Authors:I. A. Nosikov; P. F. Bessarab; M. V. Klimenko Pages: 1 - 12 Abstract: Fundamentals of the method of transverse displacements for calculating the HF radio-wave propagation paths are presented. The method is based on the direct variational principle for the optical path functional, but is not reduced to solving the Euler—Lagrange equations. Instead, the initial guess given by an ordered set of points is transformed successively into a ray path, while its endpoints corresponding to the positions of the transmitter and the receiver are kept fixed throughout the entire iteration process. The results of calculation by the method of transverse displacements are compared with known analytical solutions. The importance of using only transverse displacements of the ray path in the optimization procedure is also demonstrated. PubDate: 2016-07-19 DOI: 10.1007/s11141-016-9670-1 Issue No:Vol. 59, No. 1 (2016)

Authors:E. D.Tereshchenko; A. E. Sidorenko; V. F. Grigoryev; P. E.Tereshchenko Pages: 13 - 21 Abstract: We study the super-low-frequency field of a grounded horizontal electric dipole on a high-latitude submeridional path having a length of up to 1000 km. Unlike most of the earlier works, this paper considers the case of wave propagation along the dipole axis, where the main component of the magnetic field is radial. The frequency dispersion of the ground conductivity under the source, which determines the coefficient of excitation of the Earth—ionosphere waveguide, is found from the measurements of the field at a distance of three heights of the ionosphere. Typical parameters of propagation of super-low-frequency waves are refined allowing for specific features of the path used in the experiment. The significance of allowing for ground conductivity as the radiation propagates along low-conductivity regions is demonstrated. The regions where one of the magnetic-field components is predominant are calculated in a polar coordinate system linked to the source, as well as the regions where the both components should be allowed for. The theoretical possibility of determining the phase velocity of the wave based on the ratios of the magnetic-field components measured at longer lengths is noted. PubDate: 2016-07-19 DOI: 10.1007/s11141-016-9671-0 Issue No:Vol. 59, No. 1 (2016)

Authors:E. A. Shirokov; Yu. V. Chugunov Pages: 22 - 32 Abstract: We analyze the dynamics of the plasma-wave channels excited in magnetized plasmas in the whistler frequency range. A linear theory of excitation of a plasma waveguide by an external source is developed using the quasistatic approximation. Self-consistent spatio-temporal distributions of the electric field of quasipotential waves and plasma density, which are solutions of the nonlinear nonstationary problem of the ionizing self-channeling of waves in plasmas are found on the basis of the linear theory. PubDate: 2016-07-20 DOI: 10.1007/s11141-016-9672-z Issue No:Vol. 59, No. 1 (2016)

Authors:V. N. Manuilov; V. E. Semenov Pages: 33 - 42 Abstract: We solve analytically the problem about ion compensation for the space charge of a helical electron beam in a gyrotron operated in the long-pulse regime. Elementary processes, which take place during ionization of residual gas in the tube under typical pressures of 10−6–10−7 mm Hg, are considered. It is shown that distribution of the space charge is affected mainly by the electrons of the initial beam and slow-moving ions produced by ionization of the residual gas. Steady-state density of ions in the operating space of the gyrotron after the end of the transitional processes is found, as well as the electron density profile in the channel of electron beam transportation. The results obtained allow us to evaluate the pitch-factor variations caused by partial compensations for the potential “sagging” in the gyrotron cavity, thus being useful for analysis of starting currents, efficiency, and mode competition in high-power gyrotrons. PubDate: 2016-07-21 DOI: 10.1007/s11141-016-9673-y Issue No:Vol. 59, No. 1 (2016)

Authors:A. V. Dedov; V. G. Nazarov Pages: 43 - 47 Abstract: We study the electrical properties of multilayer radar absorbing materials obtained by adding nonwoven sheets of dielectric fibers with an intermediate layer of electrically conductive carbon fibers. Multilayer materials that absorb electromagnetic radiation in a wide frequency range are obtained by varying the content of the carbon fibers. The carbon-fiber content dependent mechanism of absorption of electromagnetic radiation by sheets and multilayer materials is considered. PubDate: 2016-07-20 DOI: 10.1007/s11141-016-9674-x Issue No:Vol. 59, No. 1 (2016)

Authors:K. N. Aleshin; V. V.Matrosov; V. D. Shalfeev Pages: 48 - 58 Abstract: We study collective dynamics of a small-sized chain of the unidirectionally coupled phase-locked loop. The conditions for the synchronous-regime existence are found, the asynchronous selfoscillation regimes and the transitions among them are studied, and the property of inheriting the structure of the parameter space of the chain when a new element is added to it is established. PubDate: 2016-07-25 DOI: 10.1007/s11141-016-9675-9 Issue No:Vol. 59, No. 1 (2016)

Authors:G. N. Bochkov; K. V. Gorokhov; A. V. Kolobkov Pages: 59 - 79 Abstract: We consider a method based on the generalized maximum-likelihood rule for solving the problem of reception of the signals with orthogonal frequency division multiplexing of their harmonic components (OFDM signals) in the time- and frequency-scattering channels. The coherent and incoherent demodulators effectively using the time scattering due to the fast fading of the signal are developed. Using computer simulation, we performed comparative analysis of the proposed algorithms and well-known signal-reception algorithms with equalizers. The proposed symbolby-symbol detector with decision feedback and restriction of the number of searched variants is shown to have the best bit-error-rate performance. It is shown that under conditions of the limited accuracy of estimating the communication-channel parameters, the incoherent OFDMsignal detectors with differential phase-shift keying can ensure a better bit-error-rate performance compared with the coherent OFDM-signal detectors with absolute phase-shift keying. PubDate: 2016-07-20 DOI: 10.1007/s11141-016-9676-8 Issue No:Vol. 59, No. 1 (2016)

Authors:V. L. Bakunin; G. G. Denisov; Yu. V. Novozhilova Pages: 893 - 904 Abstract: We study locking of the oscillation frequency of the operating TE28,12 mode by an external monochromatic signal in a multimode gyrotron operated at a frequency of 170 GHz in the switch-on regime close to the real one. Locking zones, i.e., regions of single-mode generation at the external-signal frequency are found on the “current—detuning” plane of parameters. It is shown that as the number of competing modes increases, the maximum achievable current decreases, and the locking zones contract at sufficiently high currents. PubDate: 2016-06-27 DOI: 10.1007/s11141-016-9663-0 Issue No:Vol. 58, No. 12 (2016)

Authors:V. E. Semenov; E. I. Rakova; M. Yu. Glyavin; G. S. Nusinovich Pages: 905 - 913 Abstract: The dynamics of the microwave breakdown in a gas is simulated numerically within a simple 1D model which takes into account such processes as the impact ionization of gas molecules, the attachment of electrons to neutral molecules, and plasma diffusion. Calculations are carried out for different spatial distributions of seed electrons with account for reflection of the incident electromagnetic wave from the plasma. The results reveal considerable dependence of the ionization wave evolution on the relation between the field frequency and gas pressure, as well as on the existence of extended rarefied halo of seed electrons. At relatively low gas pressures (or high field frequencies), the breakdown process is accompanied by the stationary ionization wave moving towards the incident electromagnetic wave. In the case of a high gas pressure (or a relatively low field frequency), the peculiarities of the breakdown are associated with the formation of repetitive jumps of the ionization front. PubDate: 2016-06-29 DOI: 10.1007/s11141-016-9664-z Issue No:Vol. 58, No. 12 (2016)

Authors:V. T. Ermolayev; I. S. Sorokin; A. G. Flaksman; A. V. Yastrebov Pages: 970 - 979 Abstract: We consider an adaptive multi-channel interference canceller, which ensures the minimum value of the average output power of interference. It is proposed to form the weight vector of such a canceller as the power-vector expansion. It is shown that this approach allows one to obtain an exact analytical solution for the optimal weight vector by using the procedure of the power-vector orthogonalization. In the case of a limited number of the input-process samples, the solution becomes ill-defined and its regularization is required. An effective regularization method, which ensures a high degree of the interference suppression and does not involve the procedure of inversion of the correlation matrix of interference, is proposed, which significantly reduces the computational cost of the weight-vector estimation. PubDate: 2016-06-27 DOI: 10.1007/s11141-016-9669-7 Issue No:Vol. 58, No. 12 (2016)

Authors:A. G. Sazontov; I. P. Smirnov; A. S. Chashchin Abstract: We consider the problem of determining the location of a coherent acoustic source in a shallowwater channel using a partially calibrated antenna array. To solve this problem, we develop a reduced-rank stable projection algorithm, which is the generalization of the RARE method to the case of signal reception under the conditions of incomplete information on the propagation medium. The results of experimental validation of the proposed approach, which show its efficiency under the conditions of an actual shallow-water area, are presented. PubDate: 2016-08-11 DOI: 10.1007/s11141-016-9678-6

Authors:S. N. Vlasov; S. V. Katin; E. V. Koposova; L. V. Lubyako; L. I. Prokofyev Abstract: We present a prototype of a quasioptical Mach—Zehnder interferometer with wave beam splitters in the form of reflective diffraction gratings. Characteristics of the diplexer are studied experimentally at frequencies of about 140 GHz. The measurement results are close to the calculated ones. PubDate: 2016-08-11 DOI: 10.1007/s11141-016-9683-9

Authors:A. N. Kuftin; V. N. Manuilov Abstract: We describe specific features of modeling numerically the operation of magnetron-injection guns, which form high-quality helical electron beams in gyrotrons operated in the short-wave part of the millimeter-wave band (at a wavelength of 1 mm). As an example, we consider the gun of a gyrotron having an operating frequency of 263 GHz designed for spectroscopic research. It is shown that there are good reasons to perform calculations and optimization of the magnetroninjection un in two steps. At the first step, a simplest two-dimensional model can be used, which allows only for the influence of the field of the electrodes and the intrinsic space charge of the beam on the beam parameters. At the second, final stage one should allow for such factors as roughness of the emitting surface and thermal velocities of electrons. The electron distribution function in oscillatory velocities and the coefficient of electron reflection from the magnetic mirror should be calculated. It is demonstrated that the magnetron-injection gun, which is optimized by the method presented, is sufficiently universal and can be operated both at the first and second cyclotron-frequency harmonics. This opens up the possibility of developing gyrotrons for spectroscopy applications at frequencies of 263 and 526 GHz, respectively, which are required for biological and medical research. PubDate: 2016-08-11 DOI: 10.1007/s11141-016-9682-x

Authors:A. G. Luchinin; L. S. Dolin Abstract: We study frequency dependences of the phase and group velocities of the photon-density waves in an anisotropic scattering turbid medium of the sea water type. It is shown that such a medium has an anomalous dispersion in relation to these waves, and their phase and group velocities are functions of the distance to a radiation source. The possibility of time focusing of the photondensity waves is considered for a linear frequency modulation of the radiated pulse. It is shown that full compression of the modulated signal is not achievable due to the frequency dependence of the refractive index of the photon-density wave. The degree of compression of the chirp signals with different parameters has been estimated. PubDate: 2016-08-11 DOI: 10.1007/s11141-016-9684-8

Authors:I. V. Pleshakov; P. S. Popov; Yu. I. Kuzmin; V. I. Dudkin Abstract: We consider a spin echo processor that uses a magnetically ordered material (ferrite) as a working substance. It is shown that it is possible to achieve suppression of the crosstalk (spurious signals) excited by radio-frequency pulses from different chains arriving at the system if the working substance is affected by sufficiently long magnetic field pulses. Thus, time-division multiplexing of the information processes can be carried out. PubDate: 2016-08-10 DOI: 10.1007/s11141-016-9686-6

Authors:V. E. Nazarov; S. B. Kiyashko Abstract: We study theoretically the nonlinear wave processes during excitation of a longitudinal harmonic wave in an unbounded medium and the rod resonator with inelastic hysteresis and saturation of the amplitude-dependent loss. The nonlinear-wave characteristics in such systems, namely, the amplitude-dependent loss, variation in the wave-propagation velocity, the resonant-frequency shift, and the higher-harmonic amplitudes are determined. The results of the theoretical and experimental studies of nonlinear effects in the rod resonator of annealed polycrystalline copper are compared. The effective parameters of the hysteretic nonlinearity of this metal are evaluated. PubDate: 2016-08-10 DOI: 10.1007/s11141-016-9680-z

Authors:V. L. Frolov; G. P. Komrakov; Ya. V. Glukhov; E. S. Andreeva; V. E. Kunitsyn; G. A. Kurbatov Abstract: We consider the experimental results obtained by studying the large-scale structure of the HF-disturbed ionospheric region. The experiments were performed using the SURA heating facility. The disturbed ionospheric region was sounded by signals radiated by GPS navigation satellite beacons as well as by signals of low-orbit satellites (radio tomography). The results of the experiments show that large-scale plasma density perturbations induced at altitudes higher than the F2 layer maximum can contribute significantly to the measured variations of the total electron density and can, with a certain arrangement of the reception points, be measured by the GPS sounding method. PubDate: 2016-08-10 DOI: 10.1007/s11141-016-9677-7

Authors:B. V. Sveshnikov; A. S.Bagdasaryan Abstract: We develop a self-consistent model allowing one to analyze the properties of the interdigital transducer of the surface acoustic waves as a symmetric five-layered waveguide on a piezoelectric substrate with three possible values of the phase velocity of the acoustic-wave propagation along the longitudinal axis of the system. The transcendental dispersion relation for describing the waves in such a system is derived and the method for its instructive graphic analysis is proposed. The condition under which only the fundamental transverse mode is excited in the waveguide is formulated. The method for calculating the normalized power and the transverse distribution of the field of the continuous-spectrum waves radiated from the considered waveguide is described. It is shown that the characteristic spatial scale of the longitudinal damping of the amplitude of this field at the waveguide center can be a qualitative estimate of the transverse-mode formation length. The efficiency of a new method for suppressing the higher-order transverse waveguide modes is demonstrated. PubDate: 2016-08-10 DOI: 10.1007/s11141-016-9679-5

Authors:S. V. Mikhaylovich; Yu.V. Fedorov Abstract: We perform a computational and analytical study of how the thickness of the barrier layer in nanoheterostructures and the gate-drain capacitance C
gd influence the microwave parameters (limiting frequency of current amplification and maximum generation frequency) and noise parameters (noise factor) of a field-effect AlGaN/GaN high electron mobility transistor. The results of complex measurements of the parameters of such transistors based on nanoheterostructures with a barrier layer thickness of 3.5–15.7 nm, which were performed within the framework of four technological routes in the range 0.1–67 GHz, are presented. It is shown that in order to reduce the noise ratio and improve the microwave parameters, it is necessary to optimize both the parameters of nanoheterostructures and the manufacturing techniques. In particular, the thickness of the barrier layer should be reduced, and the gate length should be chosen such as to maximize the product of the squared maximum current amplification frequency in the interior of the transistor and the output impedance between the drain and the source. Additionally, attention should be given to the shape of the gate to reduce the capacitance C
gd. Under certain conditions of manufacture of nitride field-effect HEMT, one can achieve a lower noise factor compared with the transistors based on arsenide nanoheterostructures. PubDate: 2016-08-10 DOI: 10.1007/s11141-016-9685-7

Authors:A. V. Shatsky Abstract: We consider the problem of the influence of diffraction effects on the result of measuring the absorption coefficient of ultrasound in weakly absorbing liquids by the pulse method. Diffraction attenuation of an ultrasonic signal in a measuring cell using solid-state delay lines is calculated. It is shown that the use of delay lines of the ultrasonic signal leads to a considerable distortion of the measured absorption coefficient in the low-frequency range from the true value and can either overestimate or underestimate the results. PubDate: 2016-08-09 DOI: 10.1007/s11141-016-9681-y