JP2803433B2 - Reflected wave absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber, and more particularly to an absorber for absorbing a reflected wave from an obstacle such as a building.

[0002]

2. Description of the Related Art As a conventional reflected wave absorber, there is the following one. The first is a reflected wave absorber using a dielectric material, and FIG. 5 shows one example. In the figure, a dielectric 22 processed in a tapered shape is integrally provided on the surface of a conductor plate 23. Here, graphite powder is mainly used as a material that causes energy loss of electromagnetic waves. In order to hold this lossy material in the space, a method of applying paper or a Teflon sheet to the dielectric surface, a method using styrene foam,
A method of mixing in a dielectric material such as urethane foam or rubber has been adopted. When the matrix is determined, the dielectric constant of the absorbent material by the graphite amount _{ε r (= ε r '-jε} r ") is changed.

In this absorber, the wave impedance η and the propagation constant γ for a plane wave are expressed by the following equations. η = η _O / (ε _r ) ^1/2 (1) γ = α + jβ = jk _O (ε _r ) ^1/2 (2) where η ₀ , k ₀ : wave impedance and constant attenuation constant in vacuum When α is increased, | η | becomes smaller than η ₀ from the equation (1), so that when a radio wave is incident from a vacuum on a flat plate made of this material, large reflection occurs. Therefore, the absorber when this dielectric material is used is processed into a tapered shape as shown in FIG.
Although the shape is planar, various ε _r values are prepared and they are layered.

[0004] Part 2 is a reflected wave absorber using a magnetic material, and FIG. 6 is a shape diagram showing one example thereof. In the figure, a magnetic body 24 is integrally provided on the surface of a conductor plate 23. Here, a magnetic material is used as a material that causes energy loss of electromagnetic waves. The magnetic material is f = f
Before and after _r , the value of the loss term μ ″ is large, and it can be a reflected wave absorber. A conductor plate is attached to one surface of a flat magnetic material, and a plane electromagnetic wave is vertically incident from the other surface. when examining the reflection coefficients by changing the f, in the case of. magnetic material and a matching thickness d _m of the reflection coefficient makes it 0 matching frequency f _m Gatada pair exists μ is the reflection coefficient for changes greatly with frequency The frequency characteristic is a narrow band type, and although not shown, a reflected wave absorber 3 using a tree such as a hardwood or a conifer, which is not shown in the figure, has a characteristic that leaves of the tree scatter and absorb electromagnetic waves. It was used.

[0005]

The above-mentioned conventional reflected wave absorbers have the following problems. As shown in FIG. 5, the first one uses a dielectric material as a base material, and a material having σ, such as graphite powder mixed or coated, is used as an absorber, but has a broadband characteristic as shown in FIG. However, it cannot absorb low frequencies. In addition, the total thickness of the absorber is required to be about 1.3 times the minimum operating wavelength, and the thickness becomes considerably large. Furthermore, there is a problem that the price is high because a dielectric material is used and the shape is complicated.

The second type shown in FIG. 6 uses a magnetic material as it is or a powder mixed with another material, such as rubber, as an absorber, but as shown in FIG. Higher frequency cannot be absorbed due to band characteristics.
Further, the total thickness of the absorber is considerably reduced to about 0.26 times the minimum operating wavelength as compared with the case of the dielectric material, but there is a problem that the price is high.

The third one uses the scattering and absorption characteristics of the leaves of a tree. For example, f = 332 MH
_As can be seen from the experimental value of the attenuation of about 30 dB per 100 feet in the UHF band of _Z , the total thickness of the absorber becomes considerably thicker. Further, the scattering and absorption characteristics change depending on the state of the leaves of the tree, that is, the degree of drying and moisture. Furthermore, in order to form a tree layer, there is a problem that a vast site is required in front of a building or the like, and the maintenance cost of the tree is high. An object of the present invention is to provide a thin and low-cost reflected wave absorber that can absorb a reflected wave regardless of a frequency band.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a plurality of quarter cylinders having a radius one quarter of the wavelength used by the transmitting antenna and having an appropriate length perpendicular to the plane of polarization of the transmitting antenna. And a reflector mounting position adjusting means for adjusting the distance between the centers of the plurality of quarter-cylindrical reflectors. Here, when the radiation pattern of the transmitting antenna is broad, the center interval D of the quarter-cylindrical reflector is set to D ≒ X · Y / (Y−λ / 4) −X. X is the distance from the phase center of the transmitting antenna to the center of the quarter cylindrical reflector, and Y is the distance from the phase center of the transmitting antenna to the reflector mounting position adjusting means. In the case where the radiation pattern of the transmitting antenna is sharp and the reflected wave due to a specific side lobe is absorbed, the center of the quarter-cylindrical reflector is almost coincident with the position where the maximum energy of the side lobe hits an obstacle.

[0009]

Next, the present invention will be described with reference to the drawings. FIG. 1 is an external view of one embodiment of the reflected wave absorber of the present invention,
FIG. 2 is a layout diagram when this reflected wave absorber is installed in an actual airport or the like. In these figures, the reflected wave capturing unit has a radius 1A to about 1/4 of the used wavelength of the transmission antenna 7.
1N, consisting of a plurality of quarter-cylindrical reflectors 3A-3N having an appropriate reflector length 2. Here, the reflector length 2 is longer in the direction perpendicular to the polarization plane of the transmitting antenna 7. These plurality of quarter-cylindrical reflectors 3A to 3N
Are attached to the reflector mounting position adjusting plate 6, and the adjusting plate 6 controls the centers 4A to 4A of the reflectors 3A to 3N.
It is configured so that the position of 4N can be changed and adjusted. still,
In FIG. 2, 7 is a transmitting antenna, 9 is a runway, and 10 is an obstacle.

The reflecting plate mounting position adjusting plate 6 is
If the radiation pattern of the transmitting antenna 7 is broad,
The quarter-quarter cylindrical reflector intervals 5A to 5 (N-1) are set so that the intervals at which the reflected waves can be continuously captured most effectively, that is, the intervals represented by the equation (3), are set to four quarters. 1. Adjust the mounting positions of the cylindrical reflectors 3A to 3N. D ≒ X · Y / (Y−λ / 4) −X (3) where X: distance 11 from phase center 8 of transmitting antenna 7 to center 4A of quarter-cylindrical reflector, Y: A distance 12, from the phase center 8 of the transmitting antenna 7 to the reflector mounting position adjusting plate 6,
D: An interval between the quarter-cylindrical reflecting plates 3A to 3N.

If the radiation pattern of the transmitting antenna 7 is sharp and the reflected wave by a specific side lobe is absorbed, the center of the quarter cylindrical reflector is located at a position where the maximum energy of the side lobe hits the obstacle 10. The mounting positions of the quarter-cylindrical reflectors 3A to 3N are adjusted so that 4A to 4N substantially match.

In the reflected wave absorber configured as described above, as shown in FIG. 3, the incident wave 1 radiated from the transmitting antenna 7
3A is a quarter-cylindrical reflecting plate center 4A, that is, an optical center, which reflects while maintaining the relationship of incident angle 14A = reflection angle 15A,
It becomes a reflected wave 16A. The reflected wave 16A is reflected again on the surface of the quarter-cylindrical reflecting plate 3A and becomes a reflected wave 17A.
The reflected wave 18A is formed through the third reflection at the center 4A of the 1 / th cylindrical reflector, and is reflected in the direction opposite to the incident wave 13A.

Here, a combined vector diagram of the incident wave and the reflected wave is as shown in FIG. The reflected wave 18A is the incident wave 13
The amplitude of A is almost the same as that of A, but the phase is different by 180 °, so that the synthesized wave 19A is almost zero. This is reflected wave 18
This means that A has been canceled by the incident wave 13A. The reason why the reflected wave 18A has a phase difference of 180 ° with respect to the incident wave 13A is that a quarter cylindrical reflector radius 1A is formed at a quarter of the wavelength used by the transmitting antenna 7, that is, 90 °. Because it is.

On the other hand, an incident wave 13A radiated from the transmitting antenna 7 and incident at a position slightly shifted from the center 4A of the quarter-cylindrical reflector 4A undergoes multiple reflection inside the quarter-cylindrical reflector 3A. FIG. 4B shows an example of a composite vector diagram when the incident wave 13A is repeatedly reflected in the opposite direction. In this case, the reflected wave 20A is four times larger than the incident wave 13A.
The amplitude is attenuated by the amount of the multiple reflections inside the one-third cylindrical reflector 3A, and the phase is slightly shifted from 180 °. Since the composite wave 21A of the incident wave 13A and the reflected wave 20A is completely canceled and does not become 0, the remaining component becomes the incident wave again and the same multiple reflection process as described above is repeated. As a result, the reflected wave component is attenuated to an almost negligible level.

[0015]

As described above, according to the present invention, a plurality of quadrants having an appropriate length in the direction perpendicular to the plane of polarization of the transmitting antenna with a radius of one-fourth of the operating wavelength of the transmitting antenna. A reflected wave capturing means comprising a single cylindrical reflector; and a reflector mounting position adjusting means for adjusting the distance between the centers of the plurality of quarter cylindrical reflectors, thereby providing a low frequency band. There is an effect that a reflected wave from an obstacle such as a building can be absorbed or sufficiently attenuated from a high frequency band to a high frequency band. In particular, it is effective in a low frequency band where the reflection and absorption effect is poor. Further, it is possible to obtain a reflected wave absorber in which the total thickness of the absorber is as thin as about 0.25 times the transmission wavelength, at a low cost.

[Brief description of the drawings]

FIG. 1 is an external view of one embodiment of a reflected wave absorber of the present invention.

FIG. 2 is a plan view of an example in which the reflection absorber of FIG. 1 is arranged at an airport or the like.

FIG. 3 is a sectional view of a quarter-cylindrical reflector;

FIG. 4 is a combined vector diagram of an incident wave and a reflected wave in a quarter cylindrical reflector.

FIG. 5 is an external view of a first example of a conventional reflected wave absorber.

FIG. 6 is a second external view of a conventional reflected wave absorber.

FIG. 7 is a frequency characteristic diagram of a conventional reflected wave absorber.

[Explanation of symbols]

 3A-3N Quarter-cylindrical reflector 4A-4N Center of quarter-cylindrical reflector 5A-5 (N-1) Center spacing of quarter-cylindrical reflector 6 Reflector mounting position adjustment plate 7 Transmission antenna 10 Obstacle

Claims (3)

(57) [Claims] 1. A reflected wave comprising a plurality of quarter-cylindrical reflectors having a radius one-fourth of a wavelength used by a transmitting antenna and having an appropriate length in a direction perpendicular to the plane of polarization of the transmitting antenna. A reflected wave absorber comprising: a capturing means; and a reflector mounting position adjusting means for adjusting a distance between respective centers of the plurality of quarter-cylindrical reflectors. 2. The reflected wave absorber according to claim 1, wherein when the radiation pattern of the transmitting antenna is broad, the center distance D of the quarter-cylindrical reflector is set as follows. D ≒ X · Y / (Y−λ / 4) −X where X: distance from the phase center of the transmitting antenna to the center of the quarter cylindrical reflector, Y: mounting position of the reflector from the phase center of the transmitting antenna This is the distance to the adjusting means. 3. When the radiation pattern of the transmitting antenna is sharp and the reflected wave due to a specific side lobe is absorbed, the center of the quarter-cylindrical reflector is located at a position where the maximum energy of the side lobe hits an obstacle. 2. The reflected wave absorber according to claim 1, which is matched.