The theory of solitons in a medium whose dispersion and nonlinearity are described by the Duffing equation, is discussed. A modified Korteweg-de Fries equation is derived for signals comprising a small number of oscillations under the envelope. The soliton and breather propagation is investigated. It is shown that as the number of periods increases, the breather turns into the envelope soliton. The process of formation and propagation of slow solitons in a cubically-nonlinear medium with a limited passband is considered for the case of two real physical systems (the waveguide and periodic structure}. Exact analytical expressions for the soliton shape are obtained and the region of their existence is indicated. The conditions for excitation of a nonpropagating soliton are discussed.
Show AbstractMathematical models of RF electromagnetic fields in a three-dimensional statement are described. The specific features of solving three-dimensional problems are discussed, including problems of increasing the accuracy and elimination of false solutions. Information is given on programs compiled in other countries for solving three-dimensional spectral problems; their comparative characteristics are presented. The algorithms and results of a numerical modeling for the ISFEL3D program compiled in Russia are described.
Show AbstractA generator of coherent short-wave radiation, called creditron, is proposed, which uses relativistic particles moving in trochoids in crossed electric and magnetic fields, and its physical foundations are described. It is shown that the wavelength of the generated radiation depends on the particle energy as in free electron lasers, but, in contrast to the latter, these installations can employ electron beams with wider energy scatter and lower density, i.e., beams, which arc currently available. The effect of the Coulomb field and the possible methods of particle focusing in such installations are considered.
Show AbstractAllowance for the space charge in relativistic microwave O-type devices encounters difficalties because of the absence of a rigorous theory of interaction of an ensemble of relativistic charged particles in nonuniform motion. A simplest model (thin relativistic electron beam (REB) without regard for thin metallic walls) has been employed to study electron grouping in the drift region and the amplification process in a traveling-wave tube of O-type (TWT-O) with irregular decelerating system. It is shown that: (a) During electron grouping, part of the REB energy is accumulated in the bunch in the form of interaction energy, which does not coincide with the relativistic potential energy and, for currents of the order of 200 A, attains 6 to 10% of the total REB energy; (b) The interaction energy leads to a TWT-O efficiency loss of the order of 10%; (c) The correction for the nonuniformity of the electron motion is insignificant, and, consequently, Lorentz' transformations can be used in the calculation of forces of the spatial charge in O-type devices.
Show AbstractThe induced emission of localized ensembles of electrons-oscillators in the free space has been studied. It has been found that the guiding effects take place during propagation of wave beams along the electron beams that play the role of open active waveguides. In the linear stage of the interaction the quasisurface modes are generated, and in the nonlinear stage, the wave beam broadens and the electromagnetic energy is emitted into the outer space. There occurs stochastic retardation of particles interacting with the ensemble of electromagnetic waves which propagate at various angles to the system axis, and this can increase the efficiency of the system as compared to the closed waveguides. The effects of superradiance have been found in the bunches of electrons-oscillators that form moving active resonators. The development of thresholdless instabilities leads to bunching of electrons and their coherent emission. This emission is quasimonochromatic in the intrinsic frame of reference and a multifrequency one in the laboratory frame. If the translational velocity of a bunch is close to the velocity of light, then the radiant power is concentrated predominantly in the short-wave component.
Show AbstractThe paper is concerned with the physical background of the operation of two-beam free-electron lasers (FELs). Both quasilinear and quadratic mechanisms of the superheterodyne amplification of electromagnetic waves are considered. It is asserted that, at the low- and medium-power levels, two-beam FELs will become the main amplifying devices in commercial systems operating in the submillimeter and IR wavelength ranges.
Show AbstractA survey is given of the state-of-the-art in numerical modeling of beams of charged particles propagating in electrodynamic systems and media. The features of various mathematical models of charged beams are described, the numerical methods of investigation are characterized, and the prospects for their development are discussed.
Show AbstractThe specific features of spectroscopy for the millimeter and submillimeter ranges of electromagnetic waves, the mechanisms of interaction with various media, and the peculiarities of the convenient spectroscopic techniques are considered. Examples are given of the application of millimeter and submillimeter wavelength spectroscopy in science and national economy.
Show AbstractOscillator devices employed in microwave radiometers are discussed. In order to stabilize the frequency and reduce the noise of the Gunn-effect oscillator, it is proposed to employ trapped-mode waveguide dielectric resonators, which are diffraction-excited in a rectangular waveguide either on a step-shaped H-inhomogeneity or on an E-inhomogeneity in the form of a parallelepiped with a gap along the wide wall of the waveguide. For calibration of the radiometers: wide-range noise sources have been developed, based on impact avalanche-and-transit time diodes (IMPATTD) and Shottky barrier diodes (SBD), which are highly stable with respect to the level of generation power. These sources employ the detected effects of the output signal self-modulation and self-thermostabilization.
Show AbstractThe experience in designing and fabrication of new types of solid-state millimeter band oscillators with quasi-optical dielectric resonators are summarized, and the underlying physical and engineering principles are considered. The authors describe the results of the experimental studies, and outline trends for further development.
Show AbstractThe application of millimeter-wave devices in transport, communications, and in equipment for radiometer sounding of the surface of land and ocean is discussed. The main engineering characteristics of the developed devices are generalized.
Show Abstract
