Vol 68, No 6 (2023)

The Bessel beam-type asymptotic solutions of the three-dimensional Helmholtz equation, i.e., the solutions that have maxima in the vicinity of the -axis and are described by Bessel functions in the planes normal to it, are discussed. Since the Bessel functions slowly decrease at infinity, the energy of such solutions appears unlimited. Approaches to localizing such solutions by representing them in the form of the Maslov canonical operator on proper Lagrangian manifolds with simple caustics in the form of degenerate and nondegenerate folds are described. Efficient formulas for these solutions in the form of Bessel and Airy functions of a complex argument are obtained.

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated.

The problem of significant extension of the band of the transionospheric radio channel to the maximum possible values is solved to improve the efficiency of satellite communication systems. Hardware and software are created to suppress the group delay dispersion using methods of data mining for experimental diagnostics of a transionospheric communication line. Algorithms and tools for intelligent sensory diagnostics of wideband radio channels with adaptation to dispersion variability are developed. In the absence of adaptation, it is possible to create radio channels of undistorted transmission with a bandwidth ratio of no greater than 4.5%, while adaptation to dispersion variability makes it possible to increase the bandwidth ratio to 11.5%. The greatest bandwidth ratio (20–25%) for dispersion-free transmission can be achieved with the aid of adaptive inverse filtering of the channel frequency response in combination with such intelligent methods as equalization with error, machine learning of channel equalizer, and big data processing.

The results of the development of a prototype of the receiver of signals from global navigation satellite systems (GNSS) based on the U-blox ZED-F9P module are presented and a comparative analysis of its characteristics with professional GNSS receivers Trimble Alloy (KZN2 station of the IGS network) and JAVAD TRE-3L in the registration problem is performed. A qualitatively and quantitatively comparable behavior of the studied parameters for all types of GNSS receivers is noted.

A model of a radio line with fog, which is used to represent distortions of complex envelopes of digital signals because of the absorbing and dispersive properties of the propagation medium, has been considered. It is shown that with an increase in the frequency band of digital signals and with an increase in their  order of manipulation (when using frequency-efficient signals), the influence of these distortions leads to energy losses in relation to propagation in free space. The quantitative estimation of energy losses for the digital signals used in applications with multi-position phase, quadrature-amplitude, and amplitude-phase manipulations and for a radio line with fog with a variation of its parameters has been carried out. It has been shown that for signals with multiposition phase and amplitude-phase manipulations (the frequency efficiency coefficient of the signals is 4 bits/s/Hz), the energy losses reach 3.5 and 1.0 dB, respectively.

Specific features of the application of the spectral parameters of the received signal for the recognition of dangerous weather phenomena in a meteorological radar are considered. The advantages and disadvantages of existing methods are outlined. A new recognition method based on the estimation of the base of the input random process is proposed.