Far field radiation from an arbitrarily oriented Hertzian dipole in the presence of a layered anisotropic medium

Far field radiation from an arbitrarily oriented Hertzian dipole for two-layered uniaxially anisotropic medium with a tilted optic axis is treated analytically by using the dyadic Green's function of the problem when the dipole is placed over or embedded in a two-layered uniaxially anisotropic medium. The radiation fields are evaluated using the steepest descent method. Parameter studies including anisotropy, layer thickness and dipole location are performed to investigate the effects of changing different variables on the radiation fields. Results of this work can be applied in microstrip circuits and antennas.     

Electromagnetic field of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium

The electromagnetic fields of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium are studied. There are three media, one-dimensionally anisotropic medium covered with a dielectric under the air. The electromagnetic field components are complex because of the multiple reflections from the up and down boundaries. The electromagnetic field components between air and one-dimensionally anisotropic medium are given, the trapped surface waves and lateral waves along the dielectric-anisotropic medium boundary are computed. The results have some practical applications in the communication in sea or lake above one-dimensionally anisotropic earth or sediments.     

Spectral resolution and solution of field problems in an anisotropic and compressible medium

It is shown that when source currents are present in a compressible and anisotropic plasma, the longitudinal components of the electric and magnetic fields and the pressure variation satisfy a coupled inhomogeneous equation. Based on the spectral resolution of a square matrix, a general method for the solution of such an equation is presented. The solution of the coupled-wave equation is thus reduced to the evaluation of some simple integrals. Formulas for the determination of the transverse components are given. To demonstrate the simplicity of the method, fields due to a magnetic line source are worked out in detail. Some numerical results are also included.     

Numerical solution of dipole radiation in a compressible plasma

The electric current and surface electron distributions for a dipole antenna in a compressible plasma are solved numerically. The results also include the input impedance and the upper limit of the driving voltage below which the small signal approximation is valid.     

Radiation from a uniformly moving distribution of electric charge in an anisotropic, compressible plasma

The radiation characteristics of a linear distribution of electric charge moving with a uniform velocity in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform static magnetic field is impressed externally throughout the medium. The linear distribution of charge and its direction of motion are assumed to be parallel and perpendicular, respectively, to the direction of the external magnetic field. Of the two possible modes of waves of small amplitude, namely, the modified electromagnetic mode and the modified electron plasma mode, the uniformly moving charge distribution excites the modified electron plasma mode. The emitted radiation has no frequencies less than the plasma frequency. For a particular value of the ratio of the gyrotropic to the plasma frequency of the electrons, the frequency and the angular spectrum of the emitted radiation are determined for two values of the velocity of the charge.     

磁偶极在各向异性媒质中辐射的能流密度

对各向异性媒质中辐射问题的研究,求出磁偶极在各向异性媒质中辐射的具有张量形式的能流密度的普遍公式,在直角坐标系中,通过并矢计算,得出磁偶极在各向异性媒质中辐射的平均能流密度,并对磁偶极在各向异性媒质中的辐射作出了主要集中方向的判断,为研究各向异性媒质的开发应用提供了一个理论依据.对导出的新公式进行了验证.     

The field of a dipole enclosed in an elliptic anisotropic plasma cylinder

The boundary value problem for the field of an electric dipole enclosed in a thin elliptic anisotropic plasma cylinder with a vacuum cavity is considered. A solution to the problem is obtained and analyzed. The influence of a magnetic field and the cavity of variable size on the resonance electromagnetic field is studied in the case when the shape of the plasma cylinder’s cross section varies. The effect is compared to that observed in the case of a circular plasma cylinder.     

Radiation from an electric dipole in an axially magnetised plasma column

Some aspects of radiation from an axially oriented electric dipole situated at the centre of an infinitely long axially magnetised column of uniform plasma are treated. For various frequencies below the plasma frequency and for a particular radius of the plasma column, selected results on the radiation pattern and the radiation resistance are presented as a function of the magnetostatic field. These results indicate that significant improvement in transmission through a moderately dense plasma sheath can be obtained by a suitable application of a static magnetic field.     

Fields of an electric dipole perpendicular to a magnetostatic field in a hot plasma

The radiation fields of an electric dipole oriented perpendicular to the magnetostatic field in a hot uniaxial plasma are considered. The behavior of the fields near the resonance cone for the perpendicular and parallel orientations are found to be similar. A procedure is shown for estimating the electron temperature and density by measurements on the characteristic angular distribution of the fields near the resonance cone.     

Radiation resistance of an oscillating dipole in a moving compressible plasma

The radiation resistance of an electric dipole located in a moving compressible plasma is treated. First, the wave equations for a uniformly moving compressible plasma in the presence of a current source without any restriction upon the magnitude of the velocity are derived. Then, using these wave equations the radiation resistance of the present problem is obtained and its characteristics are investigated numerically. It is shown that if the moving velocity of plasmaupsilon_{0}exceeds the thermal velocity of the electronupsilon_{t}, a region appears in which the plasma wave component of the radiation resistance becomes negative. In this case, the numerical calculation shows that there is a range ofupsilon_{0}where the radiation efficiency of the electromagnetic wave is much improved. The cutoff frequency of the plasma wave in a moving compressible plasma becomes lower than that of the plasma wave in the rest frame of the plasma.     

On waves in an anisotropic plasma imbedded in a moving dielectric medium

The governing equations for electromagnetic fields in an anisotropic plasma imbedded in a moving dielectric medium are obtained. Examination of the wave and dispersion equations yields information on the elliptically or linearly polarized waves which may exist when the external magnetic field is parallel or perpendicular to the direction of motion, respectively.     

Radiation resistance of an electric dipole in a magnetoionic medium

Radiation resistance for an elementary electric dipole immersed in a magnetoionic plasma is investigated. Based on an integral expression obtained by Kogelnik, extensive numerical results are obtained and discussed. In addition a simple analytic expression is derived for the case of small magnetic fields.     

Approximate formulas for lateral electromagnetic pulses from a horizontal electric dipole on the surface of one-dimensionally anisotropic medium

In this paper, approximate formulas are derived for the electromagnetic pulse due to a delta-function current in a horizontal electric dipole on the planar boundary between a homogeneous isotropic medium and one-dimensionally anisotropic medium. The components of the electric field consist of two delta-function lateral pulses which decrease with the amplitude factor /spl rho//sup -2/ and travel along the boundary with different velocities and different amplitudes. Also, it is noted that the formulas for the time-dependent magnetic field components obtained by Fourier transforms from the approximate formulas in the frequency domain are not adequate.     

Propagation of EM pulses excited by an electric dipole in aconducting medium

Exact solutions are given for the transient electromagnetic (EM) fields excited by an electric dipole antenna with an impulsive current in a conducting medium. There exists an optimum waveform for the antenna current which can generate an EM pulse with a maximum intensity at a particular distance from the antenna. It is found that the EM fields of an EM pulse excited by an antenna in a conducting medium can be divided into two parts. The first part is an impulse wave which propagates with the speed of light (1/√(μϵ)) and decays exponentially. The second part builds up gradually and propagates slowly, and more importantly this part attenuates as an inverse power of distance which is a much slower rate than an exponential decay     

On the radiation Q and the gain of crossed electric and magnetic dipole moments

Exact expressions for the radiation quality factor Q and the gain pattern function of the corresponding antenna are derived and their properties are analyzed for crossed electric and magnetic dipole moment configuration. Both omni-directional and directional antennas with linear, elliptical, or circular polarization can achieve the same minimum radiation Q. The maximum gain of the antenna ranges from 3/2 to 3. The maximum gain of three can be achieved only for linear polarization when the source vectors make a right angle and the amplitudes of the TM and the TE modes are equal. The increase in the maximum gain from 3/2 for omni-directional antennas to 3 for directional antennas does not require any increase in the radiation Q, which suggests that practical directional antennas with higher gain may be realized with smaller size compared with small omni-directional antennas assuming similar operation bandwidths.     

Waves along a cylindrical "Grid-like" antenna in an anisotropic compressible plasma

In an anisotropic compressible homogeneous plasma, the dispersion equation of waves along an infinitely long cylindrical "grid-like" antenna is obtained analytically. Numerical solutions of this equation show that an external static magnetic field has great influence upon the anomalously dispersive region of the dispersion relation around the plasma frequency.     

Radiation in a warm plasma from an electric dipole with a cylindrical column of insulation

The radiation in a warm plasma due to an axially oriented electric dipole on the axis of a cylindrical column of insulation of infinite length is studied using the linearized continuum plasma theory, and approximate boundary conditions. Two types of surface waves are excited along the cylindrical column of free space immersed in a plasma and their dispersion and power relations are examined. The uncoupled electromagnetic (EM) and the plasma (P) space waves are excited. The radiation pattern and the normalized radiation resistance of the EM and the P modes are studied both as a function of frequency and as the radius of the insulating column. The effect of the insulating column is found to be very significant only in the case of the P mode. It is found that the power transfer into the P mode becomes less at higher frequencies and larger thickness of the insulation. The results of this investigation may be used to predict in a crude manner the effect of the "ion sheath" that is formed around the antenna in the ionosphere.     

Green dyadic and dipole radiation in triaxial omega medium

A triaxial omega medium, which can be artificially realised by embedding three types of omega-shaped particles in an isotropic host medium, is proposed. The Green dyadic and the electromagnetic field of a dipole radiator are presented, by introducing a set of auxiliary fields and coordinate transformation