Features of Radiation of Electromagnetic Waves from a Thin Electric Antenna in a Planar Waveguide with Inhomogeneous Filling

We consider the problem of radiation of electromagnetic waves from a thin electric antenna located in a planar waveguide with perfectly conducting walls filled with an inhomogeneous dielectric. Cases where the antenna is fed by a time-harmonic e.m.f. and a bell-shaped impulse signal are analyzed. The current distribution along the antenna, its input admittance, the longitudinal component of the electric field, and the total complex power of the antenna are calculated numerically. We compare the antenna characteristics for waveguides with homogeneous and inhomogeneous filling.     

Axisymmetric Waves in Re-Entrant Cavities

We employ a well-established method to determine the dispersion properties of transverse magnetic and transverse electric waves in re-entrant cavities. We assume that the waveguide structure consists of a large number of identical cavities in order that the Floquet theorem could be applied to describe the electromagnetic field in an empty cylinder. Furthermore, we describe the electromagnetic field in each cavity region by an eigenfunction expansion for standing waves. Inferring boundary conditions leads to a system of two infinite sets of equations, which is solved numerically by truncation. A numerical code has been developed to calculate the dispersion relation and the electromagnetic field components. Numerical results are presented for several waveguide geometries, including the case of the real gyrotron beam-tunnel geometry. A comparison with already established codes is made.     

Transient radiation in an anisotropic magnetodielectric plate in a waveguide

We have considered transient radiation of a charged particle in an anisotropic magnetodielectric plate placed into a regular waveguide. It is assumed that the charged particle passes through the plate moving at a constant velocity perpendicularly to the waveguide axis. Wave equations and analytical expressions for transverse electric (TE) and transverse magnetic (TM) fields in different regions of the waveguide have been obtained. Energies of transient radiation of the moving particle have been calculated. The properties of transient radiation and Vavilov–Cherenkov radiation have been analyzed for the case of a rectangular waveguide. Energies of transient radiation have been calculated for the case of a “thin” plate in the waveguide, when the wavelength in the plate is much greater than the length of the plate.     

Energy Losses of a Charged Particle due to Excitation of Helicons in Plasma-Like Media

We study the energy lost by a particle moving along the helical line in a static magnetic field due to Vavilov–Cherenkov radiation of volume and surface helicons. It is found that the energy losses related to excitation of volume helicons are equivalent to the energy losses of a magnetic moment created due to the charge rotation. The magnetic moment moves at a constant velocity along the magnetic field. It is shown that collisionless damping of volume helicons in plasmas is based on the Cherenkov radiation of magnetic moment. Radiation of surface helicons by a particle does not correspond to the energy losses of a moving magnetic moment. This is related to the fact that not only magnetic (H) waves but also electric (E) waves contribute to the excitation of surface helicons, which leads to an increase in the energy losses of a particle.     

Frequency upshifting of electromagnetic radiation via obliqueincidence on an ionization front

Frequency upshifting of electromagnetic radiation impinging on a relativistically moving ionization front is theoretically investigated. Unlike previous works in this field treating the case of normal incidence and qualitatively similar case of oblique incidence of a transverse electric polarized wave, oblique incidence of a transverse magnetic polarized wave on the front is considered. The peculiarities of the case under consideration are connected with the generation of Langmuir waves behind the front and Brewster's phenomenon. We present a complete analysis of the incident wave transformation including analysis of the frequencies and amplitudes of the waves excited ahead of and behind the front. Special emphasis is made on energy transformation in the case when a wave packet is incident on the front. In particular, we show that even for negligible angles of incidence, energy losses via transformation into Langmuir waves may be very high (up to ~60%). In general, generation of Langmuir waves may play a significant role in the plasma-based radiation sources with relativistic ionization fronts     

Axion electrodynamics in a waveguide

The interaction of axion and electromagnetic waves is studied in the presence of a magnetic field threading a waveguide. This interaction, which vanishes in free space, is found to induce transverse magnetic waves with frequency spectra associated with transverse electric waves in the absence of the axion.     

On generation of electromagnetic waves in the terahertz frequency range in a multilayered open dielectric waveguide

We show that it is possible to produce terahertz wave generation in an open waveguide, which includes a multilayer dielectric plate. The plate consists of two dielectric layers with a corrugated interface. Electrons, drifting in the potential well, interact with the non-uniform electric field which is induced near the dielectric interface by the natural wave of the waveguide. The corrugated period and parameters of the electronic system are chosen in order to ensure the most effective interaction of electrons with a wave. Generation of electromagnetic waves is achieved by converting the electrons? energy into the electromagnetic wave energy.     

圆棒介质波导的电磁波传播特性

通过简单的数学分析,推导圆棒介质波导的导模传播条件及特征方程,讨论电磁波在圆棒介质波导中的传播特性。     

Field Structure in the Cross Section of a Ferrite Inhomogeneous Anisotropic Insert of a Rectangular Waveguide

We develop a physico-mathematical model describing excitation and distribution of electromagnetic waves in an anisotropic waveguide or resonator in the three-dimensional case. We develop a theoretical approach for discretization of the Maxwell equations in an arbitrary medium in the presence of bounding walls of a waveguide or resonator. The resulting system of linear algebraic equations for the electric-field components in an inhomogeneous anisotropic medium is solved by the method of biconjugate gradient. The results of calculating the electric field lines in the cross section of an anisotropic insert of a rectangular waveguide are presented.     

Magnetic-Type Waves in a Tapered Waveguide of Subwavelength Cross Section

The characteristics of electromagnetic waves in a narrowing waveguide are investigated. A method for field analysis is developed based on the application of transverse modes parametrically dependent on the longitudinal coordinate. For a circular cross section waveguide, a system of equations for the wave amplitudes is obtained, the waves being coupled owing to a variable tilt of the walls. It is shown that in the adiabatic approximation, there exist independent eigenwaves whose structure reflects the field energy density variation due to the waveguide radius variation. A detailed analytical and numerical investigation of these fields has been carried out for a waveguide with a special profile of hypergeometric type. The applicability of the adiabatic approximation is studied and conversion of the fundamental mode into higher-order modes is assessed. The amplitudes of the higher-order modes are obtained using the Green function for ordinary differential equations. The region of the waveguide parameters is found where the higher-order mode amplitudes are not great and the adiabatic approximation is highly accurate. The dependence of the transmittance of a semi-infinite waveguide on the input radiation characteristics is obtained. It is established that the field amplitudes at the waveguide output strongly depend on the wavelength of the input radiation, on its transverse structure, and the waveguide profile steepness. The greatest output fields take place in the case of an abrupt dependence of the waveguide radius on the longitudinal coordinate.     

Circular polarized coherent thermal radiation from semiconductor layers in an external magnetic field

We investigated, both theoretically and experimentally, the polarization properties of coherent thermal radiation from thin semiconductor planar layers in a weak external magnetic field. For the Faraday configuration, it is shown that the spectrum of thermal radiation is a superposition of two oscillating spectra which correspond to radiation of electromagnetic waves with right- and left-hand circular polarization.     

Guided modes in asymmetric graphene waveguides

An asymmetric quantum well in graphene can act as a slab waveguide for electron waves in a manner analogous to the electromagnetic waves in dielectrics. Guided modes and the probability current density are analyzed in the graphene electron waveguide induced by asymmetric electrostatic potential. The modes in an asymmetric graphene waveguide include guided modes, “cover modes”, “substrate modes” and “radiation modes”. The conditions for a guided mode are quantified. It is found that the fundamental mode is absent when both the Klein tunneling and classical motion are present. The confinement of electrons for lower order mode is stronger than for higher order mode. We hope that these characteristics in asymmetric graphene waveguide can provide potential applications in graphene-based waveguide devices.     

Interference of guiding modes in “traffic” circle waveguides composed of dielectric spherical particles

The interference of guiding polariton modes propagating through the waveguide composed of dielectric spherical particles forming a “traffic” circle docked by two linear entrance and exit chains is investigated. The dependence of intensity of the polariton wave on the position of the particle on the circle was studied using the multisphere Mie scattering formalism. We show that, if the frequency of light belongs to the pass-band of the circular part of this waveguide, the electromagnetic waves may be considered as two optical beams running along the circle in opposite directions and interfering with each other. Indeed, the obtained intensity behavior can be represented as a simple superposition of two waves propagating along the circle in opposite directions. The applications of this interference are discussed.     

左手材料薄板波导中模式之间的正交关系

基于电磁场理论,采用直接计算的方法证明了左手材料薄板波导中各个模式是相互正交的,即不同传播模之间、传播模与辐射模以及不同辐射模之间是相互正交的.这为研究左手材料薄板波导中的模式耦合奠定了基础. 关键词： 左手材料 薄板波导 模式 正交关系     

Natural Electromagnetic Waves in a Circular Waveguide with a Chiral and a Dielectric Layer

Based on particular solutions of a system of wave equations which describe electromagnetic processes in an unbounded biisotropic medium and are represented in the form of generalized power series, a dispersion equation is obtained for a two-layer circular waveguide with a chiral and a dielectric layer. The solution of the dispersion equation is analyzed for some types of natural waves.     

A polarization splitter based on slow light effect in a left-handed material waveguide

We propose a polarization splitter (PS) based on the slow light effect in a three-layer waveguide that consists of left-handed material (LHM) and dielectric layers with no birefringence. Transverse electric (TE) and transverse magnetic (TM) waves can be split by the intrinsic configuration of permittivity and permeability of LHM and dielectric layers. Simulation results are given to discuss the influence of electromagnetic parameters on the properties of our PS, and the capture and release of TE or TM waves are also realized in our PS which provides a flexible method to modulate the switching of different polarization waves.     

Specific features of the propagation of electromagnetic waves in a waveguiding structure with superconducting film and metamaterial

The propagation of electromagnetic waves in a rectangular waveguide containing layers of common dielectric and metamaterial with a negative refractive index separated by a thin film of a superconductor of the second type in the mixed state is considered. The possibility of amplifiying waves at frequencies lower than the cutoff energy due to the energy of an Abrikosov vortex lattice moving in the superconductor is demonstrated.     

Vavilov-Cherenkov effect in a chiral waveguide

The Vavilov-Cherenkov radiation appearing in a circular regular ideal waveguide with a chiral medium is considered. The features of the emission spectrum excited by a charge moving along the waveguide axis are investigated. Expressions for the energy loss of a moving charge are obtained. Zh. Tekh. Fiz. 69, 69–71 (March 1999)     

Interaction of counterpropagating electromagnetic waves in an absorbing plate inside a waveguide

The interaction of two counterpropagating coherent transverse electric and transverse magnetic electromagnetic waves in an absorbing plate that is placed in a waveguide with an arbitrary transverse cross section is analyzed. It is assumed that the waves with different initial phases are incident on the plate boundaries from two sides. An analytical expression for the interference transmission coefficient with respect to power is derived. Several physical features of the tunneling interference in the plate are revealed. It is demonstrated that a scenario in which an electromagnetic energy flux exists on the left-hand side of the plate and vanishes on the right-hand side or vice versa is possible at certain relations of the initial phases and amplitudes of the counterpropagating waves.     

Diffraction of guided waves by the end face of a dielectric slab waveguide terminated with a finite conductive strip

The diffraction of guided waves by the end face of a dielectric slab waveguide short circuited with a finite conductive strip is analyzed. An integral equation technique is employed to formulate the corresponding boundary problem. The unknown term in this integral equations is the electric field E(x) on the terminal plane of the waveguide. The homogeneous term is determined from the incident guided wave. A method of moments technique is employed to compute approximately the electric field E(x) by using Laguerre functions as describing and testing functions. The reflection coefficients of the guided waves are computed by using the approximate expression of the E(x) field. Numerical results are given for several guide and conductor plate dimensions.