The effect of free electron density on plasma stealth Zhan Kangsheng Hu Ping2, Liu Shaobin3 (School of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006, Guangdong, China; 2 School of Mathematics and Physics, Nanchang University, Nanchang 330029, Jiangxi; 3 Nanchang University, Nanchang 330029, Jiangxi) When distributed, the attenuation of radar electromagnetic waves in different frequency bands. The study found that the free electron density of the plasma should be related to the radar frequency. When the radar works in low frequency bands such as high frequency and very high frequency, the effect of plasma stealth is not ideal; when the radar works in high frequency bands such as L, S, C, X, etc., the plasma stealth effect is remarkable. In addition, we found that for different radar frequencies, the plasma has an optimal collision frequency to maximize the attenuation of incident electromagnetic waves, which is close to the frequency of incident electromagnetic waves. Plasma stealth technology is a new stealth technology with the advantages of high frequency bandwidth, high efficiency, easy to use, low impact on aircraft, low price and so on. It is receiving widespread attention from various military powers in the world and becomes a popular research topic. The effective conditions for the WKB solution are: from equation (5), when m = 0.5, the plasma electron density is linearly distributed; when m 1.2 plasma The absorption of electromagnetic waves in the sheet is cold, non-magnetized, and the dielectric constant of the collision plasma is obvious. This condition requires that the wave number of the electromagnetic wave changes little within a wavelength range. Unless the density of the plasma changes very much or the frequency of the electromagnetic wave is extremely low, this condition is easy to achieve. At 0, it is perpendicularly incident into the plasma and reflected back at Z = Z0, and then absorbed again by the plasma. When the electromagnetic wave propagates to z = 0 again, its energy is: In equation (16), P. is the electromagnetic wave incidence The energy at z = 0. The two-way attenuation of electromagnetic waves is: (7), Y is the collision frequency of electrons and neutral gas. Obviously, in this case, the electromagnetic wave propagation vector k is in the complex equation (8), k0 = C0 / c is the wave number in vacuum; r and ki are the real and imaginary parts, respectively. When the frequency of incident electromagnetic waves is greater than the plasma frequency, the operating frequency range of UHF radar waves is 300MHz ~ 1GHz. Therefore, the maximum plasma frequency of stealth plasma is 300MHz. The corresponding maximum value of the plasma free electron density It is 1.12X1Cfan3. The free-electron density parabolic distribution and other high-frequency, very high-frequency electromagnetic waves double-pass attenuation L-band radar wave operating frequency range is 1 ~ 2GHz. Therefore, the maximum plasma frequency of stealth plasma is taken as 1GHz. The maximum value of the free electron density of the plasma is 1.24X 1010cm3. When the free electron density is parabolic (m = the ion body ’s two-way attenuation of the electromagnetic wave of the L-band radar incident perpendicularly, the calculation result is as shown. When calculating, the plasma is taken as 30cm thick, the collision frequency of the plasma ranges from 0 to 100GHz, the radar wave frequency is 1, 1.15, 1. The operating frequency range of the C-band radar wave is 4 to 8GHz, and the maximum plasma frequency is 4GHz . The corresponding maximum value of the plasma free electron density is 1.99 × 1011 3. When the parabola distribution of free electron density is given, the plasma The results of C-band radars emitted electromagnetic two-way attenuation. When calculating, the plasma is 30n thick. The collision frequency of the plasma ranges from 0 to 1000 GHz, and the radar wave frequencies are 4.0, 4.6, 5.2, 5.8, 6.4, 7.0, and 7.60, respectively. The calculation result of Cheng attenuation is shown as below. In the calculation, the plasma is 30cm thick, and the collision frequency of the plasma is 0. The operating frequency range of the radar wave in the S band is 2 ~ The large plasma frequency is 2GHz, which corresponds to the maximum plasma free electron density. The value is 4.98X1010cm3. It is the calculation result of the two-way attenuation of the electromagnetic wave of the S-band radar that is perpendicularly incident by the plasma when the free electron density is parabolic. When calculating, the plasma is 30 cm thick. The collision frequency of the plasma ranges from 0 to 1000 GHz, the frequency of the radar wave is 2.0, and the two-way attenuation of the electromagnetic wave of the free electron density parabola to the S-band radar electromagnetic wave. The operating frequency range of the X-band radar wave is 8 to The maximum plasma frequency is taken as 8GHz, and the corresponding maximum value of the plasma free electron density is 7.96 parent 10 "3. When the free electron density parabola distribution is given, the two-way attenuation of the plasma to the perpendicularly incident X-band radar electromagnetic wave Calculation results. In the calculation, the plasma is 30cm thick. The collision frequency of the plasma is in the range of 0. 3 Conclusion In this paper, the parabolic distribution of the free electron density of the plasma (m = l / 4) is taken as an example to calculate the plasma Attenuation of radar electromagnetic waves in different frequency bands. The results show that when the radar works in low frequency bands such as high frequency and very high frequency, the effect of plasma stealth is not ideal; Body stealth effect is remarkable. In addition, the plasma collision frequency also has a greater impact on the ability of the plasma to absorb radar electromagnetic waves. ~ Shows that there is an optimal value of the plasma collision frequency, which is close to the frequency of the incident electromagnetic wave. When the plasma has this collision frequency, the attenuation rate is maximized, and when the frequency of incident electromagnetic waves is increased, the optimum value is also increased. Therefore, properly selecting the collision frequency of the plasma can make the plasma stealth more effective. Of course, the electron collision frequency is also related to the two-way attenuation of the electromagnetic wave of the X-band radar by the molecular density, free electron density, etc. 16. 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