Radar intercept area (Radar cross Section,rcs) (MATLAB part emulation +code)

I. RCS definition

any electromagnetic waves with a definite polarization are exposed to the target, which can cause refraction or scattering in all directions.

The scattering wave is divided into two parts: one is composed of the scattering wave with the same polarization as the receiving antenna, and the two is the different change of the scattering wave, and the receiving antenna is not responding. These two polarization orthogonal, respectively called the Primary polarization (Principle polarization,pp) and the vertical polarization (orthogonal polarization,op). The intensity of the backscattering energy with the same polarization wave as the radar irradiation antenna is used to define the target RCS.

in popular words: PCs is a physical quantity that measures the intensity of the echoes produced by the target under radar waves. It is the imaginary area of the target, which is represented by a projection area of an equal equivalent reflector, and the equivalent reflector has the same echo power as the defined target in the unit stereo angle of the receiving direction. The general symbol σ is used to denote the radar scattering cross section of the target.

Using σ to represent the intercept area of a radar target can be written as:

This is the experimental definition of the cross-sectional area of radar target. σ is a factor in the basic radar equation. Known transmit power PT, transmit and receive antenna gain G, wavelength λ, target to radar distance R, the radar receiving antenna intercepts the power of:

To define the power density of the scattering wave from the receiving antenna, then:

According to the power density formula and the antenna interception power, can be introduced:

                                                                              

In order to ensure that the radar receiving antenna is in the far field (that is, the scattering wave received by the antenna is a plane wave), the modified formula is:

This type is referred to as single base RCS, backscatter RCS or simple target RCS.

--the PR equals the power of Ei, EI indicates the radiated field strength of the radar at the target;

--equal to the power of ER, er indicates the scattering field strength of the target at the receiving antenna .

Because the radar emits spherical waves, the scattering waves at the receiving antenna are approximately expressed as plane wave only when the far-field conditions are satisfied (roughly speaking, when the target distance is sufficiently far away).

"The definition of the intercept area of the radar target is independent of the distance.

The radar cross-sectional area of a target is related to the geometrical size and shape of the target itself, the material, the target angle of view, the radar operating frequency and the polarization of the radar transmitting and receiving antenna.

When other conditions are not changed, the larger the target size, the larger the radar cross-sectional area. For a certain radar frequency and fixed angle of view, the target of the radar cross-sectional area is determined by polarization.

Under the condition of far-field and linear scattering, the relation between cross-sectional area and polarization of radar target can be expressed as matrix, which is called the scattering matrix of radar target.

RCS of some complex targets

There are many practical goals in nature, which are far more complex than the target structure of the general situation. This is because they contain multiple scattering bodies, and the surface shape and dielectric coefficients are extremely complex. For example: insects, birds, airplanes, ships and so on.

The RCS of humans is as follows:

Specific frequency F=9.4ghz under different insect RCS such as:

The general method of reflecting the radar scattering cross section is 10 times times the value of the radar scattering section, the symbol is ΣDBSM, the unit is Decibel square meter (DBSM),

That is σdbsm=10lgσ.

For example, the RCS value of 0.1 square meters corresponds to 10 decibels square meters (i.e. -10DBSM).

Iii. Factors affecting RCS

The RCS of radar is related to the shape, size, structure and material of the target, as well as the frequency, polarization mode and incidence angle of the incident electromagnetic wave.

"The basic types of electromagnetic scattering sources on unmanned aerial vehicles include specular reflection, edge diffraction, apex diffraction, creeping wave diffraction, diffraction of traveling waves, and diffraction caused by electromagnetic mutations in non-slender bodies."

"When the electromagnetic wave is perpendicular to the surface of the local smooth target, a strong scattering echo is generated in the direction of the beam, which is called specular reflection, which is a strong scattering source.

"When the electromagnetic wave is transmitted to the edge of the target, the scattering echo is mainly derived from the diffraction of the incident electromagnetic wave at the target edge, which differs from the reflection in that a beam of incident waves can produce no number of rays around the edge and is an important scattering source.

"For conventional aircraft without stealth measures, its scattering fields include reflection and diffraction fields, mainly mirror reflection and edge diffraction.

"For stealth aircraft, take a variety of measures to make specular reflection and edge diffraction basically disappear.

Iv. RCS Measurement

It is also important to understand RCS projections before doing different RCS calculations, in fact, RCS measurements are challenging and stimulating intelligence, like building a house, accurately predicting the RCS of the target is no exaggeration to be understood as piling. In addition, RCS calculations require cross-cutting techniques and knowledge accumulation. At present, there are two kinds of RCS measurement methods: Exact method and approximate method.

With regard to the exact method and the approximation method, the author will not repeat the one by one, and interested readers should study the details of these methods on their own.

The calibration process in RCS measurement is often measured by contrast method in engineering. The RCS value of the target is σt, the RCS of the known standard body is σc, and the RCS of the target and standard body measured in the experiment is Σtca,σta respectively, (the actual measured is the power value), the RCS of the target can be calculated as:

Σt (true Value) = (Σc/σta) ΣTCA

The backward scattering section is commonly used to represent the scattering energy, or the return strength, of the rear direction in radar observation.

"It is important to note that RCS is a hypothetical area used for engineering applications, and is a measure of the capability of the backscattering power of a target at a certain incident power; the amount is described in area units. The larger the area, the stronger the backscattering capability, and the greater the return power generated.

V, MATLAB simulation observation RCS and the angle of view, frequency, polarization relationship

For intuitive purposes, the author uses Matlab to simulate the diagram and release some source code:

5.1 Relationship with Perspective (interested readers can dig into it)

" Unit parameter: 1 square meters

Radar line of sight starting angle: 0

"Scattering body spacing: 1 m

"Radar angle of view change range: 0-180 degrees

RCS vs. Perspective Relationship:

"Fig1 (scattering body spacing takes 0.25m, Radar frequency takes 80G (arbitrary take, 80G current technology ...) ））

Some experimental data:

  Columns 3554 through 3564    0.5093    0.4887    0.4685    0.4486    0.4291    0.4100    0.3913    0.3730    0.3551    0.3376    0.3205  Columns 3565 through 3575    0.3038    0.2875    0.2717 0.2562    0.2412    0.2267    0.2125    0.1988    0.1855    0.1727  0.1603 Columns 3576 Through 3586    0.1483    0.1368    0.1258    0.1152    0.1051    0.0954 0.0861 0.0774    0.0691    0.0612    0.0539  Columns 3587 through 3597    0.0469    0.0405    0.0345 0.0291    0.0240    0.0195    0.0154    0.0118    0.0087    0.0061  0.0039 Columns 3598 Through 3601    0.0022    0.0010    0.0003    0.0001

"Fig2 (scattering distance above, radar frequency reduced to 8G)

Some experimental data:

 Columns 3532 through 3542 0.1133 0.1101 0.1069 0.1037 0.1007 0.0976 0.0946 0.0917 0.0887 0.0859 0     .0831 Columns 3543 through 3553 0.0803 0.0776 0.0749 0.0723 0.0697 0.0671 0.0646 0.0622 0.0598 0.0574 0.0551 Columns 3554 through 3564 0.0529 0.0507 0.0485 0.0464 0.0443 0.0423 0.0403 0     .0384 0.0365 0.0346 0.0329 Columns 3565 through 3575 0.0311 0.0294 0.0278 0.0262 0.0246 0.0231 0.0216 0.0202 0.0189 0.0176 0.0163 Columns 3576 through 3586 0.0151 0.0139 0.0128 0.0117 0     .0107 0.0097 0.0087 0.0079 0.0070 0.0062 0.0055 Columns 3587 through 3597 0.0048 0.0041 0.0035 0.0030 0.0025 0.0020 0.0016 0.0013 0.0010 0.0007 0.0005 Columns 3598 through 3601 0.0003 0 .0002 0.0001 0.0001 

5.2 Matlab Program (explanation)

EPS = 0.00001;% This is a worthwhile role in my previous blog has been described in detail, here does not repeat the% Enter scatterer spacing, in the meters% in meters%scat_spacing = 1.0;% Pitch initial 1m, Readers can modify the% enter frequency% input frequency%freq = 3.0e+9;% frequency 30Gwavelength = 3.0e+8/freq;% wavelength Formula ha, I can't understand.% Compute aspect angle ve ctor% computing Perspective Vector aspect_degrees = 0.:.05:180.; % range 180, step 0.05aspect_radians = (pi/180). * aspect_degrees;% Everybody think, this is the degree and Radian conversion% Compute electrical scatterer spacing vector in wavelength unitselec_spacing = (2.0 * scat_spacing/wavelength). * cos (aspect_radians);% Compute RCS (RCS = RCS_SCAT1 + rcs_scat2)% SCAT1 is taken as phase refernce POINTRCS = ABS (1.0 + COS ((2.0 * pi). * elec_spacing) ... + i * Sin ((2.0 * pi). * elec_spacing)), RCS = RCS + Eps;rcs = 20.0*LOG10 (RCS); % representation in dbsm% plot RCS versus aspect angle% start drawing Plot (ASPECT_DEGREES,RCS);% Note Parameters Oh, it is estimated that many people directly copy the use, for this hand party, I am. Hey.. grid;% grid Xlabel (' Perspective/'),% studied matlab know Ylabel (' rcs/dbsm ');% ibid.%title (' Frequency is 3GHz; scatterrer spacing is 1.0m ');

5.3 With the frequency, and the polarization is similar, and 5.2, or to leave a suspense, many programs are actually on the Internet, it depends on whether you would like to understand it.
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Radar intercept area (Radar cross Section,rcs) (MATLAB part emulation +code)