Transient response of an infinite cylindrical antenna in a dissipative medium

The transient solution of an infinite cylindrical antenna in a dissipative medium caused by an impulse excitation at a delta gap is obtained via an exact solution in the form of definite integrals and a simple asymptotic formula. This formula is used to obtain an integral for calculating the antenna current caused by a double exponential input voltage at the gap; furthermore, the resulting integral reduces to Sunde's classic result under the diffusion limit. These results are applied to the transient response of a buried wire subject to an electromagnetic pulse (EMP) or nearby lightning incident wave.     

Transient response of the infinite cylindrical antenna and scatterer

The transient response of an infinite cylindrical antenna and scatterer is obtained by time gating a time-dependent electric-field integral equation for thin wires of finite-length. The driving point current and broadside radiated field approximate the driving point voltage in the antenna case, while the current excited in the scattering case approximates the time integral of the incident field. This approximate integral relation is used to estimate currents excited on cylindrical structures without employing the complete integral equation solution procedure.     

Admittance of an infinite cylindrical antenna with realistic gap field

A numerical comparison is made between the admittance of an infinite cylindrical antenna excited by a realistic electric field across a finite gap, and the admittance found by assuming a constant electric field in the same gap. A simple approximate relation between the two is derived, while a second simple expression shows how the admittance changes as the gap width is varied.     

Current waves on an infinite cylindrical antenna in a warm plasma

The current waves on the outside wall of an infinite cylindrical antenna, fed by a delta-function generator and immersed in a warm isotropic plasma, which is in direct contact with the antenna, is separated into its components: the familiar e.m. wave, the `transverse-plasma? wave and the slow surface wave.     

Properties of a cylindrical antenna in an infinite planar or collinear array

A solution is given for the active impedance and current distribution on a cylindrical antenna in a uniform, infinite, planar, or collinear array. The analysis is applicable to the case in which the distance in the collinear direction between the ends of adjacent elements is small. The current distribution on the collinear array is found by relating the antenna current and electric-field variation on the cylindrical surface of infinite length which contains the array. This analysis is then extended to consider a planar array. Results obtained are applicable to any combination of element length and array phasing, for arrays with or without a ground plane. Comparisons with other investigations based upon sinusoidally distributed currents reveal substantial discrepancies for some configurations.     

Current distribution and input admittance of an infinite cylindrical antenna in anisotropic plasma

The current distribution and input admittance of an infinitely long cylindrical antenna driven by a slice generator and immersed in an anisotropic plasma are investigated. The applied dc magnetic field is along the axis of the antenna. By superimposing the characteristic waves guided along the antenna, the current solution is obtained in the form of a one-dimensional integral, which is examined both analytically and numerically. WhenK_{perp} > 0, the magnitude of the current decays slowly with the distance from the source, and its phase is nearly linear with a "propagation constant" equal tosqrt{K_{perp}}k_{0}for an antenna with very small radius. WhenK_{perp} < 0, the magnitude of the current decreases rapidly away from the source, and its phase is no longer linear. The input admittance decreases with the radius of the antenna.     

Radiation characteristics of an infinite dielectric-coated axiallyslotted cylindrical antenna partly embedded in a ground plane

The radiation characteristics of an axial slot on a dielectric-coated conducting circular cylinder embedded in a semi-circle in an infinite ground plane (GP) are examined. The boundary-value method is employed to obtain the solution with the aid of the partial orthogonality of the trigonometric functions. The resulting dual infinite series involved in the solution is then truncated to generate numerical results. The geometry considered here is important because it can be implemented on the body of any mobile communication system. Moreover the GP adds a new parameter to the slotted dielectric-coated conducting circular cylindrical antenna and can be used in beam shaping and to enhance the antenna performance     

The admittance of the infinite cylindrical antenna immersed in a lossy, compressible plasma

Some numerical results obtained from an analysis of the admittance of an infinite cylindrical antenna excited at a circumferential gap of finite thickness and immersed in a lossy, compressible (warm) plasma are given. The linearized hydrodynamic equations are used for the electrons (ion motion is neglected). A free-space layer, or vacuum sheath, is used to approximate the ion sheath which forms about an object at floating potential in a nonzero temperature plasma. Values for the antenna admittance are obtained by a direct numerical integration of the Fourier integral for the current, and are presented as a function of frequency for plasma parameter values typical of theEregion of the ionosphere. The admittance exhibits a maximum below the plasma frequency unless the electron temperature and sheath thickness are both zero; however, above the plasma frequency, the sheath and electron temperature have relatively little effect on the antenna admittance. The nonzero plasma temperature considerably enhances the antenna conductance below the plasma frequency compared with the zero-temperature case while at the same time reducing the dependence of the conductance on the electron collision frequency. A susceptance zero the location of which is not sensitive to the vacuum sheath thickness occurs near the plasma frequency.     

Analysis of a cylindrical antenna containing an aperture coupledload

In this paper we present the basis for the analysis of shielded tuning networks coupled to wire antenna elements. The structure analyzed comprises three conducting cylindrical tubes that form an aperture-fed circular coaxial waveguide. Two methods are presented for formulating and solving integral equations for the structure. The first method is based on the mixed potential electric field integral equation enforced on the three cylindrical tubes, and the second is based on aperture theory. An end correction capacitance is used to adjust the reflection coefficient in the eigenmode expressions of the aperture method. The data obtained by the two methods are in close agreement. Differences in actual currents and equivalent currents obtained from solutions are discussed and reconciled     

高功率微波作用下单极天线瞬态响应特性研究

运用时域有限差分法(FDTD)结合同轴等效馈电模型计算了高功率微波(HPM)电磁脉冲作用下单极天线的感应电流的频域和时域响应,分析了单根单极天线感应电流频谱和时域响应与入射HPM间的关系,同时分析了两根天线间的距离对第一根天线末端感应电流的影响。计算结果表明,单根单极天线对HPM的感应电流频谱主要由入射HPM载波频率决定,感应电流波形与入射HPM波形相似;有其他天线存在时,对第一根天线会造成影响,且随距离增加影响减小。     

Electromagnetic response of an anisotropic cylindrical shell

A remarkably simple and novel solution is obtained for the fields induced in an anisotropic cylindrical shell that is located coaxially within a long solenoid. This could be the basis of a nondestructive measuring scheme for stranded wire rope.     

Leaky-mode cylindrical dielectric resonator antenna

A cylindrical dielectric resonator (CDR) antenna, operating in leaky TM-modes, is presented. The antenna is composed of the CDR, short-circuited by parallel rectangular conducting plates. The radiation pattern depends on the size and shape of conducting plates. This technique provides an opportunity to change the radiation pattern without affecting antenna resonant frequency. Numerical examples based on the integral equation method are presented to show advantages of this design     

A cylindrical Fresnel zone antenna

A cylindrical Fresnel zone antenna as a candidate for a base station in wireless indoor LAN systems is described. An arbitrary angle-tilted fan beam in azimuth can be achieved by moving the position of the strip dipole feed at the cylinder center. A simple theory based on the diffraction integral is developed which predicts the antenna radiation characteristics. The antenna fabrication and measurement are carried out at 9 GHz with good agreement between calculated and measured results     

Switchable cylindrical dielectric resonator antenna

A switchable cylindrical dielectric resonator antenna operating in four different radiation modes is reported. Two linear polarised, one circular polarised, and a nonradiating mode are implemented. The experimental results of the resonant frequency, boresight axial ratio, gain, unloaded Q-factor, impedance bandwidth and radiation efficiency are presented for the operating modes and compared with the theoretical values     

The cylindrical omnidirectional patch antenna

The need for omnidirectional (in the azimuth plane) antennas with narrow beams in the elevation plane, for wireless applications has increased considerably. The antennas are used in many frequency bands anywhere from 0.8 to 6 GHz, in a variety of configurations. The different collinear-array configurations are designed using back-to-back wide-beam elements or by simply using radiating elements with an intrinsic omnidirectional pattern. The motivation for this work was to devise a radiation element which has an omnidirectional pattern in the azimuth plane and allows for the design and fabrication of arrays that can be easily integrated with other collinear arrays to generate a multitasking omnidirectional antenna. The element proposed in this paper is a patch, which was built in a cylindrical geometry rather than a planar one, and which generates an omnidirectional pattern in the azimuthal plane     

Pattern synthesis of cylindrical slot antenna

A constrained synthesis procedure is applied to the cylindrical slot antenna. Sets of orthogonal eigenfunctions are generated to represent the aperture and radiation fields. The error criterion is that of the minimum mean-square match and the super-gain ratio represents the source constraint. The method is illustrated for the cosecant pattern.