direction of the radio wave passing through the output point Q among the orthogonally polarized radio waves emitted from the position F, and P ′ is the reflection point on the surface of the reflection plate 10 c of the radio wave. , P ₁ is a terminal below the front edge 11a, X is a position F as a base point, and the opening surface 1
A straight line extending in the direction perpendicular to 0a, and ρ are the tilt angle and radius of the reflection point P in the polar coordinate system with the position F as the pole and the straight line X as the original line, and α is the output point Q of the radio wave in the traveling direction L _10. Angle of incidence (angle formed with the direction perpendicular to the opening surface 10a), θ is the radiation angle from the output point Q of the radio wave (angle formed with the direction perpendicular to the opening surface 10a), and ₁ and ρ ₁ are respectively The tilt angle and the radius vector of the end point P ₁ in the polar coordinate system.

The operation of the above embodiment will be described with reference to FIGS. 1a, 1b and 1c. In Fig. 1 a and b, the distance a between parallel conductor plates
Is λ / 2 <a <for the free space wavelength λ of the radiated radio wave.
It is assumed that the input surface 10b is a square, the length of each side of which is equal to the interval a. First, the case where parallel polarized radio waves are input to the input surface 10b will be described. When the radio waves propagate near position F, the reflector 10c
And, it is fired toward the front edge 11a. This position F is the leading edge 1
When viewed in the direction of the position F from the vicinity of the center of 1a, the phase center of the propagating radio wave is selected, that is, a position that can be regarded as an equivalent feeding point. The propagation mode in the parallel-polarized horn antenna 10 is the TE ₁₀ mode in the parallel conductor plate, and the guide wavelength is λg. Which is larger than the free space wavelength λ of the radio wave.
Further, since the intervals between the small conductor plates 11 and the intervals between the small conductor plates and the parallel conductor plates are all equal and λ / 2 or less,
The horizontally polarized radio wave cannot be propagated to the inside of the small conductor plate 11 as a cutoff, and is reflected almost at the leading edge 11a. The radio wave reflected here propagates toward the opening surface 10a,
It is radiated into the free space from the opening surface 10a. Since the guide wavelength λg of the radio wave is larger than the free space wavelength λ as described above, when the traveling direction of the radio wave is not perpendicular to the opening surface 10a, it refracts when it is radiated from the opening surface 10a to the free space. Considering the radio wave in the traveling direction L _{10 in} FIG. 1c,
At the output point Q, the following expression (1) is established by Snell's law of refraction.

Here, n is the refractive index when parallel-polarized radio waves are radiated from the inside of the parallel conductor plate into the free space, and is represented by the following equation (2).

The normal line at the reflection point P is ∠FPQ ＝ − according to the law of reflection.
Since α is divided into two and the angle between the tangent line at the reflection point P and the direction perpendicular to the straight line FP is equal to the angle between the normal line at the reflection point P and the straight line FP, that is, (−α) / 2, Equation (3) is established.

Integrating the equation (3) and using the equations (1) and (2), the following equation (4) is obtained.

When the requirement for the directivity of the radio wave radiated from the opening surface 10a is determined, the directivity when the radio wave is emitted from the position F into the parallel conductor plate is known because of the structure near the position F, so The relationship of the radiation angle θ is obtained from the law of power conservation as follows.

That is, the directivity of the power radiated from the opening surface 10a is set to P
(Θ), the directivity of the electric power emitted from the position F is I
(), The tilt angle of the upper end point P ₂ of the front edge 11a of the small conductor plate 11 is
_2, the inclination angle ₁ and the emission angle from the radio wave opening surface 10a corresponding to ₂ respectively theta ₁ and theta _2, and ignoring the reflection of radio waves at the opening face 10a, the inclination ₁ from the position F, an arbitrary point P Since the electric power emitted during the tilt angle is equal to the electric power emitted during the emission angles θ ₁ and θ, the following equation (5) is established.

From the above equation (5), the relationship between the tilt angle and the radiation angle θ can be obtained.
When this relation is applied to the above equation (4), the right side of the equation (4) is expressed as a function of the tilt angle, and the relation between the radius vector ρ and the tilt angle is obtained. Thus, the leading edge from equation (4)
The shape of 11a can be obtained.

Next, the case where a radio wave of orthogonal polarization is input to the input surface 10b will be described. In this case, assuming that the size of the horn antenna 10 is sufficiently larger than the wavelength of the radio wave, the radio wave propagates in the horn antenna 10 in almost the TEM mode, and the in-tube wavelength thereof becomes substantially equal to the free space wavelength λ. Since the plane of polarization of the radio wave is at right angles to the small conductor plate 11, it hardly reaches the influence of the small conductor plate 11, reaches the reflection plate 10c, is reflected by the surface thereof, and reaches the opening surface 10a. Is emitted to. As described above, the guide wavelength of the radio wave is substantially equal to the free space wavelength λ, so that the radio wave is not refracted when radiated from the opening surface 10a to the free space. Therefore, the traveling direction of the orthogonally polarized radio wave that passes through the output point Q in FIG.
L ₁₀ ′ is different from the traveling direction L ₁₀ of the parallel polarized radio wave, and the shape of the curved surface of the reflecting surface of the reflecting plate 10c is small conductor plate 1
The shape of the front edge 11a of 1 is different.

When the radius vector and the tilt angle of an arbitrary point P'on the reflection surface of the reflection plate 10c of the orthogonally polarized wave are ρ'and ', respectively, the following equation (6) is obtained corresponding to the above equation (3).

The following formula (7) is obtained by integrating the formula (6).

Here, ρ ₁ ′ and ₁ ′ are the radius vector and tilt angle of the lower end point P ₁ ′ of the reflection surface of the reflection plate 10c.

Since the relationship between the tilt angle ′ and the radiation angle θ can be obtained as in the case of the parallel polarized wave, the radial ρ ′ can be calculated by the equation (7).
And the inclination angle are required.

That is, it is possible to find the shape of the curved surface of the reflection surface of the reflection plate 10c that is the same when the radiation angle from the opening surface 10a is parallel polarization.

According to the equations (4) and (7), the front edge 11 of the small conductor plate 11 is
radius vector [rho ₁ of the lower end point of the radius vector [rho ₁ or reflecting surface 10c of the lower end point of a _'to the same inclination angle within a predetermined inclination angle by appropriately selecting things, ρ <ρ' It is possible to (However, when the radius vector ρ ₁ or ρ ₁ ′ is changed, the positions for both polarized waves on the aperture plane radiated from the aperture plane 10a at the same radiation angle will be slightly different. Therefore, it can be seen that the small conductor plate 11 can be arranged on the inner front surface of the reflector 10c, and the horn antenna according to the present invention can be physically realized.

FIG. 3 is a block diagram of an embodiment of the second invention of the present invention.
The horn antenna of the embodiment shown in the figure is a feed antenna and a dual polarization antenna.

FIG. 3A shows the configuration in the case of the modified beam, and FIG. 3B shows the configuration in the case of the offset feed. In Figure 3
Reference numerals 12 and 13 are parabolic cylinder type reflecting mirrors, and F ₁ and F ₂ are focal axes of the reflecting mirrors 12 and 13, respectively. With the focal axis F ₁
The lines of intersection between the planes orthogonal to F ₂ and the reflecting mirrors 12 and 13 are parabolas whose focal points are the respective intersections of the planes and the focal axes F ₁ and F ₂ . The lines of intersection between the planes including the focal axes F ₁ and F ₂ and the reflecting mirrors 12 and 13 are straight lines parallel to the focal axes F ₁ and F ₂ , respectively.

In FIG. 3, the horn antenna 10 is placed so that its focal plane F ₁ has its opening near F ₂ . In the case of FIG. 3A, the horn antenna 10 radiates a modified beam of radio waves, which is reflected by the reflecting mirror 12 and then radiated to the outside to form the final beam. The directivity in the plane including the focal axis F ₁ of this final beam is a property of the antenna using the parabolic cylinder type reflecting mirror.Because there is no focusing or diverging action of radio waves in this plane, the directivity of the feed antenna is Will be equal. That is, it is equal to the deformed beam of the horn antenna 10.

In the case of FIG. 3 (b), the horn antenna 10 radiates a radio wave which is inclined upward from the direction perpendicular to the opening surface, the radio wave is reflected by the reflecting mirror 13 and then radiated to the outside to form a final beam. Although formed, the main direction of the final beam is different from the direction perpendicular to the focal axis F ₂ . In the case of FIG. 3B, the front edge 1 of the reflector 10c and the small conductor plate 11 in the horn antenna 10
By applying the above-mentioned means to 1a to form the focal axis
It goes without saying that the final beam in the plane including F ₂ can be used as the deformed beam, that is, the deformed beam at the time of offset feed can be formed.

(Effects of the Invention) As described in detail above, in a horn antenna that is commonly used to radiate radio waves of both polarized waves that are parallel and orthogonal to each other, the traveling direction of the radio waves propagating in the horn antenna is not perpendicular to the opening surface. In this case, the traveling directions of the radio waves radiated to the aperture surface or the free space are different between parallel polarized waves and orthogonal polarized waves. Therefore, along the inner surface of the reflection plate of the horn antenna, one or a plurality of small conductor plates are provided at intervals in parallel with the parallel conductor plates, and the space between the conductor plates is radiated with the free space wavelength of the free space wavelength.
If it is smaller than 112, parallel polarized radio waves are reflected near the front edge of the small conductor plate, but orthogonal polarized radio waves reach the reflection plate and are reflected, so that the shape of the inner surface of the reflection plate is , If the shape of the leading edge of the small conductor plate is formed according to a value calculated by a calculation formula in which specific conditions are entered so that a required radiation pattern is obtained, radio waves of both parallel and orthogonal polarizations can be obtained. , The radiation angle from the opening surface to the free space can be made equal. Accordingly, when the modified beam, the offset feed or the offset feed of the modified beam is applied to the dual polarization antenna configured by combining the horn antenna alone or the horn antenna and the parabolic cylinder reflecting mirror, the parallel beam is applied when the present invention is applied. The beam shape and the main radiation direction for both polarizations orthogonal to can be made substantially equal. This makes it possible to eliminate the conventional inconvenience caused by the difference in the beam shape or the main radiation direction for both polarized waves when radiating the circular polarized wave or when switching and radiating the both polarized waves. As described above, the present invention is most effective when applied to the fields such as radar and communication using microwaves.

[Brief description of drawings]

1a is a side view of an embodiment of the first invention of the present invention, FIG. 1b is a sectional view taken along the line AA of FIG. 1a, and FIG. 1c is for explaining the operation of the horn antenna of the present invention. FIG. 2 is a diagram for explaining the operation of the conventional horn antenna, and FIG. 3 is a configuration diagram of an embodiment of the second invention of the present invention. 1,2 ... Horn antenna, 1a, 2a ... Aperture surface, 1b, 2b ... Equivalent power supply position, 10 ... Horn antenna, 10a ... Aperture surface, 1
0b: Radio wave input surface, 10c: Reflector, 11 ... Small conductor plate, 12, 13
... reflector, F ... position of equivalent power feeding source, F _1, F ₂ ... focal axis, a ... distance parallel conductor plates.

Claims (2)

[Claims] 1. A position equivalent to a power supply source of a horn antenna, which has an opening face and is composed of two parallel conductor plates facing each other and a reflector plate formed so as to obtain a required radiation characteristic. , Propagating in the horn antenna all or a part of the radio waves propagating through the reflector, the radio waves being polarized in parallel or at right angles to the parallel conductor plate and radiating to the free space from the opening surface. In a dual-polarization antenna whose direction is not at right angles to the aperture plane, along the reflector on the inner surface of the reflector, parallel to the parallel conductor plate, from 1/2 of the free space wavelength of the radiated radio wave. A small conductor plate or a plurality of small conductor plates are provided at small intervals so that the front edge of the small conductor plate forms a reflection surface for the radio waves of the parallel polarization, and the parallel polarization emitted from the position of the power supply source. The wave of the wave is reflected by the reflecting surface,
Direction of travel when the light is refracted and radiated from the opening surface into the free space, and the traveling of the orthogonally polarized radio wave reflected by the inner surface of the reflector and radiated from the opening surface to the free space without refraction A dual-polarization antenna, wherein a horn antenna is formed by giving a specific shape to the front edge of the small conductor plate so that the directions thereof match. 2. A position equivalent to a power supply source of a horn antenna having an opening surface and comprising two parallel conductor plates facing each other and a reflecting plate formed so as to obtain a required radiation characteristic. , Propagating in the horn antenna all or a part of the radio waves propagating through the reflector, the radio waves being polarized in parallel or at right angles to the parallel conductor plate and radiating to the free space from the opening surface. In a dual-polarization antenna whose direction is not at right angles to the aperture plane, along the reflector on the inner surface of the reflector, parallel to the parallel conductor plate, from 1/2 of the free space wavelength of the radiated radio wave. A single or a plurality of small conductor plates are projected at small intervals, and the front edge of the small conductor plate forms a reflection surface for the parallel polarized radio waves, and the parallel polarized waves radiated from the position of the power supply source. Radio waves from the aperture surface So that the traveling direction when refracted to be radiated to and the traveling direction of the orthogonally polarized radio wave that is reflected by the inner surface of the reflection plate and radiated from the opening surface to the free space without being refracted A dual-polarization antenna, characterized in that the opening surface of a horn antenna formed by giving a specific shape to the front edge of the small conductor plate is made to coincide with the focal point axis of the parabolic cylinder reflecting mirror.