JPH11121972A - Reflected radio wave scattering structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily inexpensively reduce the amount of reflected radio waves from a turbine wheel which is positioned in an intake duct. SOLUTION: A turbine wheel 2 is disposed in an intake duct 1 of an aircraft. Two conductor meshes 3 and 4 are arranged with a prescribed interval in between in front of the wheel 2 in the duct 1. The meshes 3 and 4 are respectively arranged tilting at prescribed angles from a plane perpendicular to the arriving direction of radio waves. The openings 3a and 4a of the meshes 3 and 4 are formed into square shapes and the sizes of the openings 3a and 4a are set so that the ratio of the circumferential length L1 =4l1 of each of the openings 3a to the peripheral length L2 =4l2 of each of the openings 4a become mutually differing prime numbers, when the ratio is expressed in a natural number. L1 and l2 respectively represent the lengths of one sides of the openings 3a and 4a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave reflector disposed inside a cylinder, and more particularly, to a reflected radio wave scattering structure of a Durbin wheel disposed in an intake duct of an aircraft.

[0002]

2. Description of the Related Art Referring to FIG. 4, a turbine wheel b disposed inside an intake duct a of an aircraft is a good reflector for electromagnetic waves such as radars, so that a very large reflected wave comes in the direction of arrival. And sometimes lead to undesirable results. Therefore, in order to reduce the reflected wave from the turbine wheel b, for example, an orifice c (see FIG. 5) or a conical cover is provided at the air intake of the intake duct a to scatter most of the incoming radio waves, or A method has been proposed in which a portion of the duct a located in front of the turbine wheel b is bent to scatter most of the incoming radio waves (see FIG. 6).

[0003]

However, the former reflected radio wave scattering structure shown in FIG. 5 has disadvantages in that the aug c is expensive in terms of cost and that the air inflow from the air intake is obstructed. Further, in the latter reflected radio wave scattering structure shown in FIG. 6, the bending of the intake duct a is costly in terms of work, and the bent shape has another function (for example, smooth supply of air to the engine unit). There is an inconvenience that it is often difficult to realize due to suppression.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a reflected radio wave scattering structure capable of reducing the reflected radio waves from a radio wave reflector at a simple and low cost.

[0005]

In order to achieve the above object, a reflected radio wave scattering structure according to claim 1 is a reflected radio wave scattering structure of a radio wave reflector disposed inside a cylinder,
A plurality of conductor meshes provided at a predetermined interval in front of the radio wave reflector in the cylinder are arranged at a predetermined angle with respect to a plane perpendicular to the direction of arrival of radio waves, and further, each conductor mesh Are characterized in that they have openings of a certain size, and are different prime numbers when the ratio of the perimeters of the openings of the respective conductor meshes is expressed by a natural number.

According to a second aspect of the present invention, there is provided the reflected radio wave scattering structure according to the first aspect, wherein the natural numbers having different prime numbers are 5 or more.
It is characterized by the above.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory cross-sectional view for explaining a reflected radio wave scattering structure according to an embodiment of the present invention.
Is a partial plan view of a conductor mesh, and FIG. 3 is a partial plan view of another conductor mesh. In this embodiment,
As an example, an intake duct of an aircraft is used as a cylinder, and a turbine wheel disposed inside the intake duct is used as a radio wave reflector.

In FIG. 1, reference numeral 1 denotes an intake duct (tubular body) of an aircraft, and a turbine wheel (radio wave reflector) 2 is disposed inside the intake duct 1. Two conductor meshes 3 and 4 are provided at predetermined intervals at a position in front of the turbine wheel 2 in the intake duct 1. Each of the conductor meshes 3, 4 is inclined at a predetermined angle with respect to a plane perpendicular to the arrival direction of the radio wave, and
The conductor mesh 3 and the conductor mesh 4 are arranged so as not to be parallel to each other.

As shown in FIGS. 2 and 3, a plurality of openings 3a and 4a of each of the conductor meshes 3 and 4 are formed in a square shape having a fixed size, and the length of one side is defined as the opening. 3a, respectively When l _1, l ₂ for 4a, the circumferential length of the opening 3a L ₁ = 4l ₁ and the circumferential length of the opening 4a L ₂ =
When the ratio with 4l ₂ is represented by a natural number, the prime numbers are set to be different from each other.

Here, the conductor meshes 3 and 4 having a fixed opening size function as a kind of frequency selection film, and the circumference L and the wavelength λ are approximately L = nλ (or the frequency f = c /
λ (c is the speed of light)), and resonates at a wavelength having a relationship of λ (c is the speed of light) and transmits electromagnetic waves. Then, radio waves of other frequencies are totally reflected. Here, n is a natural number.

Therefore, the arriving radio wave entering from the air intake of the intake duct 1 is f _{0 in the} conductor mesh 3.
The transmitting the electromagnetic wave of the multiplied wave nf ₀ to base (or λ = 4l ₁ / n), but waves otherwise never returning to the arrival direction is totally reflected obliquely.

Also, the waves f ₀ ,
nf ₀ (waves other than λ = 4l ₂ / n) is totally reflected obliquely by the conductor mesh 4 in the same manner as described above, and does not return in the arrival direction. Conductor mesh 4 has a different opening dimension conductor mesh 3, moreover, at different prime when the ratio of the circumferential length L ₁ of the circumferential length L ₂ and the opening 3a of the opening 4a is expressed in natural numbers since there is essentially conductor mesh 4 is totally reflected against multiplication waves nf ₀ to base the f _0.

However, since the wave having the least common multiple of the opening dimensions of the openings 3a and 4a is transmitted through the conductor mesh 4, it is preferable that the above-mentioned natural numbers having different prime numbers be 5 or more. Then L ₁ : L ₂ =
7: 5. Since the transmission characteristics of the multiplied wave of 5 times or more are greatly reduced, the wave reflected by the turbine wheel 2 is considerably attenuated even if it passes through both the conductor meshes 3 and 4, so that there is no practical problem.

As described above, in the reflected radio wave scattering structure of this embodiment, two conductor meshes 3 and 4 having frequency selectivity are disposed inside intake duct 1 regardless of the shape of intake duct 1. With only this, the reflected wave from the turbine wheel 2, which is a radio wave reflector, can be scattered so as not to return to the arrival direction, so that the effect of reducing the reflected wave can be obtained simply and at low cost.

Since the ratio of the circumference L ₁ of the opening 3a of the conductor mesh 3 to the circumference L ₂ of the opening 4a of the conductor mesh 4 is a natural number which is 5 or more when expressed as a natural number, The transmission characteristic of the wave which is the least common multiple of the opening size of the openings 3a and 4a can be significantly reduced, and the wave reflected by the turbine wheel 2 can be considerably attenuated. As a result, the reflected wave of the turbine wheel 2 can be reduced. The reduction effect can be made more reliable.

Furthermore, since the structure in which the meshes 3 and 4 are disposed inside the intake duct 1 is adopted, the air passage from the air intake of the intake duct 1 is straightened to reduce the suction resistance. be able to.

The material of the conductor meshes 3 and 4 may be a conductor such as a metal wire, a metal plate, a metal fiber, a carbon fiber, or a ceramic fiber having a low specific resistance.
It is possible to apply a dielectric material such as a conductive material by conducting a conductive coating.

The shape of the conductor meshes 3 and 4 is not limited to a mesh shape, and may be a plate material having a slot in a plate material. Furthermore,
In the above embodiment, the openings 3 of the conductor meshes 3 and 4 are formed.
Although a and 4a have a square shape, they are not limited to this.
For example, the openings 3a and 4a may be rectangular or other shapes. Since the resonance mode of the prime number is different in an aperture shape other than a square, the frequency of the transmitted wave is derived by a different equation.However, in the present invention, all the waves are scattered by providing a plurality of conductor meshes in parallel, so that Determining the resonance frequency is not important.

[0019]

As is apparent from the above description, according to the first aspect of the present invention, two conductor meshes having frequency selectivity are arranged inside the cylindrical body regardless of the shape of the cylindrical body. With only this, the reflected wave from the radio wave reflector can be scattered so as not to return to the arrival direction, so that the effect of reducing the reflected wave can be obtained simply and at low cost.

According to the second aspect of the present invention, in addition to the first aspect, the transmission characteristic of a wave which is the least common multiple of the opening size of the opening of each conductor mesh is greatly reduced, and the wave is reflected from the radio wave reflector. Since the wave can be considerably attenuated, the effect of reducing the reflected wave from the radio wave reflector can be further ensured.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view illustrating a reflected radio wave scattering structure according to an embodiment of the present invention.

FIG. 2 is a partial plan view of a conductor mesh.

FIG. 3 is a partial plan view of another conductor mesh.

FIG. 4 is an explanatory sectional view used for explaining a conventional example.

FIG. 5 is an explanatory cross-sectional view for explaining a conventional reflected radio wave scattering structure.

FIG. 6 is an explanatory cross-sectional view for explaining another conventional reflected radio wave scattering structure.

[Explanation of symbols]

1 ... intake duct (tubular body) 2 ... turbine wheel (wave reflector) 3,4 ... conductor mesh 3a, 4a ... opening 4l _1, 4l ₂ ... circumference

Claims (2)

[Claims] 1. A reflected radio wave scattering structure of a radio wave reflector disposed inside a cylinder, wherein a plurality of radio wave reflection structures are provided at predetermined positions in front of the radio wave reflector in the cylinder. The conductor mesh is arranged at a predetermined angle with respect to a plane perpendicular to the arrival direction of the radio wave, and further, each conductor mesh has a plurality of openings each having a fixed size, and the opening of each conductor mesh is formed. A reflected radio wave scattering structure characterized in that when the ratio of the perimeters is represented by a natural number, they are different prime numbers from each other. 2. A natural number which is a different prime number is 5
The reflected radio wave scattering structure according to claim 1, wherein: