Том 69, № 2 (2024)

Numerical studies of the dispersion characteristics of cylindrical spiral lines have been carried out. One-dimensional and two-dimensional periodic lattices formed by such lines are also considered. The eigenvalue method was used in combination with periodic boundary conditions. The dispersion characteristics are calculated in the range of parameters for which the conditions of applicability of the known approximate numerical-analytical methods for analyzing spiral lines are not met. The dispersion characteristics of the first two eigen-waves in one-dimensional and two-dimensional periodic lattices of spirals are obtained for different values of phase shifts between lattice periods. It is shown that the main type of wave in them is a wave slowed down relative to the axes of the lines with the direction of rotation of the field vector determined by the direction of winding of the spiral.

Options have been developed for constructing circulant matrices of any M-sequence (MS) based on automorphic multiplicative groups of the extended Galois field, constructed using an irreducible primitive polynomial, on the basis of which the original MS is formed. The result of this approach is the identification of new methods for transforming MS circulant matrices to a matrix of Walsh functions, ordered by the powers of the antiderivative element of the field. It is shown for the first time that, depending on the initial conditions of the transformation, a set of any number of any cyclic shifts of the MP, shifted relative to each other by one symbol, can be transformed to any rows of the ordered matrix of Walsh functions, following one another. This circumstance makes it possible to simplify the MS synchronization algorithm for a known range of its cyclic shifts, especially in the case of large periods of its repetition, and also to reduce the computational complexity of the processing algorithm when working in a truncated basis of Walsh–Hadamard functions.

The influence of weight functions (WFs) of preliminary weighting on the quality of narrowband interference rejection based on direct and inverse discrete Fourier transforms has been studied. Classical and modern WFs are considered: Kravchenko, Kravchenko–Dolph–Chebyshev, Kravchenko–Gauss, Kravchenko–Bernstein–Rogozinsky. Quantitative estimates of efficiency were obtained – the coefficients of interference suppression and signal transmission, as well as their product – the total efficiency coefficient. Graphic examples of the behavior of the total efficiency coefficient depending on the interference frequency are shown. Estimates of the indicated quality indicators are presented when a fixed number of frequency samples are removed from the spectrum. The families of dependences of the probabilities of correctly performing a search for a spread spectrum signal on the “interference/signal” ratio when using modern WFs to weigh the implementations of an additive mixture of signal, interference and noise are presented. The significant advantage of modern WFs formed through combinations with Kravchenko functions in the problem of interference rejection has been demonstrated and confirmed.

A method is considered and an algorithm is developed that makes it possible to identify the layered structure of the propagation medium of a probing signal based on strip survey data from an interferometric side-scan sonar (ISSS) with antennas located in a vertical plane. Using the example of mathematical modeling of phase-difference measurements of ISSS for multilayer scattering planes, the capabilities of the proposed algorithm to determine their spatial position are demonstrated in the wave propagation medium. An analysis of the accuracy of calculating the position of scattering layers at heights (depths) and with different slopes was performed. The effectiveness of the method and algorithm for diagnosing the structure of layered media has been confirmed. The effectiveness of the method was tested on experimental data obtained using ISSS.

A method for theoretical analysis of “input-output” and “local oscillator-output” decouplings of three types of diode frequency converters is presented: balanced, double balanced, triple balanced. For two operating modes of the local oscillator – “non-intensive” and “intensive” – the dependences of the “input-output” decoupling of the balanced mixer on the load conductivity and on the amplitude of the local oscillator voltage were obtained. Theoretical analysis and modeling were carried out. It is shown that the error between the calculated results and the simulation results does not exceed 3 dB. Expressions are obtained for errors introduced by the technological spread of diode parameters, which make it possible to estimate the maximum achievable values of the mixer characteristics (transmission coefficient and port isolation). A method for analyzing the noise properties of mixers is presented, the output noise spectra are calculated for each of the circuit elements (input resistance, diodes and output resistance), and analytical expressions for noise coefficients are obtained. Theoretical noise figure estimates are confirmed by simulation results with an accuracy of 1 dB.

The kinetic characteristics of thermal frequency phonons in the region of helium temperatures in ceramic samples of the Ce_1–xGd_xO_2–y electrolyte solid solution have been studied. To explain the temperature dependence of the phonon mean free path, we used the previously performed calculations of the energy of vacancy formation in the anion sublattice of a solid solution of zirconium dioxide stabilized by yttrium ZrO₂:Y₂O₃ (YSZ) with a similar crystal structure. It is shown that in the Ce_1–xGd_xO_2–y system under study, the formation of structural defects associated with the presence of vacancies in the anion sublattice with energy Δ = 8.53 K is possible. It has been established that analysis of the temperature dependences of the YSZ heat capacity allows one to trace the degree of disorder (amorphization) of the solid solution depending on its level of stabilization.

Powerful picosecond optical pumping of the GaAs heterostructure layer causes the generation of stimulated picosecond emission in it. Due to its high intensity, the emission induces a Bragg grating of the electron population in the active region of the layer, making the latter an active photonic crystal. In the emission field, the inverse population of electrons oscillates with time, which should lead to spatiotemporal modulation of the emission and this population. It has been discovered that if the distance Y between the end of the heterostructure and the center of the active medium and the geometric parameters of the indicated modulation and movement of emission in the photonic crystal satisfy certain conditions, then dimensional resonance occurs - a maximum of modulation of the dependence of the energy of emission emerging from the end on Y and on pump energy appears locally.