共查询到19条相似文献,搜索用时 187 毫秒
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为了深入分析能量选择防护结构(ESS)等周期结构作为天线罩时与天线产生的耦合效应,提高分析效率,该文提出一种基于坡印廷矢量法的耦合效应分析方法。该文从收发互易的角度,将天线当作发射器而非常规方法中的接收器对天线的电磁特性进行分析。从接收的角度理解,天线是一种从自由空间中捕获能量的装置,而能量分布可以通过坡印廷能流密度曲线来描述。同样地,能量选择防护结构对电磁波的扰动也可以通过能流密度曲线来描述。因此,天线、防护结构以及二者的耦合效应均可通过能流密度曲线进行研究和分析。结果表明,该文所提方法与常规分析方法具有良好的一致性。相比于常规分析方法,该文方法可同时对天线与防护结构的耦合效应进行可视化分析与量化评估,指导防护结构的尺寸、形状设计以及最佳安装位置,显著提高设计效率。 相似文献
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针对低频电磁传输中天线尺寸过大的问题,设计了一种基于三相感应电机的小型化超低频发射天线.电机工作时产生了时变低频电磁场,可作为超低频发射天线.为有效分析其电磁场分布,文章建立旋转磁偶极子数学模型以等效电机内部旋转时产生的磁场.首先,对电机内部磁场和旋转磁偶极子的关系进行阐述,利用麦克斯韦方程组,得到旋转磁偶极子的电磁场分布.其次,通过电磁仿真软件验证旋转磁偶极子的近场分布特性和远场辐射特性.最后,通过实验对电机近场的磁场分布进行验证.仿真和实测结果表明,三相感应电机具有超低频天线的辐射特性. 相似文献
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瞬态电磁脉冲能量传输特性的物理实质 总被引:1,自引:0,他引:1
根据矢量位方程,在均匀电流模型下,分别给出了圆形和方形单元天线轴线上电磁场分量的时域表达式以及能量密度的解析计算公式;用等腰梯形电脉冲给天线馈电,采用数值计算的方法分别绘出了圆形和方形天线轴线能量密度随距离的衰减曲线,瞬态电磁脉冲能量传输呈现三段式传输规律和慢衰减特性;通过对能量密度解析计算公式物理意义的讨论,给出了瞬态电磁脉冲慢衰减传输特性的物理实质解释;采用亚纳秒电子源给抛物面天线馈电,对抛物面天线轴线辐射电磁脉冲波形及能量作实验测试,实验测试结果与数值计算结果相符合。 相似文献
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分析了求解对称振子输入阻抗的计算方法,包括近似方法(坡印廷矢量法、等效传输线法和感应电动势法)、解析方法(海伦积分法)和数值方法(矩量法),计算了不等长平行对称振子的互阻抗. 着重对等效传输线法和海伦积分法进行了分析和研究,对等效传输线法存在的不足进行了修正,推导了海伦积分法计算输入阻抗的各个参数,并将修正后的等效传输线法计算结果与海伦积分法和矩量法的计算结果进行了比较. 结果表明,修正后的计算方法适用于一般对称振子. 相似文献
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为解决计算区域的大尺度与天线尺寸的小尺度问题, 将复合网格法应用于近场通信(Near-Field Communication, NFC)天线等效电路参数的提取与计算, 该方法可以在计算效率和计算精度之间达到很好的平衡.为避免麦克斯韦方程的“低频崩溃”问题, 低频位移电流很小时, 采用静态场方法分析低频NFC天线的近场参数.其中对线圈天线分布电容的计算不同于以往的实验测量、理论估算和数值计算等研究方法, 而是基于其定义计算线圈相对于接地点的电容, 该方法可以得到与参考文献一致的计算结果, 同时具有能够分析周围环境对分布电容影响的优点.通过有限元分析, 将复合网格法与均匀网格法的计算结果对比, 证明了复合网格法在三维电磁场应用的可能性以及准确性. 相似文献
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FDTD软件中S参数提取方法的讨论与分析 总被引:1,自引:0,他引:1
利用基于时域有限差分(FDTD)的电磁场数值仿真软件,如XFDTD等对传输线、天线等结构进行仿真计算时,只能提取激励点的S参数,而在实际应用中,需要提取传输线等结构任意截面的S参数。针对该问题,本文采用坡印亭矢量和驻波比两种方法,通过XFDTD软件输出的稳态场分布获得S参数,并与传输线理论计算所得S参数进行比较,验证了这两种方法的可行性。 相似文献
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Sten J.C.-E. Hujanen A. Koivisto P.K. 《Antennas and Propagation, IEEE Transactions on》2001,49(5):829-837
Expressions are derived for the smallest achievable radiation quality factor (Q) of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of non-propagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation Q is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the method of moments), and the approximate Q obtained from their fractional bandwidth are compared to the corresponding theoretical minima 相似文献
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《Microwave Theory and Techniques》1981,29(6):588-594
The power absorption characteristics of the prolate spheroidal model of an average man have been studied when the model is exposed to the near fields of an arbitrarily located small loop antenna. An integral equation is formulated and the fields radiated by the loop are expanded in terms of the vector spherical harmonics. This equation is then solved using the extended boundary condition method (EBCM,). For three different loop-spheroid configurations, the power distribution and the average SAR have been calculated as a function of the frequency and the separation distance. It is shown that the results obtained for separation distances larger than lambda /2 agree well with those obtained from the plane wave exposure case. Furthermore, the average SAR value calculated as a function of separation distance for the case where the magnetic dipole moment is aligned parallel to the major axis of the spheroid are found to oscillate around the constant value obtained from the H-polarized plane wave exposure case. On the other hand, the average SAR values for the E-polarization case (magnetic dipole is parallel to the spheroidal minor axis) are found to increase monotonically with the decrease in separation distance. It is also shown that despite the complicated nature of the near fields, the absorption characteristics can still be explained in terms of the variations of the incident radiation. These loop results, together with those obtained from other simple soures, can be used as building blocks in arriving at a qualitative understanding of the near-field absorption characteristics for more general exposure cases. 相似文献
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根据半导体光电子学理论,分析了光注入非平衡载流子(电子-空穴对)的瞬态输运机理,研究了不同条件下的SI-GaAs光电导偶极天线太赫兹波辐射功率和辐射强度的饱和效应.结果表明其主要原因是在外加偏置电场作用下,光注入载流子出现了空间电荷电场屏蔽和辐射电场屏蔽现象,对提高太赫兹波辐射功率和辐射强度起到了遏制作用.对于电极间隙大小不同的天线,两种屏蔽效应的作用不同;在触发光能一定的情况下,照射光斑较大时屏蔽效应较小. 相似文献
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A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Green's function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4×4 microstrip array is presented to validate the theory 相似文献
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《Microwave Theory and Techniques》1980,28(7):801-807
Analysis of the near-field irradiation of prolate spheroidal models of humans and animals by a short electrical dipole is described. The method of solution involves an integral equation formulation of the problem in terms of the transverse dyadic Green's function and expanding the fields irradiated by a short dipole in terms of the vector spherical harmonics. The extended boundary condition method (EBCM) is employed to solve the integral equations. The power distribution and the average specific absorption rate (SAR) are calculated and plotted as a function of the separation distance. It is shown that for a dipole placed along the major axis of the spheroidal (k-polarization), and for a very short separation distance, d= 0.15 lambda, the relative power values at both ends of the spheroid are about 40 compared with the ratio of 15 in the planewave exposure case. Furthermore, the calculated average SAR values as a function of the separation distance were found to oscillate around the constant value obtained from the planewave irradiation case. Differences between the near-and far-field exposure cases occurred only at separation distances shorter than 0.5 lambda where the magnitudes of the electric and magnetic energy densities are higher than the time-average radiation power density. 相似文献
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Electrically small antennas are generally presumed to exhibit high impedance mismatch (high VSWR), low efficiency, high quality factor (Q); and, therefore, narrow operating bandwidth. For an electric or magnetic dipole antenna, there is a fundamental lower bound for the quality factor that is determined as a function of the antenna's occupied physical volume. In this paper, the quality factor of a resonant, electrically small electric dipole is minimized by allowing the antenna geometry to utilize the occupied spherical volume to the greatest extent possible. A self-resonant, electrically small electric dipole antenna is presented that exhibits an impedance near 50 Ohms, an efficiency in excess of 95% and a quality factor that is within 1.5 times the fundamental lower bound at a value of ka less than 0.27. Through an arrangement of the antenna's wire geometry, the electrically small dipole's polarization is converted from linear to elliptical (with an axial ratio of 3 dB), resulting in a further reduction in the quality factor. The elliptically polarized, electrically small antenna exhibits an impedance near 50 Ohms, an efficiency in excess of 95% and it has an omnidirectional, figure-eight radiation pattern. 相似文献
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J. D. Hunter 《International Journal of Electronics》2013,100(3):183-191
The use of a magnetic dipole to represent a small loop antenna is examined by comparing their field components. Particular attention is paid to the dipole approximation in the near field, and curves are presented which allow an accurate and rapid assessment to be made of the error as a function of angle and distance from the loop. The curves, which apply to any loop with a circumference between 0.0001 λ and 0.1 λ, enable the correction to the dipole field to be estimated. The difference between the loop and magnetic dipole fields is expressed algebraically for large distances from the loop, and for near-axial angles. 相似文献
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A method is developed for calculating the radiation efficiency and quality factor, Q, for azimuthally symmetric electric (Tm) and magnetic (Te) multipole fields surrounded by a semi-transparent spherical shield of variable thickness, dielectric and magnetic constants involving losses. A matrix method is used to connect the transverse field components at adjacent interfaces. The Q and efficiency are determined by computing the energy stored in the near field of the multipole as well as the power radiated and dissipated in the shield. A numerical comparison of the performance of electric and magnetic dipole radiators is given as a function of frequency. An expression is derived for the permittivity of the shield which optimisés the Q. 相似文献
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Standard probes for electromagnetic field measurements 总被引:6,自引:0,他引:6
Discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The standard probes described are an electrically short dipole, a resistively-loaded dipole, a half-wave dipole, an electrically small loop, and a resistively-loaded loop. A single-turn loop designed for simultaneous measurement of the electric and magnetic components of near-fields and other complex electromagnetic environments is also described. Each type of antenna demonstrates a different compromise between broadband frequency response and sensitivity 相似文献