A radiation enhancement method based on non-uniform plasma

Abstract

The present invention relates to a method for radiation enhancement based on non-uniform plasma. This method aims to overcome the relatively simple physical models of existing plasma enhancement technologies and the lack of general discussion on how to achieve optimal enhancement using non-uniform plasma. The method is based on a plasma-enhanced small electric antenna, which includes a spherical plasma shroud and a small electric antenna located within the shroud. Furthermore, the plasma within the shroud is non-uniformly distributed along the radius of the shroud. The radiation enhancement method is as follows: the plasma density and the size of the plasma shroud are adjusted to meet the following conditions, thereby enhancing the radiation of the small electric antenna with the non-uniform plasma.

Description

Technical Field

[0001] The present invention relates to plasma enhanced methods. Background Art

[0002] In recent years, low-temperature gas discharge plasmas have attracted increasing attention in the field of electromagnetic wave regulation. This is because plasma can be regarded as a special electromagnetic metamaterial. On the one hand, the dielectric constant (epsilon) of plasma can be adjusted in a broadband, continuous, and dynamic manner by adjusting external parameters such as discharge power, gas pressure, and discharge gas type. In particular, for weak collision plasmas (the collision frequency is much lower than the electromagnetic wave frequency), the dielectric constant of plasma can be flexibly switched between ENG (epsilon-negative), ENZ (epsilon-near-zero), and ELP (epsilon-low-positive) states. On the other hand, under subwavelength conditions, plasmas exhibit electromagnetic properties that are completely different from those in conventional conditions. The above characteristics make plasmas show great application potential in the design of dynamically adjustable, reconfigurable, and multifunctional microwave electromagnetic devices.

[0003] On the other hand, the development direction of modern antennas is miniaturization, lightweight, ultra-wideband, high gain, adjustable beamwidth (wide scanning), and full polarization. Ultra-wideband is relatively easy to achieve, while the technical core of the remaining characteristics lies in gain. However, miniaturization and high gain are absolutely contradictory. The current common approach in the antenna field is to compromise this contradiction, that is, to obtain relatively high gain by increasing the antenna volume. The subwavelength plasma-enhanced microwave electromagnetic radiation technology developed in recent years provides a new approach to resolving this contradiction. Specifically, the introduction of plasma makes the improvement of passive antenna gain a relatively independent and modular method that does not consider other antenna parameters. The significance of this method lies in: it does not rely too much on the antenna structure and is an active method. Therefore, like active circuits, plasma enhancement methods can effectively decouple the contradiction between miniaturization and high gain.

[0004] Regarding the plasma enhancement phenomenon, in 1967, Messiaen et al. first observed in an experiment that a thin layer of spherical plasma in mercury discharge has an enhancing effect on the electromagnetic radiation of a spherical antenna operating at 300 MHz. In 1968, Chen and Lin also found that within a certain range where the plasma frequency is greater than the electromagnetic wave frequency, the radiation gain of the electric small antenna can reach more than 20 dB. From 2017 to 2018, Kong Fanrong et al. designed an experiment to achieve the enhanced modulation of the transmission and reception of ~1 GHz electromagnetic waves by subwavelength dense plasma (gain ~10 dB). In 2019, Laquerbe et al. discovered through experiments that after the plasma is loaded on the electric small antenna, at a certain operating frequency (250 MHz to 450 MHz) and discharge power, the electric small antenna can achieve good impedance matching with the transmission line and obtain a radiation gain of about 20 dB. Regarding the enhancement mechanism, Bichuskaya, Stuart, Ziolkowski, Gao, Pfeiffer, Wang, Li, Laquerbe, and Laffont et al. have provided explanations from the perspectives of impedance matching, phase modulation, plasmons, and simple harmonic oscillator models. However, most of them used the uniform plasma approximation model for analysis. Regarding the non-uniform plasma enhancement effect, in 1973, Hizal studied the enhancement effect of plasma with a cosine decreasing distribution from the inside to the outside on antenna radiation, and found that the enhancement effect of non-uniform plasma containing a sheath is better than that of uniform plasma tightly covering the antenna. In 2018, Kong et al. studied the enhancement effect of plasma density distribution with decreasing and increasing distribution from the inside to the outside on the radiation of electrically small antennas, and found that the decreasing distribution is more conducive to improving the radiation gain. However, in the models of Hizal and Kong et al., the minimum value of the plasma density is 0. At this time, plasma resonance may occur near the position where the local plasma frequency is approximately equal to the electromagnetic wave frequency. The existence of plasma resonance will seriously weaken the radiation enhancement effect of plasma on electrically small antennas. Furthermore, Hizal and Kong et al. do not provide a general discussion on how to achieve optimal enhancement under non-uniform conditions.

[0005] In addition to research on the plasma enhancement effect in the literature, related patents have also reported on this phenomenon. For example, patent application number CN201610389875.4 discloses a "magnetic dipole antenna based on plasma dielectric modulation," which utilizes the negative dielectric constant of plasma to enhance the antenna's radiation capability by creating an electric field resonance within the magnetic dipole antenna. Patent application number CN201610356451 discloses a "device for enhancing the electromagnetic radiation of a miniaturized omnidirectional antenna using plasma modulation," which solves the problem of traditional metal conductor antennas being unable to simultaneously achieve high gain and miniaturization, while also reducing the antenna's size and radar cross-section. Patent application number CN202010093055.7 discloses a "tunable, high-resolution, multi-band enhanced plasma generating device," which can simultaneously enhance the intensity of multiple transmitted signals or extract and enhance electromagnetic signals of multiple target frequencies from a complex background electromagnetic field. Patent application number CN201910678454.7 discloses a "signal-enhanced plasma stealth antenna window", which, through the synergy of the inner and outer plasma layers, can achieve selective stealth and enhancement of electromagnetic waves in different target bands in the same system. Patent application number CN202110625957.5 discloses "an enhanced electric small antenna with stealth function". This patent adopts the method of staggered excitation of the inner and outer plasma layers to achieve the synergistic effect of stealth and enhancement effects under different combinations of communication waves and detection waves in a wider frequency band. However, the above patents do not generally discuss how to achieve effective enhancement through non-uniform plasma.

[0006] In summary, the current research on plasma enhanced technology still has the following problems:

[0007] (1) Existing theoretical and numerical simulation studies on subwavelength plasma-enhanced microwave electromagnetic radiation mostly focus on an ideal uniform plasma distribution, and existing patents on plasma enhancement phenomena also mainly adopt a uniform plasma distribution. However, actual plasmas usually have certain non-uniformities.

[0008] (2) In existing studies of inhomogeneous plasmas, the minimum plasma density is usually taken as 0. In this case, electromagnetic waves are likely to excite plasma resonance in the plasma. Since plasma resonance is usually accompanied by strong energy absorption, the emergence of resonance effects will seriously weaken the radiation enhancement effect of the plasma on the small antenna.

[0009] In general, a general design method for achieving optimal enhancement using inhomogeneous plasmas is currently lacking. Summary of the Invention

[0010] The purpose of the present invention is to overcome the relatively simple physical model of existing plasma enhancement technology and the lack of general discussion on how to achieve optimal enhancement using non-uniform plasma, and to provide a radiation enhancement method based on non-uniform plasma.

[0011] The present invention provides a radiation enhancement method based on non-uniform plasma. The method is implemented based on a plasma-enhanced small electric antenna. The plasma-enhanced small electric antenna includes a spherical shell plasma cover and a small electric antenna located inside the plasma cover. In addition, the plasma inside the plasma cover is non-uniformly distributed along the radius of the plasma cover.

[0012] Radiation enhancement methods are as follows:

[0013] The plasma density and the size of the plasma shield are adjusted to meet the following conditions, so that the radiation of the non-uniform plasma to the small electric antenna is enhanced: the size includes the inner diameter and the outer diameter;

[0014]

[0015] n c =ω 2 ε0m e / e 2

[0016]

[0017] n pin / n c >1

[0018] n pout / n c >1

[0019]

[0020] 0.05<r out / λ<0.1

[0021] Among them, ω p0 represents the plasma frequency in the plasma shield corresponding to the optimal enhancement condition of uniform plasma, n0 represents the plasma density corresponding to the optimal enhancement condition of uniform plasma, and n c represents the critical plasma density, ε0 ​​represents the dielectric constant in vacuum, m e is the mass of the electron, e represents the elementary charge, n p (r) represents the distribution function of plasma density along the radius of the plasma shield, r represents the distance from a point in the plasma shield to the center of the plasma shield, n pin and n pout are the plasma densities at the inner and outer boundaries of the plasma shield, r in and rout They represent the inner and outer diameters of the plasma shield respectively, and λ represents the wavelength of the electromagnetic wave radiated by the electric small antenna in vacuum.

[0022] The beneficial effects of the present invention are:

[0023] The present invention proposes a general design method for achieving non-uniform plasma enhancement. By optimizing the plasma density distribution, the plasma resonance caused by electromagnetic waves inside the plasma is avoided, thereby achieving a relatively ideal enhancement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the cross-sectional structure of the plasma enhanced electric small antenna in the xz plane;

[0025] Figure 2 is the variation characteristics of the modulus of the first-order Mie scattering factor with the normalized plasma frequency when the plasma is uniformly distributed in the plasma shield;

[0026] Figure 3 is the plasma density distribution curve along the r direction when the plasma density decreases linearly from the inside to the outside in the present invention;

[0027] Figure 4 is the plasma density distribution curve along the r direction when the plasma density is distributed parabolically decreasing from the inside to the outside in the present invention;

[0028] Figure 5 It is the plasma density distribution curve along the r direction when the plasma density decreases exponentially from the inside to the outside in the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0032] Specific embodiment 1: This embodiment provides a radiation enhancement method based on non-uniform plasma. The method is implemented based on a plasma-enhanced small electric antenna. The plasma-enhanced small electric antenna includes a spherical shell plasma cover and a small electric antenna located within the plasma cover. In addition, the plasma within the plasma cover is non-uniformly distributed along the radius of the plasma cover.

[0033] Radiation enhancement methods are as follows:

[0034] The plasma density and the size of the plasma shield are adjusted to meet the following conditions, so that the radiation of the non-uniform plasma to the small electric antenna is enhanced: the size includes the inner diameter and the outer diameter;

[0035]

[0036] n c =ω 2 ε0m e / e 2

[0037]

[0038] n pin / n c >1

[0039] n pout / n c >1

[0040]

[0041] 0.05<r out / λ<0.1

[0042] Among them, ω p0 represents the plasma frequency in the plasma shield corresponding to the optimal enhancement condition of uniform plasma, n0 represents the plasma density corresponding to the optimal enhancement condition of uniform plasma, and n c represents the critical plasma density, ε0 ​​represents the dielectric constant in vacuum, m e is the mass of the electron, e represents the elementary charge, n p (r) represents the distribution function of plasma density along the radius of the plasma shield, r represents the distance from a point in the plasma shield to the center of the plasma shield, n pin and n pout are the plasma densities at the inner and outer boundaries of the plasma shield, r in and r out They represent the inner and outer diameters of the plasma shield respectively, and λ represents the wavelength of the electromagnetic wave radiated by the electric small antenna in vacuum. Specific implementation method 2

[0044] This embodiment is a further explanation of the first embodiment. In this embodiment, the plasma density decreases linearly from the inside to the outside along the radius of the plasma shield. p (r) is,

[0045]

[0046] The other technical solutions of this embodiment are the same as those of the first embodiment. Specific implementation method three

[0048] This embodiment is a further explanation of the first embodiment. In this embodiment, the plasma density decreases linearly from the inside to the outside along the radius of the plasma shield. p (r) is,

[0049]

[0050] The other technical solutions of this embodiment are the same as those of the first embodiment. Specific implementation method four

[0052] This embodiment is a further explanation of the first embodiment. In this embodiment, the plasma density decreases exponentially from the inside along the radius of the plasma shield. p (r) is,

[0053] n p (r)=4(n pin -n pout )2 -r +2n pout -n pin .

[0054] The other technical solutions of this embodiment are the same as those of the first embodiment. Specific implementation method five

[0056] This embodiment is a further explanation of one of the embodiments 1 to 4. In this embodiment, the plasma frequency ω in the plasma hood corresponding to the optimal enhancement condition for uniform plasma is obtained. p0 The steps are as follows:

[0057] Step 1: Assuming that the plasma in the plasma shield is uniformly distributed, the first-order Mie scattering factor of the plasma shield is

[0058]

[0059] in,

[0060]

[0061]

[0062] x=kr in

[0063] y=kr out

[0064] ψ1(z)=zj1(z)

[0065] χ1(z)=-zy1(z)

[0066] ξ1(z)=z[j1(z)+iy1(z)]

[0067] where ψ'1(z), χ'1(z), and ξ'1(z) are the first-order derivatives of ψ1(z), χ1(z), and ξ1(z), respectively; v represents the collision frequency of the plasma; ω represents the angular frequency of the electromagnetic wave radiated by the electric small antenna; i represents the imaginary unit; k represents the wave number of the electromagnetic wave radiated by the electric small antenna; and m p represents the refractive index of the plasma, ω p represents the plasma frequency, j1(z) and y1(z) represent the first-order spherical Bessel functions of the first and second kinds, respectively, and z represents the independent variable of the corresponding function;

[0068] Step 2: By solving the maximum value of the a1 modulus, the plasma frequency ω under the optimal enhancement condition can be obtained. p0 .

[0069] The other technical solutions of this embodiment are the same as those of any one of the first to fourth embodiments. Specific implementation method six

[0071] This embodiment is a further explanation of the fifth embodiment. In this embodiment, the plasma in the spherical plasma shield is a weak collision plasma, which satisfies

[0072] v / ω<0.1.

[0073] The other technical solutions of this embodiment are the same as those of the fifth embodiment. Specific embodiment seven

[0075] This embodiment is a further explanation of the sixth embodiment. In this embodiment, the collision frequency v of the plasma is 0.1 GHz.

[0076] The other technical solutions of this embodiment are the same as those of embodiment 6. Specific embodiment eight

[0078] This embodiment is a further explanation of one of the first to fourth embodiments. In this embodiment, a gap is provided between the plasma shield and the small electric antenna in the plasma enhanced electric antenna.

[0079] The other technical solutions of this embodiment are the same as those of any one of the first to fourth embodiments. Specific embodiment nine

[0081] This embodiment is a further explanation of the seventh embodiment. In this embodiment, the small electric antenna is eccentrically disposed relative to the plasma shield.

[0082] The other technical solutions of this embodiment are the same as those of embodiment seven. Specific embodiment 10

[0084] This embodiment is a further explanation of the seventh embodiment. In this embodiment, the small electric antenna is a spherical dipole antenna, which is concentrically arranged in the hollow area of ​​the plasma shield;

[0085] The operating frequency of the electric small antenna is 1 GHz; the electromagnetic wave radiated by the electric small antenna is polarized along the z direction and propagates in the x direction.

[0086] The other technical solutions of this embodiment are the same as those of embodiment seven. Specific embodiments

[0088] The purpose of the present invention is to provide a method for non-uniform plasma size and density distribution that can overcome plasma resonance attenuation and achieve high gain, in order to solve the problem of non-uniform plasma enhancing the radiation efficiency of small electric antennas from a practical point of view.

[0089] like Figure 1 As shown, the plasma enhanced electric small antenna comprises a spherical shell plasma cover 1 and an electric small antenna system 2;

[0090] The inner and outer diameters of the spherical shell plasma shield 1 are r in and r out ;

[0091] The electric small antenna system 2 is located in the spherical shell plasma shield, eccentrically or concentrically placed, meeting the requirements of

[0092] r a <r in , (1)

[0093] Among them, r a The radius of the smallest sphere that can accommodate an electrically small antenna system.

[0094] There is a gap between the plasma shield and the antenna system;

[0095] The plasma in the spherical shell plasma shield is a weak collision plasma, which satisfies

[0096] v / ω<0.1, (2)

[0097] Where v is the collision frequency of the plasma, and ω represents the angular frequency of the electromagnetic wave radiated by the electric small antenna.

[0098] When the plasma hood is open, the plasma parameters inside the plasma hood are obtained through the following two steps:

[0099] In the first step, assuming that the plasma in the plasma shroud is uniformly distributed, the first-order Electron-Mie scattering factor of the plasma spherical shell is

[0100]

[0101] in,

[0102]

[0103]

[0104] x=kr in , (6)

[0105] y=kr out , (7)

[0106] ψ1(z)=zj1(z), (8)

[0107] χ1(z)=-zy1(z), (9)

[0108]

[0109] Among them, k is the wave number of electromagnetic waves radiated by the small antenna; m p represents the refractive index of plasma; ω p represents the plasma frequency; j1(z) and y1(z) represent the first-order spherical Bessel functions of the first and second kinds, respectively; z represents the independent variable of the corresponding function; and i represents the imaginary unit. is a spherical Hankel function of the first kind.

[0110] By solving the maximum value of the a1 mode value, the plasma frequency ω under the optimal enhancement condition can be obtained. p0 ,Right now

[0111] max|a1|→ω p0 , (11)

[0112] The second step is to satisfy the size and density distribution of the non-uniform plasma on the basis of uniform plasma.

[0113]

[0114] n c =ω 2 ε0m e / e2 , (13)

[0115]

[0116] n pin / n c >1, (15)

[0117] n pout / n c >1, (16)

[0118]

[0119] 0.05<r out / λ<0.1, (18)

[0120] Among them, ω p0 represents the plasma frequency in the plasma shield corresponding to the optimal enhancement condition of uniform plasma; n0 represents the plasma density corresponding to the optimal enhancement condition of uniform plasma, that is, the plasma density corresponding to the optimal enhancement condition under uniform plasma distribution; n c It represents the plasma density corresponding to the time when the plasma frequency is equal to the electromagnetic wave frequency, that is, the critical plasma density; ε0 represents the dielectric constant in vacuum, m e is the mass of the electron, e represents the elementary charge, n p (r) represents the distribution function of plasma density along the radius of the plasma shield, r represents the distance from a point in the plasma shield to the center of the plasma shield, n pin and n pout are the plasma densities at the inner and outer boundaries of the plasma shield, r in and r out They represent the inner and outer diameters of the plasma shield respectively, and λ represents the wavelength of the electromagnetic wave radiated by the electric small antenna in vacuum.

[0121] The inner diameter r of the spherical shell plasma shield 1 in =1cm, outer diameter r out =2cm;

[0122] The electric small antenna system 2 is a spherical dipole antenna, which is concentrically placed in the hollow area of ​​the plasma shield, where r a =0.2cm, feeding voltage is 1V;

[0123] The enhancement effect of inhomogeneous plasma on the radiation of small electric antennas is studied by numerical simulation. The collision frequency of the plasma is 0.1 GHz and the operating frequency of the small electric antenna is 1 GHz (the electromagnetic wave is polarized in the z direction and propagates in the x direction).

[0124] Under the above conditions, the following three cases of uneven distribution of plasma density are taken as examples:

[0125] 1. When the plasma density decreases linearly from the inside to the outside, the plasma density distribution along the r direction is as follows: Figure 3 shown.

[0126] Different normalized plasma frequencies (ω pe The variation characteristics of the first-order Mie scattering factor amplitude |a1| of the uniform plasma spherical shell under the condition of / ω) are as follows: Figure 2 As shown. It can be seen that when |a1| reaches the maximum value, the plasma frequency ω p0 =2.069×2πrad / s, and the corresponding plasma density is n0=5.3096×10 16 m -3 Based on formula (14), assume that the plasma density decreases linearly from the inside to the outside, that is,

[0127]

[0128] Then the relationship between the plasma density at the inner and outer boundaries of the plasma shield can be obtained from formula (17):

[0129] 11n pin +17n pout =28n0 (20)

[0130] Considering formulas (15) and (16), let n pin =8×10 16 m -3 , then from formula (20) we can get n pout =3.5688×10 16 m -3 Furthermore, by substituting the above parameters into COMSOL software simulation, the radiation gain of the electrically small antenna is obtained to be 25.6894dB.

[0131] 2. When the plasma density decreases parabolically from inside to outside, the plasma density distribution along the r direction is as follows: Figure 4 shown.

[0132] Different normalized plasma frequencies (ω pe The variation characteristics of the first-order Mie scattering factor amplitude |a1| of the uniform plasma spherical shell under the condition of / ω) are as follows: Figure 2 As shown. It can be seen that when |a1| reaches the maximum value, the plasma frequency ω p0 =2.069×2πrad / s, and the corresponding plasma density is n0=5.3096×10 16 m-3 Based on formula (14), the plasma density is assumed to be parabola decreasing from the inside to the outside, that is,

[0133]

[0134] Then the relationship between the plasma density at the inner and outer boundaries of the plasma shield can be obtained from formula (17):

[0135] 39n pin +31n pout =70n0 (22)

[0136] Considering formulas (15) and (16), let n pin =8×10 16 m -3 , then from formula (22) we can get n pout =1.9249×10 16 m -3 Furthermore, by substituting the above parameters into COMSOL software simulation, the radiation gain of the electrically small antenna is obtained to be 23.7973dB.

[0137] 3. When the plasma density decreases exponentially from the inside to the outside, the plasma density distribution along the r direction is as follows: Figure 5 shown.

[0138] Different normalized plasma frequencies (ω pe The variation characteristics of the first-order Mie scattering factor amplitude |a1| of the uniform plasma spherical shell under the condition of / ω) are as follows: Figure 2 As shown. It can be seen that when |a1| reaches the maximum value, the plasma frequency ω p0 =2.069×2πrad / s, and the corresponding plasma density is n0=5.3096×10 16 m -3 Based on formula (14), assume that the plasma density decreases exponentially from the inside to the outside, that is,

[0139] n p (r)=4(n pin -n pout )2 -r +2n pout -n pin (twenty three)

[0140] Then the relationship between the plasma density at the inner and outer boundaries of the plasma shield can be obtained from formula (17):

[0141]

[0142] Considering formulas (15) and (16), let n pin=8×10 16 m -3 , then from formula (24) we can get n pout =3.9408×10 16 m -3 Furthermore, by substituting the above parameters into COMSOL software simulation, the radiation gain of the electrically small antenna is obtained to be 24.7247dB.

[0143] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other embodiments.

Claims

1. A radiation enhancement method based on non-uniform plasma, characterized in that: The method is implemented based on a plasma-enhanced electric small antenna, which includes a spherical shell plasma cover and an electric small antenna located in the plasma cover; and the plasma in the plasma cover is non-uniformly distributed along the radius of the plasma cover; The radiation enhancement method is as follows: The plasma density and the size of the plasma shield are adjusted to meet the following conditions, so that the radiation of the non-uniform plasma to the small electric antenna is enhanced: the size includes the inner diameter and the outer diameter; n c =ω 2 e0m e / e 2 n pin / n c >1 n pout / n c >1 0.05<r out / λ<0.1 Among them, ω p0 represents the plasma frequency in the plasma shield corresponding to the optimal enhancement condition of uniform plasma, n0 represents the plasma density corresponding to the optimal enhancement condition of uniform plasma, and n c represents the critical plasma density, ω represents the angular frequency of the electromagnetic wave radiated by the small antenna, ε0 represents the dielectric constant in vacuum, m e is the mass of the electron, e represents the elementary charge, n p (r) represents the distribution function of plasma density along the radius of the plasma shield, r represents the distance from a point in the plasma shield to the center of the plasma shield, n pin and n pout are the plasma densities at the inner and outer boundaries of the plasma shield, r in and r out They represent the inner and outer diameters of the plasma shield respectively, and λ represents the wavelength of the electromagnetic wave radiated by the electric small antenna in vacuum.

2. The radiation enhancement method based on non-uniform plasma according to claim 1, characterized in that: The plasma density decreases linearly from the inside to the outside along the radius of the plasma shield, n p (r) is, 3. The radiation enhancement method based on non-uniform plasma according to claim 1, characterized in that: The plasma density decreases linearly from the inside to the outside along the radius of the plasma shield, n p (r) is, 4. The radiation enhancement method based on non-uniform plasma according to claim 1, characterized in that: The plasma density decreases exponentially from the inside along the radius of the plasma shield, n p (r) is, <h2 style=";text-align:left;direction:ltr">n<h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> (r)=4(n<h2 style=";text-align:left;direction:ltr"> pin <h2 style=";text-align:left;direction:ltr"> -n<h2 style=";text-align:left;direction:ltr"> pout <h2 style=";text-align:left;direction:ltr"> )2<h2 style=";text-align:left;direction:ltr"> -r <h2 style=";text-align:left;direction:ltr"> +2n<h2 style=";text-align:left;direction:ltr"> pout <h2 style=";text-align:left;direction:ltr"> -n<h2 style=";text-align:left;direction:ltr"> pin <h2 style=";text-align:left;direction:ltr"> 。 5. A radiation enhancement method based on non-uniform plasma according to any one of claims 1 to 4, characterized in that: The plasma frequency ω in the plasma shield corresponding to the optimal enhancement condition of uniform plasma is obtained p0 The steps are as follows: Step 1: Assuming that the plasma in the plasma shield is uniformly distributed, the first-order Mie scattering factor of the plasma shield is in, x=kr in y=kr out ψ1(z)=zj1(z) χ1(z)=-zy1(z) ξ1(z)=z[j1(z)+iy1(z)] where ψ′1(z), χ′1(z), and ξ′1(z) are the first-order derivatives of ψ1(z), χ1(z), and ζ1(z), respectively; v represents the collision frequency of the plasma; ω represents the angular frequency of the electromagnetic wave radiated by the electric small antenna; i represents the imaginary unit; k represents the wave number of the electromagnetic wave radiated by the electric small antenna; and m p represents the refractive index of the plasma, ω p represents the plasma frequency, j1(z) and y1(z) represent the first-order spherical Bessel functions of the first and second kinds, respectively, and z represents the independent variable of the corresponding function; Step 2: By solving the maximum value of the a1 modulus, the plasma frequency ω under the optimal enhancement condition can be obtained. p0 .

6. The radiation enhancement method based on non-uniform plasma according to claim 5, characterized in that: The plasma in the spherical plasma shield is a weak collision plasma, which satisfies v / ω<0.

1.

7. The radiation enhancement method based on non-uniform plasma according to claim 6, characterized in that: The collision frequency v of the plasma is 0.1 GHz.

8. A radiation enhancement method based on non-uniform plasma according to any one of claims 1 to 4, characterized in that: There is a gap between the plasma shield and the electric small antenna in the plasma enhanced electric small antenna.

9. The radiation enhancement method based on non-uniform plasma according to claim 7, characterized in that: The electric small antenna is eccentrically arranged relative to the plasma shield.

10. The radiation enhancement method based on non-uniform plasma according to claim 7, characterized in that: The electric small antenna is a spherical dipole antenna, which is concentrically arranged in the hollow area of ​​the plasma shield; The operating frequency of the small electric antenna is 1 GHz; the electromagnetic waves radiated by the small electric antenna are polarized along the z direction and propagate in the x direction.

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