Directional and polarization radiation characteristics of a horizontal impedance vibrator located above a rectangular screen

An algorithm of calculation of the directivity, energy, and polarization radiation characteristics of an arbitrarily oriented thin impedance vibrator located above a rectangular screen is developed on the basis of the asymptotic solution to the 3D problem of diffraction of the field of the electric vibrator by a perfectly conducting rectangular screen. The asymptotic expressions for the current of an impedance vibrator having the electric length 0.4 ≤2l/λ ≤ 0.6 are applied. The asymptotic solution is obtained on the basis of the method of the uniform geometric diffraction theory. The aforementioned characteristics are studied in the whole observation space in the far zone. The effects of the thickness and length of the vibrators and the effects of the distances from the screen on the resonance values of the distributed surface impedance and the corresponding radiation characteristics are shown. The resonance vibrator’s radiation characteristics that depend on the screen dimensions are analyzed. The amplitude and polarization patterns of a horizontal vibrator located above a square screen having optimal dimensions are calculated.     

Fields of horizontal currents located above the Earth

The plane-wave spectrum technique is used to derive the field of horizontal currents located in a horizontal plane above the Earth. The far field is derived asymptotically, and the near field is computed by a two-dimensional fast Fourier transform. Specific numerical results are presented for a pair of oppositely directed dipoles, and the results have application to detection of buried objects. When the antenna is located at low heights, the field is enhanced in the Earth and decreased in the air     

On the impedance of a finite-length horizontal wire located near the Earth's surface

Suitable engineering expressions for the external impedance per unit length of a finite-length horizontal electric antenna located near the earth's surface are derived by employing finitely conducting earth-image-theory techniques. The results should be applicable to horizontal wire antennas employed in the ELF band (1 to 3000 Hz).     

The transient electromagnetic field of a pulsed line source located above a dispersively reflecting surface

An exact representation for the transient field of a pulsed line source above a plane reflecting surface is obtained as a finite integral over the transient plane-wave solution for complex angles of incidence. When applied to the reflection from a conducting half-space, a solution for the transient field is obtained as a finite double integral, which permits accurate calculations in a minimum of computer time. Comparison with early-time and late-time approximations available in the literature shows that there is a wide range of times for which neither is accurate.     

Synthesis of a circular polarized field radiated by an electric dipole located over a rectangular screen

A radiating system consisting of a rectangular perfectly conducting screen and an oblique electric dipole is considered. An algorithm taking into account diffraction by the edges of the screen is developed for determination of the dipole’s slope angle such that the radiated field is circularly polarized in the principal observation planes. The effect of the dipole position relative to the screen on the polarization properties and gain of the system radiating a circularly polarized field is investigated. It is shown that these characteristics exhibited in a given direction can be optimized through selection of the dipole’s position and slope angle.     

Theory of a vertical tubular antenna located above a conducting half-space

The input admittance and the current distribution of a finite vertical tubular dipole antenna located above an infinite dissipative half-space can be found as a function of the distance above and the electric properties of the dissipative half-space. An integral equation for the current on the surface of the antenna is formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane. The magnitude, but not the distribution, of the current is found to be strongly affected by the presence of the dissipative medium. At certain distances above the half-space, the input conductance of the antenna reaches its maximum value.     

Multiple scattering of EM waves by dielectric spheres located in the near field of a source of radiation

An analysis of multiple scattering of electromagnetic (EM) waves by two loss-free dielectric spheres with radii greater than a wavelength and located in the bear field of a source of radiation is presented. The incident field is expressed in terms of spherical vector wave functions (SVWF). Translational and rotational addition theorems are employed to express the SVWF of the incident field in the coordinate system associated with the dielectric scatterer. Numerical computations are performed for obtaining the amplitude and phase patterns of fields multiply scattered by two loss-free dielectric spheres, whose centers are located on the boresight axis and in the nearfield of an open-ended circular cylindrical waveguide excited in its dominant mode. Numerically computed results show good agreement with measured results obtained from a systematic experimental study on forward scatter performed in theX-band.     

New representation for the current in a horizontal wire above ground

A new approximate formula is given for the current in a horizontal wire above ground. This formula, which is more accurate than previous ones, involves contributions from both proper and improper modes.     

Subsurface electromagnetic fields of a circular loop of current located above ground

The electromagnetic fields produced by a circular loop of current is considered for a homogeneous half-space model of the earth. The integral representations for the subsurface field are evaluated numerically and presented in graphical form.     

实现模拟方形分画面的三种新方法

在分析水平、垂直分画面原理的基础上，提出了方形分画面的３种新的实现方法，并详细分析了形成方形画面的过程。     

The radiation efficiency of a dipole antenna located above an imperfectly conducting ground

The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.     

Radiation from a line charge source located near an air-piezoelectric interface

The ray optical solution to the problem of a time harmonic line charge source radiating acoustic energy into a semi-infinite piezo-electric half space is outlined. This ray optical technique differs from the approach employed in recent publications [1], [2], and leads to a better understanding of bulk-wave radiation in SAW devices. PZT ferroceramic materials have been chosen for this study and numerical results are obtained and given.     

Validity of the quasi-TEM approximation for the modes supported by a horizontal wire above ground

The error of the quasi-TEM approximation to the propagation constant for a horizontal wire above ground is estimated. It is shown that the error is likely to be higher for proper modes in a wide range of the parameters defining the propagation conditions.     

雷电近区电场峰值及其变化率随距离的变化研究

人工引雷试验对前端测量装置的电源稳定供应和恶劣环境下的工作可靠性要求较高. 为了解决传统电池供电电场传感器持续工作能力不足以及强雷暴环境下的试验安全等问题,研制了一套基于光纤供能的雷电电磁脉冲电场测量系统. 系统电源供给、信号测量和数据监控传输均通过光纤连接,采用STM32微处理器进行监控,具有电源管理、传输比在线校准和温度在线监测功能. 介绍了系统的主电路设计,并对系统的功能和性能进行了试验测试. 结果表明：在夏季环境温度26～40 ℃的情况下,通过光纤供能的光伏电池能够持续稳定工作,测量系统−3 dB带宽达到33 MHz;通过3组不同灵敏度天线切换,可用量程范围为0.18~117 kV/m,满足人工引雷通道近区电场的测量需求.     

雷电近区电场峰值及其变化率随距离的变化研究

闪电近区电场具有瞬时性和高强度的特点,在雷电防护工程设计及雷电效应测试中,往往需要根据雷电所产生的脉冲辐射强度采取相应的防护、测试措施,在雷电防护标准规范中应明确给出距离雷电通道不同距离处的电场峰值及其变化率的变化情况.文中在传输线（transmission-line,TL）模型的基础上,对雷电近区电场峰值及其变化率随距离的变化进行近似表达,并与相关文献报道的实测数据进行了对比.结果表明,近似表达式的结果与文献报道的实测数据及课题组野外实际观测数据较为吻合,可用于表征距离雷电通道1 km范围内电场峰值和电场变化率的变化,对实际防雷设计和相关的效应测试具有一定的指导意义.