Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.     

Parametric study of plasma active medium and gain saturation region in a Ne-like soft X-ray laser

Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm⁻¹ gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium.     

Finite difference time domain analysis of a photonic crystal substrate patch antenna

Planar microstrip patch antennas can achieve a wide range of radiation patterns. However, due to surface-wave losses, they have low bandwidth, low gain, and a potential decrease in radiation efficiency. In order to minimize the surface-wave effects, a photonic-band gap (PBG) substrate is proposed. The PBG structure significantly diminishes the surface-wave modes and thus improves the gain and far-field radiation pattern and efficiency. In this paper, using FDTD, an accurate full-wave analysis of surface-wave propagation in a rectangular microstrip patch antenna with and without PBG is presented. Finally, the antenna fabricated and result of measurement was compared with numerical simulation.     

Theoretical study of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium

The radiation properties of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium are studied. The array factor and far-zone EM-mode and P-mode radiation fields of the array geometry are derived using vector wave function techniques and pattern multiplication approaches. The total field patterns and various characteristics of pattern such as half power beam width (HPBW), first null beam width (FNBW) and direction of maximum radiation are computed for two different values of progressive phase excitation difference between the elements. The results of this array geometry are obtained both in plasma medium and in free space and compared with those of single element equilateral triangular patch microstrip antenna.     

等离子体天线表面电流分布与辐射特性研究

建立了表面波驱动等离子体天线装置,提出了一种等离子体天线表面电流指数分布模型,并利用该表面电流分布模型计算了天线的辐射方向图.研究结果表明,等离子体密度随轴向距离的增大呈指数衰减趋势.正常工作状态下表面波波矢虚部随等离子体密度的增大而下降,遵循与等离子体密度类似的指数衰减规律,但其实部则基本保持不变.等离子体天线的表面电流呈振幅指数衰减行波模式.利用该表面电流分布模型计算得到的辐射方向图呈现典型的8字形分布,与实验测量结果良好符合.当射频功率减小,等离子体天线辐射方向图宽化.     

单源单极等离子体天线辐射特性实验研究

为了对等离子体天线进行更深入的研究,必须结合实验获得其真实辐射特性,为此搭建了天线辐射特性测量平台,对单源单极等离子体天线的辐射特性进行了详细的实验研究。通过测量辐射远场区接收天线感应电压数据,得出了天线的辐射方向图、主旁瓣宽度和方向系数;通过与金属天线的辐射场最大值对比,得出了天线的辐射效率;通过测量输入功率和反射功率得出了天线的输入阻抗。此项工作弥补了在等离子体天线研究中实验研究不足的问题。     

单源单极等离子体天线辐射特性实验研究

为了对等离子体天线进行更深入的研究,必须结合实验获得其真实辐射特性,为此搭建了天线辐射特性测量平台,对单源单极等离子体天线的辐射特性进行了详细的实验研究。通过测量辐射远场区接收天线感应电压数据,得出了天线的辐射方向图、主旁瓣宽度和方向系数;通过与金属天线的辐射场最大值对比,得出了天线的辐射效率;通过测量输入功率和反射功率得出了天线的输入阻抗。此项工作弥补了在等离子体天线研究中实验研究不足的问题。     

磁约束技术对激光诱导等离子体辐射特性的影响

为了提高激光诱导击穿光谱质量,利用Nd：YAG激光器烧蚀土壤样品,研究了磁场作用下的激光诱导等离子体辐射特性。实验结果表明,在相同激光输出能量条件下,随着磁场强度的增大,等离子体的辐射强度逐渐增强。计算可知,当采用的磁场强度为0.5 T时,样品元素Al,Fe,Ba和Ti的光谱线强度比无磁场作用时的分别增强了52.35%,46.64%,64.01%和51.73%,光谱信噪比分别提高了45.44%,69.64%,40.26%和41.33%;而等离子体的电子温度和电子密度分别提高了1 355.01 K和0.531016 cm-3。可见,利用磁场约束等离子体的技术是提高激光光谱质量的一种有效方法。     

Magnetic line source diffraction by a conductive half-plane in an anisotropic plasma

An integral theory that is associated with the scattered fields is considered for the solution of H-polarized line source diffraction by a conductive half-plane, which is surrounded by an anisotropic plasma. As the anisotropy does not affect an E-polarized incident wave, only one polarization case is considered. The cold plasma medium is characterized by the dielectric tensor. The constant external magnetic field producing the anisotropy in a cold plasma is applied parallel to the edge of the half-plane. The total, scattered, and diffracted waves are derived in terms of the Fresnel functions. Therefore, finite magnitude values at the transition boundaries are obtained. The wave behaviours are investigated numerically for different quantities of the medium.     

双负媒质结构改善Ku波段天线辐射特性

基于负介电常数和负磁导率产生原理,采用金属细线和裂环谐振器结构,针对12.5 GHz频率开展双负媒质结构设计。通过特殊边界条件下S参数计算以及Nicolson-Ross-Weir方法,完成等效参数的提取,获得介电常数、磁导率、折射率实部均为负值,且折射率接近于0的左手材料特性。将双负媒质结构加载于Ku波段圆锥喇叭口面进行仿真优化,提高天线增益2.17 dB,在11~13 GHz频带范围内,加载天线的增益均有所改善。实验结果表明,口面加载双负媒质结构后,天线增益提高1.51 dB,后向辐射减小5.7 dB,辐射特性获得了明显改善。     

Analysis of radiation performances of plasma sheet antenna

A novel concept of plasma sheet antennas is presented in this paper, and the radiation performances of plasma sheet antennas are investigated in detail. Firstly, a model of planar plasma antenna (PPA) fed by a microstrip line is developed, and its reflection coefficient is computed by the JE convolution finite-difference time-domain method and compared with that of the metallic patch antenna. It is found that the design of PPA can learn from the theory of the metallic patch antenna, and the impedance matching and reconstruction of resonant frequency can be expediently realized by adjusting the parameters of plasma. Then the PPA is mounted on a metallic cylindrical surface, and the reflection coefficient of the conformal plasma antenna (CPA) is also computed. At the same time, the influence of conformal cylinder radius on the reflection coefficient is also analyzed. Finally, the radiation pattern of a CPA is given, the results show that the pattern agrees well with the one of PPA in the main radiation direction, but its side lobe level has deteriorated significantly.     

等离子体天线色散关系和辐射场数值计算

研究了电磁波沿轴向对称柱形等离子体天线传播的特性、色散关系及辐射方向图、增益等天线参数.通过对腔体材料介电系数、内外半径、等离子体密度、碰撞频率等参数的分析，结果表明要减小波沿等离子体天线传播的衰减，应当增加等离子体密度，减小碰撞频率，增加等离子体半径，减小腔体厚度，采用介电系数较小的材料.计算了在不同参数条件下，等离子体天线的辐射方向图、增益的变化，这些结果对于等离子体天线的设计很有参考价值. 关键词： 等离子体天线 色散关系 增益 辐射方向图     

作为X激光增益介质的激光等离子体特性

本文报道利用具有空间分辨能力的透射光栅谱仪对以三体复合泵浦实现锂离子(Si~(11+)X光自发辐射放大的增益介质——硅激光等离子体特性的研究。结果表明,等离子体5～100A范围软X线辐射主要来自类氦离子(Si~(12+))到(S~(11+))复合辐射和Si~(11+)(n=3→n=2)跃迁发射的贡献,且它们辐射的最大强度距靶面130μm,对应的电子密度3×10~(20)cm~(-3)与Si~(11+)+1s~23d能级的粒子数相对丰度比36;实验中还观察到Si~(11+)(1s~23d-1s~22p)跃迁发射存在着明显的自吸收现象。     

A class of stochastic evolutions that scale to the porous medium equation

A class of reversible Markov jump processes on a periodic lattice is described and a result about their scaling behavior stated: Under diffusion scaling, the empirical measure converges to a solution of the porous medium equation on thed-dimensional torus. The process can be viewed as a randomly interacting configuration of sticks that evolves through exchanges of stick pieces between nearest neighbors through a zero-range pressure mechanism, with conservation of total stick length.     

脉冲高能准分子激光烧蚀块靶产生等离子体的动力学过程的差分模拟

 利用质量连续性、动量守恒和能量守恒这三个基本方程,研究高能脉冲激光照射块状靶材产生等离子体的物理特性。采用差分法和Pichard迭代法,求解带特定边界条件的流体力学三方程,得出已喷射等离子体的温度、密度和速度的分布的迭代方程,并用计算机进行了数值模拟。     

等离子体云团宽带电磁辐射源的实验研究

通过工质爆燃,产生了具有很宽频谱的电磁辐射。用4个宽带天线从不同方向对球形工质产生的电磁辐射进行了接收测量,并对信号作了频谱分析。实验结果表明:150 g工质爆炸产生的电磁脉冲持续时间为50 ns,上升沿很陡,频谱连续,频率范围为1~4 GHz,峰值频率为2 GHz,功率为2 W。对爆燃型工质产生电磁辐射的机理进行了初步理论探讨,认为等离子体辐射可能是产生电磁辐射的源。     

Characteristics of indirect laser-induced plasma from a thin film of oil on a metallic substrate

Optical emissions from the major and trace elements embodied in a transparent gel prepared from cooking oil were detected after the gel was spread in a thin film on a metallic substrate. Such emissions are due to the indirect breakdown of the coating layer. The generated plasma, a mixture of substances from the substrate, the layer, and the ambient gas, was characterized using emission spectroscopy. The characteristics of the plasma formed on the metal with and without the coating layer were investigated. The results showed that Al emission induced from the aluminum substrates coated with oil films extends away from the target surface to ablate the oil film. This finally formed a bifurcating circulation of aluminum vapor against a spherical confinement wall in the front of the plume, which differed from the evolution of the plasma induced from the uncoated aluminum target. The strongest emissions of elements from the oil films can be observed at 2 mm above the target after a detection delay of 1.0 μs. A high temperature zone has been observed in the plasma after the delay of 1.0 μs for the plasma induced from the coated metal. This higher temperature determined in the plasma allows the consideration of the sensitive detection of trace elements in liquids, gels, biological samples, or thin films.     

等离子体云团宽带电磁辐射源的实验研究

通过工质爆燃,产生了具有很宽频谱的电磁辐射。用4个宽带天线从不同方向对球形工质产生的电磁辐射进行了接收测量,并对信号作了频谱分析。实验结果表明：150 g工质爆炸产生的电磁脉冲持续时间为50 ns,上升沿很陡,频谱连续,频率范围为1～4 GHz,峰值频率为2 GHz,功率为2 W。对爆燃型工质产生电磁辐射的机理进行了初步理论探讨,认为等离子体辐射可能是产生电磁辐射的源。     

装置参数对狭缝天线激发的等离子体表面波传播的影响

采用时域有限差分法对矩形结构装置的等离子体表面波传播进行了三维数值模拟.研究了装置参数(如介质板相对介电常数、厚度以及介质板上方空气间隙)对天线阵列激发的等离子体表面波传播的影响,给出了合适的介质板相对介电常数和厚度,并指出空气间隙的存在会严重削弱天线阵列对表面波的激发.计算结果可为大面积矩形表面波等离子体源装置的优化设计提供参考. 关键词： 时域有限差分法 等离子体表面波 狭缝天线     

弱电离尘埃等离子体的介电张量研究

忽略磁场作用,通过求解含BGK碰撞项的Boltzmann方程和尘埃粒子充电方程导出了弱电离尘埃等离子体介电张量的表达式.证明了“冷”尘埃等离子体的纵向介电张量系数与横向介电张量系数相等.完善了弱电离尘埃等离子体电磁特性的理论模型. 关键词： 弱电离尘埃等离子体 Boltzmann方程 充电方程 介电张量