JPH07111337B2 - Scattering cross section calculator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scattering cross-section calculating apparatus for calculating a scattering cross-section of a target.

[Prior Art] FIG. 10 shows, for example, 1989 IEEE AP-S International Sympos
FIG. 8 is a diagram showing a conventional scattering cross-section calculation device written with reference to the one shown in ium p.848-851. In the figure,
(1) is a scattering cross-section calculation device, (2) is a shape approximation means for approximating a target with a simple shape such as a plate, a cylinder, or a sphere,
(3) is a ray trace searching means for performing ray tracing based on the principle of minimum optical path length, and (4) is a ray trace searching means (3).
Diffraction wave calculation means for calculating each diffraction wave by the geometrical optical diffraction theory based on the ray trajectory obtained in step (5) is scattered by the square of the sum of each diffraction wave obtained by the diffraction wave operation means (4). It is a scattering cross-section calculation means for obtaining the cross-section.

Next, the operation will be described.

The shape approximation means (2) approximates the shape of the target with a flat surface, a cylindrical surface, a conical surface, a spherical surface, or the like. Next, ray trace searching means (3)
Ray-trace based on the principle of minimum optical path length for the approximate target and given incident and observation directions at. That is, when a light ray is applied to the target from the incident direction of the radio wave, it is reflected by the surface of the target and reaches the observation direction, and is diffracted by the ridgeline of the target, and reaches the observation direction, and the surface is diffracted on the uneven surface of the target. The trajectories of light rays reaching the observation direction and light rays reaching the observation direction through reflection, diffraction, and surface diffraction are obtained. Next, in the diffracted wave computing means (4), the geometrical optical diffraction theory is applied to the trajectory of each ray found by the ray trajectory searching means (3) to find the diffracted wave from the target, and the scattering cross section computing means (5 ), The scattering cross section of the target is obtained by the square of the sum of those diffracted waves.

[Problems to be Solved by the Invention] Since the conventional scattering cross-section calculation apparatus is configured as described above, it is not possible to accurately calculate the scattering cross-section by accurately approximating a target having a complicated shape. There was a problem that it was difficult. Furthermore, in order to accurately approximate a target with a complicated shape, it is necessary to combine many simple shapes, which requires a lot of calculation time for the ray trajectory search, which is not practical. It was

The present invention has been made to solve the above problems, and even a target having a complicated shape can easily approximate a polyhedron with a necessary and sufficient accuracy, and the scattering cross section can be accurately calculated in a short calculation time. It is an object of the present invention to obtain a scattering cross-section calculation device that can be calculated.

[Means for Solving the Problem] A first scattering cross-section area calculating apparatus according to the present invention sets a virtual line that divides a target into a plurality of individuals on the surface of the target, and divides the target by the virtual line. When points are set on the circumference of the cross section of each individual at approximately the wavelength interval of the radio wave used, the points set for each individual are connected immediately before, and the target of the individual divided by the above virtual line Form a plurality of triangles on each surface to form a plurality of triangles on the surface of the target, and define a polyhedron approximation means that approximates the target with a polyhedron, and all sides visible from the incident direction of the polyhedron approximated by this polyhedron approximation means. A unit vector having the same angle between the edge searching means to be searched and the incident direction existing in each surface of the two surfaces sharing this edge in each edge searched by the edge searching means and the angle with the observation direction. Unit vector performance Calculating means, an equivalent wave source calculating means for obtaining an equivalent wave source having the direction of this unit vector to be provisionally provided on each side, and a diffracting wave calculating means for obtaining a diffracted wave in the observation direction radiated from this equivalent wave source, A scattering cross section calculating means for calculating a scattering cross section from the sum of the diffracted waves is provided, and the scattering cross section of the target is calculated.

The second scattering cross section computing device according to the present invention is
A polyhedral approximation means for approximating the target with a polyhedron, a side search means for searching all sides visible from the incident direction of the polyhedron approximated by the polyhedron approximation means, and each side searched by this side search means, sharing this side And a unit vector calculation means for obtaining a unit vector having the same angle between the incident direction and the observation direction existing in each of the two surfaces, and the direction of this unit vector to be provisionally provided on each side. An equivalent wave source calculation means for obtaining an equivalent wave source having, a diffracted wave calculation means for obtaining a diffracted wave emitted from the equivalent wave source in the observation direction, and a scattering cross section calculation means for obtaining a scattering cross section from the sum of the diffracted waves. And the scattering cross section of the target is calculated when the direction of incidence of radio waves coming from sufficiently far away to the target and the direction of observation of an observation point far away from the target are different. It is intended to.

[Operation] In the scattering cross-section calculation apparatus of the present invention, in the polyhedron approximation means, a virtual line that divides the target into a plurality of individuals is set on the surface of the target, and each individual is obtained by dividing the target with the virtual line. Set points at approximately the wavelength intervals of the radio waves used on the circumference of the cross section, connect the points set for each individual with a straight line, and divide multiple points for each target surface divided into each individual with the above virtual line. A triangle is formed to form a plurality of triangles on the surface of the target, and a target having a complicated shape is approximated by a polyhedron without twisting with sufficient and sufficient accuracy. Further, the polyhedral approximation means approximates the target with a polyhedron, the side search means searches all the sides of this polyhedron that are visible from the incident direction, and the equivalent wave source calculation means has the unit vector direction obtained by the unit vector calculation means. A line electromagnetic current source is temporarily installed on all visible sides, and the diffracted wave calculation means obtains a radiation field from these equivalent line electromagnetic current sources.
The scattering cross section calculating means calculates the sum of these to calculate the scattering cross section, and accurately calculates the scattering cross section in the target arbitrary observation direction in a short calculation time without diverging.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of a scattering cross-section calculating apparatus of the present invention. In the figure, (6) is a polyhedron approximating means for approximating the target with a polyhedron, (7) is an edge searching means for searching for all the edges visible from the incident direction of the radio waves of the polyhedron approximated by the polyhedron approximating means (6), (8) is a unit vector calculation means for obtaining a unit vector existing on each of the two surfaces forming each side for each side found by the side search means (7), and (9) is a side search means ( Equivalent wave source calculation means for obtaining the equivalent wave source having the two unit vector directions obtained by the unit vector calculation means (8) for the two surfaces constituting the side to be provisionally provided on each side obtained in 7), (10) Is a diffracted wave operation means for calculating the diffracted wave radiated from the wave source obtained by the equivalent wave source operation means (9), and (11) is the square of the sum of the diffracted waves obtained by the diffracted wave operation means (10). It is a scattering cross-section calculation means for obtaining the cross-section.

The operation of the scattering cross-section calculation apparatus configured as described above will be described with reference to the flowchart of FIG. In addition,
Here, the aircraft shown in FIG. 3 will be described as an example.

First, the polyhedral approximation means (6) will be described. First, as shown in FIG. 4, an imaginary line indicated by broken lines A, B, C, D, etc. is set in FIG. 4 for dividing the aircraft into a plurality of solids. (Step S1) The intervals of this division are rough when the shape change of the aircraft is small and fine when the shape change is large. However, the above division may be equally spaced. As shown in FIG. 5, points are determined on the circumference of the cross section of each individual when the aircraft is divided by virtual lines, at intervals of about the wavelength of the incident radio wave. (Step S2) However, if the change in cross-sectional shape is small, points may be determined at wide intervals with respect to the wavelength of the incident radio wave. Next, as shown in FIG. 6, the points determined in FIG. 5 are connected by straight lines to form a large number of triangles. Similar operations are performed for other divided aircraft body parts to approximate the aircraft with a polyhedron. (Step S3) However, not only a triangle but also a polygon such as a quadrangle may be used. The triangle is the minimum unit of a polygon, and has an advantage that a target having a complicated shape can be easily and accurately approximated without twisting the surface.

Next, the edge search means (7) will be described. The polyhedron shown in FIG. 7 will be described as an example. Now, suppose that radio waves enter from the upper front of the figure. (However, the front is the side L2 in Fig. 7,
The surface is composed of L15, L18, and L16. ) At this time, the sides visible from the incident direction of the radio waves are L1, L2, L3, L4, L5, L6,
L7, L8, L9, L10, L11, L13, L15, L16, L18. Note that L4 and L5 are considered as separate sides. The same operation is performed for a polyhedron that is a polyhedron approximation of the aircraft shown in FIG. 3 and a visible side is searched. (Step S4) Next, the unit vector calculation means (8) will be described. FIG. 8 shows the portion forming the side L2 in FIG. The method of obtaining the assumed unit vector on the side L2 will be described below. In FIG. 8, the incident direction of the radio wave is a vector 'and the observation direction is a vector. The unit vector ₁ existing in the plane 1 where the angles formed by the incident direction vector 'and the observation direction vector are equal to each other are obtained by the following formula. (Step S5) (− ′) · ₁ = 0 (1) Similarly, the unit vector ₂ existing in the plane 2 where the angles formed by the incident direction vector ′ and the observation direction vector are equal to each other is calculated by the following equation. . (Step S6) (- ') · 2 = 0 (2) for each side on visible aircraft of FIG. 3 in such a way from the incident direction of the radio wave of the polyhedra polyhedral approximation obtaining a unit vector.

Next, the equivalent wave source calculation means (9) will be described. Using the unit vector obtained by the unit vector calculation means (8), among the equivalent wave sources to be provisionally provided on the side having the direction of this unit vector, the one having the direction of vector ₁ in the plane 1 is the following method. Ask in. FIG. 9 is a diagram for explaining the method of obtaining, and FIG. 9 (a) shows a part of FIG. 6 taken out. Vector ₁ in the figure indicates a unit vector at a point Q on the side. FIG. 11B is a diagram showing the relationship between the vector _{1 at the} point Q, the incident direction vector ', and the observation direction vector. In the figure β ₁ is a unit vector
₁ and the incident direction vector ′ are shown, and the vector ▲ ^′ ₁ ▼ and the vector ₁ are vector ′ respectively.
And a unit polarization vector orthogonal to the vector. FIG. 13C is a diagram projected on a cross section taken at the position of the point Q as shown by the alternate long and short dash line in FIG. Γ in the figure is the ninth
It is an angle formed by the surface 1 and the surface 2 in FIG. In the figure, vector ▲ ^′ ₁ ▼ and vector ₁ are unit polarization vectors orthogonal to vector ′ and vector, respectively. Here, the vector ▲ _^'1 ▼, vector ₁ and vector ^▲' ₁ ▼, vector ₁ and vector ', the relation between the vector is represented by the following formula.

′ ＝ ▲ ^′ ₁ ▼ × ▲ ^{′ ′} ₁ ▼ (3) = ₁ × ₁ (4) At point Q, the current source component of the equivalent electromagnetic current source is I ₁ , and the magnetic current source component is
M ₁ is obtained by expanding the conventional equivalent electromagnetic flow source derived from the diffracted wave by the geometrical optical diffraction theory by the following equations. (Step S7) However, Here, ⁱ is the incident electric field incident on the point Q, k is the wave number of the radio wave, Z ₀ is the characteristic impedance of the space, and α ₁ is the side formed by the planes 1 and 2 and the unit vector _{1 in FIG.} It is the angle formed by. The equivalent current source I ₂ and the equivalent magnetic current source M ₂ related to the unit vector ₂ related to the surface 2 in FIG. 9 (a) are similarly obtained by the following equations. (Step S8) However, Note that β ₂ , ▲ φ ^′ ₂ ▼, φ in the equations (8) to (10)
₂ , ▲ ^′ ₂ ▼, ₂ , ▲ ^′ ₂ ▼, ₂ , α ₂ are the 9th
Β ₁ , ▲ φ ^′ ₁ ▼, φ ₁ , ▲ shown in FIGS.
^{It corresponds to ′} ₁ ▼, ₁ , ▲ ^′ ₁ ▼, ₁ , α ₁ . Similar calculation is performed for all the edges obtained by the edge search means (7).

Next, the diffracted wave calculation means (10) will be described. As described above, the diffracted wave ₁ radiated in the observation direction from the equivalent electromagnetic flow source temporarily provided on one side is obtained by integrating along that side, and is given by the following equation.

Here, R indicates the distance from the point on the side to the observation point. The same calculation is performed for all the edges obtained by the edge searching means (7) to obtain ₂ , ₃ , ..., _N (N is the total number of edges). (Step S9) Next, the scattering cross section calculating means (11) will be described. Using ₁ , ₂ , ₃ , ..., _N obtained as described above, the scattering cross section σ is obtained by the following equation. (Step S1
0) As described above, in the polyhedron approximation means, the intervals of division are rough where the shape change of the aircraft is small and fine where it is large, and the incident radio waves are distributed on the circumference of the cross section of each individual when the aircraft is divided by virtual lines. Determine points at intervals of about the wavelength, connect the points set for each individual with a straight line, and form a plurality of triangles for each target surface divided into each individual with the above virtual line to form multiple triangles on the target surface. Since the target is approximated to a polyhedron by forming a triangle of, there is an effect that even a target having a complicated shape can be approximated by a polyhedron without twisting with necessary and sufficient accuracy.

Further, the polyhedral approximation means approximates the target with a polyhedron, the side search means searches all the sides of this polyhedron that are visible from the incident direction, and the equivalent wave source calculation means has the unit vector direction obtained by the unit vector calculation means. A line electromagnetic flow source is temporarily installed on all visible sides, the diffracted wave calculation means finds the radiation field from these equivalent line electromagnetic flow sources, and the scattering cross section calculation means calculates the sum of these to determine the scattering interruption. Since the area is calculated, it is not necessary to search the ray trajectory, and the radiation field from the equivalent line electromagnetic flow source can be analytically calculated, so that the scattering cross section of the target in the arbitrary observation direction can be calculated accurately in a short calculation time. effective. Since the side searching means searches the sides of the polyhedron that are visible from the incident direction and temporarily installs an equivalent line electromagnetic flow source on those sides, the scattering cross section can be calculated without diverging.

Note that, in the above description, the case where the target is approximated by a polyhedron whose unit is a triangle is shown, but it may be approximated by a polyhedron whose unit is a polygon such as a quadrangle, or a combination of prisms and pyramids. The scattering cross section can be calculated in the same manner as above.

Further, in the above description, the case where the scattering cross section of an arbitrary observation direction in which the incident direction of the radio wave to the target and the observation direction are different has been described, but the so-called radar disconnection in which the incident direction and the observation direction are the same. The same applies to the calculation of the area, which is calculated as =-'in the above description.

By the way, although an aircraft has been described in the above description, it goes without saying that it can be applied to various objects such as a ship and a car.

The scattering cross-section calculation device described above is used for calculating the scattering cross-sections of radar devices, for example, in order to have the scattering cross-sections of existing aircraft, ships, cars, etc. of known shapes as a database. In the device, the target is easily recognizable by comparing the scattered cross section of the target received by the radar with this database.

[Effect of the Invention] In the scattering cross-section calculation apparatus according to claim 1, a virtual line that divides the target into a plurality of individuals is set on the surface of the target, and each individual when the target is divided by the virtual line Points are set at approximately the wavelength intervals of the radio waves used on the circumference of the cross section, the points set for each individual are connected by a straight line, and a plurality of triangles are divided for each target surface divided by each virtual line above. To form a plurality of triangles on the surface of the target, and is equipped with polyhedral approximation means for approximating the target with a polyhedron, it is possible to approximate a target with a complicated shape with sufficient accuracy without twisting, The scattering cross section can be calculated accurately with a short calculation time.

Further, in the scattering cross-section area calculating device according to claim 2, the target is approximated by a polyhedron, all sides visible from the incident direction of the polyhedron are searched, and equivalent line electromagnetic current sources are provisionally provided on all the visible sides, Since the sum of the radiation fields from these equivalent line electromagnetic sources is calculated, there is no need to search for ray trajectories, and since the radiation field from the equivalent line electromagnetic sources can be calculated analytically, the target field can be calculated in a short calculation time. The scattering cross section in any observation direction can be calculated accurately without diverging.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a scattering cross section calculating apparatus of the present invention, FIG. 2 is a flow chart for explaining the operation of the scattering cross section calculating apparatus, and FIG. 3 is an operation of the scattering cross section calculating apparatus. FIG. 4 is a diagram illustrating an example of an aircraft, FIG. 4 is a diagram illustrating setting of a virtual line that divides the aircraft into a plurality of solids, and FIG. 5 is a case where the aircraft is divided by a virtual line. Of FIG. 6 is a diagram for explaining the determination of points at intervals around the wavelength of the incident radio wave on the circumference of the cross section of each individual, and FIG. 6 is a diagram in which each point shown in FIG. FIG. 7 is an explanatory view of the edge search means (7), FIG. 8 is an explanatory view of the unit vector operation means (8), and FIG. 9 is an equivalent wave source operation means (9). Fig. 10 is a diagram for explaining how to find an equivalent wave source that should be temporarily installed on the side of Is a block diagram showing an example of a scattering cross section computing device. In the figure, (1) is a scattering cross section calculation device, (2) is a shape approximation means, (3) is a ray trajectory search means, (4) is a diffracted wave calculation means, (5) is a scattering cross section calculation means, ( 6) is polyhedral approximation means, (7) is edge search means, (8) is unit vector calculation means, (9) is equivalent wave source calculation means, (10) is diffracted wave calculation means, and (11) is scattering cross section calculation. It is a means. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A scattering cross-section calculating apparatus for calculating a scattering cross-section of a target, wherein a virtual line dividing the target into a plurality of individuals is set on the surface of the target, and the target is divided by the virtual line. Set points at the approximate wavelength intervals of the radio waves used on the circumference of the cross section of each individual of
Connect the points set for each individual with a straight line, form a plurality of triangles on the surface of the target that is divided into each individual with the above virtual line and form a plurality of triangles on the surface of the target, and make the target a polyhedron With a polyhedron approximating means, a side searching means for searching all sides visible from the incident direction of the polyhedron approximated by the polyhedron approximating means, and two sides sharing this side among the sides searched by the side searching means. A unit vector calculation means for obtaining a unit vector whose angle formed by the incident direction and the angle formed by the observation direction that are present in each surface are equivalent to the unit vector calculation means that should be provisionally provided on each side. Equivalent wave source calculation means for obtaining a wave source, diffracted wave operation means for obtaining a diffracted wave emitted from this equivalent wave source in the observation direction, and scattering cross section area for obtaining a scattering cross section from the sum of these diffracted waves Scattering cross section arithmetic apparatus characterized by comprising a means. 2. A scattering cross-section calculation for calculating the scattering cross-section of the target when the incident direction of a radio wave arriving from a sufficiently distant point to the target is different from the observation direction of an observing point sufficiently distant from the target. In the device, a polyhedron approximation means for approximating the target with a polyhedron, a side search means for searching all sides visible from the incident direction of the polyhedron approximated by the polyhedron approximation means, and each side searched by the side search means , Unit vector calculation means for obtaining a unit vector having the same angle with the incident direction and the angle with the observation direction existing in each of the two surfaces sharing this side, and the unit vector calculation means to be provisionally provided on each side. Equivalent wave source calculation means for obtaining an equivalent wave source having a unit vector direction, diffracted wave operation means for obtaining a diffracted wave emitted from the equivalent wave source in the observation direction, and this diffracted wave Scattering cross section arithmetic apparatus characterized by comprising a scattering cross section calculating means for calculating a scattering cross section from the sum.