The diffraction of an inhomogeneous plane wave by an impedancewedge in a lossy medium

The diffraction of an inhomogeneous plane wave by an impedance wedge embedded in a lossy medium is analyzed. The rigorous integral representation for the field is asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD) so that the asymptotic expressions obtained can be employed in a ray analysis of the scattering from more complex edge geometries located in a dissipative medium. Surface wave excitations at the edge and their propagation along the wedge faces are discussed with particular emphasis on the effects of losses     

Investigation of diffraction of an electromagnetic wave arbitrarily incident on a locally inhomogeneous medium interface

The 3D problem of reflection of a plane electromagnetic wave by an irregular boundary containing a locally inhomogeneous well conducting section is considered. The boundary value problem for the system of Maxwell equations in an infinite section with an irregular boundary is reduced to the solution of systems of singular equations. A numerical algorithm for their solution is developed. Results of calculation of the currents induced on the irregularity and reflected field patterns are presented for the case of the E polarization.     

利用辛几何理论求解电磁波在非均匀媒质中的传播

提出了一种基于辛几何的高频近似的新方法，并用此方法求解了电磁波在一非均匀媒质中的传播问题。通过辛空间上的坐标变换，使电磁波传播中的焦散问题转化为非焦散的问题，并结合几何光学的方法，求得了包括焦散区在内的高频近似解。解决了几何光学法无法在焦散区求解的问题，还可以推广到二维及三维的情况。     

Two-dimensional surface-wave diffraction from an arbitrary source in an anisotropic medium

It is shown that, if a parabolic function approximates closely to the relevant wavenumber surface, the surface-wave diffraction pattern radiated from any source is related, by a simple scale factor, to that launched by the same source into an isotropic medium. The argument, based on resolution of the source into an orthogonal Gaussian?Hermite mode set, may find application both in integrated optics and in the design of acoustic-surface-wave matched filters.     

On electromagnetic wave reflection from a randomly inhomogeneous medium with fluctuations of the complex permittivity

The Einstein-Fokker equation is solved in order to obtain an expression for the probability density of the absolute value of the correcting term for the reflection coefficient of a dielectric layer with 1D fluctuations of the real and imaginary parts of the permittivity. The applicability of the obtained results to studying multiyear ice in the Arctic is discussed, and computation taking into account the corresponding values of the input parameters of the problem is preformed.     

Diffraction of an arbitrary plane electromagnetic wave by a half-plane

The asymptotic form of the diffracted field produced by a plane electromagnetic wave of arbitrary polarization incident obliquely on a conducting half-plane is expressed very simply in terms of the incident and reflected wavesF_{1}andF_{2}, respectively, rotated to bring their wave vectorsk_{1}andk_{2}onkin the direction of observation. The diffraction coefficients becomepm(sin psi_{i}/2)^{-1}wherepsi_{i}is the angle betweenk_{i} (i = 1,2)and the direction of observationk.     

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.     

Reflection of electromagnetic wave from a time-varying medium

For the purpose of radiowave propagation in the ionosphere, in a plasma and in other media, the reflection and transmission of an electromagnetic wave from a suddenly changed conductivity, when a plane wave is normally incident upon an interface separating two conducting media, are studied. The field expressions are exactly obtained through the use of the Laplace transform. The discussion is primarily on the time behaviour of the reflected wave.     

An agar-agar chamber for study of electromagnetic waves in an inhomogeneous medium

A medium for the propagation of electromagnetic waves whose dielectric constant or loss tangent has a prescribed profile was fabricated by using a large quantity of agar-agar in simulation chambers. The dielectric constant of the agar-agar could be changed continuously by means of a controlled diffusion of ethyl alcohol. The loss tangent of the same medium could be changed continuously by means of a controlled diffusion of NaCl. This paper is concerned with the design and characteristics of the simulation chamber. Topics to be considered include the properties of agar-agar in a wide frequency spectrum, the diffusion profiles, a reexamination of the principle of simulation, and the construction of various types of probes and simulation chambers.     

Radiation resitance of an elementary loop antenna in a magnetoionic medium

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

Evaluation of the scattering of an electromagnetic wave from precipitation particles by the use of fredholm integral equations

A new, more general and extremely stable solution to the problem of scattering of electromagnetic waves from precipitation particles is presented, based on the solution of Lippmann-Schwinger type equations in complex Fourier space. We believe that the solution is not so demanding in either computer time or storage as existing methods. It also incorporates the calculation of the scattering amplitude for any incidence angle and polarisation. Results of scattering from oblate axisymmetric spheroidal raindrops at 11 GHz are presented.     

A Luneburg-Kline representation for wave propagation in acontinuously inhomogeneous medium

We derive a Luneburg-Kline (GK) asymptotic series representation for wave propagation in a one-dimensional (1-D) continuously inhomogeneous medium. We set the solution up so that the classical phase function common to the Wentzel, Kramers, Brillouin, and Jeffreys (WKBJ) approximation multiplies all terms of the L-K series. We develop an error criterion for the WKBJ approximation based on the magnitude of an ignored term relative to retained terms in the governing differential equation. Finally, we note that while the validity of the GK series solution is dependent upon a large free-space wavenumber for small to moderate spatial gradients in the index of refraction, large spatial gradients can be accommodated by increasing the free-space wavenumber. Hence, there is a strong similarity of this situation to boundary diffraction problems where rounded edges approach, but do not achieve, absolute sharpness. Loosely speaking, in both instances a scale size in terms of the wavelength is maintained constant     

New method for determining a direction to an electromagnetic radiation source

The method for determining the direction of an electromagnetic radiation source without the interference of signals from two receivers is described.     

Plane-wave spectrum representation of a field in a magnetoionic medium due to a plane distribution of source currents

The fields due to a plane distribution of source currents are formulated, in terms of three-dimensional Fourier transforms, to yield equivalent results obtainable from a representation in terms of an angular spectrum of plane waves introduced by Clemmow. Certain difference in the present field expressions and those given by Clemmow in a recent paper are discussed.     

SOLVING THE PROPAGATION OF ELECTROMAGNETIC WAVE IN A SIMPLE TWO—DIMENSI8ONAL INHOMOGENEOUS MEDIUM BASED ON SYMPLECTIC GEOMETRICAL THEORY

A new symplectic geometrical high-frequency approximation method for solving the propagation of electromagnetic wave in the two-dimensional inhomogeneous medium is used in this paper. The propagating caustic problem of electromagnetic wave is translated into non-caustic problem by the coordinate transform on the symplectic space. The high-frequency approximation solution that includes the caustic region is obtained with the method combining with the geometrical optics. The drawback that the solution in the caustic region can not be obtained with geometrical optics is overcome by this method. The results coincide well with that of finite element method.     

A tunable source of linearly-polarized,near-millmeter wave radiation

GYROTRON III is a cw source of near-millimetre wave radiation that is tunable over the frequency range 75 to 330 GHz. The high-order waveguide modes that are characteristic of tunable gyrotrons are converted into a well-collimated, linearly-polarized beam by means of a quasi-optical or Vlasov antenna.     

A quasi-wave method for determination of a general solution to the complex maxwell equations in an inhomogeneous anisotropic absorbing medium

A formal general solution to the homogeneous Maxwell equations is obtained in the form of a matrix asymptotic series for the case of a quasi-plane-layered medium in which complex tensors \(\hat \varepsilon \) and \(\hat \mu \) arbitrarily depend on Cartesian coordinate zand slowly change in the planes z=const. A recurrent system of matrix first-order linear ordinary differential equations for the coefficients of this series is derived. In contrast to the method of geometric optics, this solution, even in the first approximation, takes into account the wave polarization and has a wider range of application.     

Fast multipole method for scattering from an arbitrary PEC targetabove or buried in a lossy half space

The fast multipole method (FMM) was originally developed for perfect electric conductors (PECs) in free space, through exploitation of the spectral properties of the free-space Green's function. In the work reported here, the FMM is modified, for scattering from an arbitrary three-dimensional (3-D) PEC target above or buried in a lossy half space. The “near” terms in the FMM are handled via the original method-of-moments (MoM) analysis, wherein the half-space Green's function is evaluated efficiently and rigorously through application of the method of complex images. The “far” FMM interactions, which employ a clustering of expansion and testing functions, utilize an approximation to the Green's function dyadic via real image sources and far-field reflection dyadics. The half-space FMM algorithm is validated through comparison with results computed via a rigorous MoM analysis. Further, a detailed comparison is performed on the memory and computational requirements of the MoM and FMM algorithms for a target in the vicinity of a half-space interface