Radiotehnika i èlektronika

A review and analysis of scientific papers published to date on various aspects of 6G is presented. The emphasis is on physical layer technologies, since they are the ones that largely form the basis and determine the potential of the future system. These include multiple access, multi-user multi-antenna systems, reconfigurable reflective surfaces, and modulation and channel coding techniques. In addition, promising application scenarios, new services and services, predicted requirements, concepts of 6G network architecture, the role of artificial intelligence and machine learning, as well as new frequency ranges are considered.

An algorithm is presented for the electrodynamic analysis of a two-dimensional waveguide slot array of finite dimensions. To solve the boundary value problem, the generalized scattering matrix method is used. The complex problem for a structure with large electrical dimensions is divided into two subproblems: wave scattering on one lattice element and the interaction of waves within the lattice. In accordance with this method, the electromagnetic field of a solitary lattice element is represented in the form of an expansion in incident and scattered spherical waves. The solution to the first subproblem is given by the scattering operator, which relates the amplitudes of the incident and scattered waves. The solution to the second subproblem yields an interaction matrix that relates the amplitudes of waves incident on the mth array element with the amplitudes of waves scattered by the nth element. Application of the scattering operator and interaction matrix to the analysed lattice leads to a system of linear algebraic equations for the amplitudes of the scattered waves. A non-periodic slot grating, focused in the Fresnel zone, containing up to a thousand elements is analysed. The obtained numerical results are in good agreement with the known behaviour of focused leaky wave gratings. Possible areas of application of the method are discussed.

Approximate asymptotic expressions are obtained for the partial radiating elements pattern and the active reflection coefficient of a large-sized quasi-periodic convex phased array antenna (PAA), using as a basis the results of a numerical solution for the electromagnetic field in a single PAA cell under periodic boundary conditions on the lateral surface of the cell. These expressions can be used to create mathematical software for modelling such phased arrays, taking into account the interaction of radiating elements, based on a combination of direct numerical methods, such as the finite element method, to analyse the field in a single cell of the phased array with the calculation of the characteristics of the phased array as a whole using analytical asymptotic expressions. Numerical results of applying the method are presented for calculating the characteristics of multi-element spherical phased array of slot radiating elements and conical phased array of slot and director radiating elements.

A statistical analysis of correlation fluctuations during information transmission using spectrum spreading based on continuous noise signals with spectral modulation was carried out. Discrete information is introduced as a result of the interference of the reference noise signal and the delayed noise signal, which is modulated by binary symbols of opposite sign. A numerical calculation of correlation and spectral characteristics during information transmission in a channel with additive Gaussian white noise was carried out. An asymptotic limitation has been discovered for the deviation of correlation fluctuations due to intra-system interference. The possibility of reducing fluctuations of the correlation effect when transmitting information based on continuous noise signals with time windows is shown.

A new generalized adaptive algorithm for learning to make statistical decisions for exponential families of distributions with a priori parametric uncertainty in conditions of small samples has been developed. A generalized decision rule is presented, obtained by estimating unknown parameters of distributions, as well as a decision rule that satisfies the necessary optimality conditions: constancy of the average probability of a type I error and unbiasedness. Specific decision procedures for partial distributions obtained from a generalized algorithm are considered. Numerical examples are given. The effectiveness of the developed optimal procedure for small samples is shown.

A low-noise bipolar differential dc amplifier was studied at temperatures of 300 and 77 K. It was shown that to ensure the best amplifier performance in terms of noise figure when the operating temperature decreases from 300 to 77 K, it is advisable to use the transistor in the mode of low currents not exceeding 2 mA. It has been established that lowering the operating temperature to 77 K leads to a decrease in the input resistance of the amplifier from a value of several kiloohms to 100 Ohms, the dynamic range increases from 80 to 85 dB, and the harmonic coefficient increases from 0.09% to 1%. In addition, lowering the operating temperature to 77 K has a significant effect on the noise properties of the amplifier: the spectral density of voltage noise decreases from 1 to 0.4 nV/Hz^1/2, the spectral density of current noise increases from 2.5 to 9 pA/Hz^1/2, while also The threshold frequencies of 1/f noise increase: for voltage from (0.1...10) to 20 Hz and for current from (10...100) to 1000 Hz. The possibility of using an amplifier for low-temperature measurements of samples with low input resistance is substantiated.