Vol 69, No 4 (2024)

The question of the physical mechanism of electromagnetic radiation scattering by mesospheric (noctilucent) clouds is considered. A hypothesis has been expressed about the special electromagnetic characteristics of nanometer-sized ice particles that make up mesospheric clouds. Particle ice consists of a recently discovered crystalline modification of water — ice 0, formed by the condensation of vapor on dust particles at temperatures of –140…–23°C. Ice 0 is a ferroelectric, and upon contact with a dielectric, a layer with high electrical conductivity is formed. Due to plasmon resonance in nanosized layers, strong scattering of electromagnetic radiation occurs over a wide frequency range. This mechanism causes the glow of noctilucent clouds when illuminated by the radiation of the Sun.

The matrix method for measuring the radar characteristics of objects is examined. The method involves irradiating the object with a system of independent test fields, receiving the set of scattered fields, and performing posterior processing of the obtained results based on the superposition principle to determine the required radar characteristics of the object. An analysis of the information capabilities of the matrix method for measuring linear and nonlinear radar characteristics of objects is conducted, considering random errors in the registration of the amplitude and phase of the test signals. The variances of the desired linear and nonlinear radar characteristics of objects are determined, assuming a high signal-to-noise ratio in each test signal reception channel and maximum likelihood estimation of the amplitude and phase of the test signals. It is established that the matrix method for measuring radar characteristics of objects is functional under real conditions involving noise and interference.

The displacement of the bearing estimate in a direction finder with an adaptive noise compensator, its sensitivity and the sensitivity of a direction finder with an adaptive antenna array with restrictions have been studied depending on the antenna radiation pattern, the angular position of the signal and local interference, the correlation of distributed noise and spectral densities of signal power, noise and interference. A comparative analysis of the accuracy and sensitivity of these direction finders in the event of interference in the main lobe of the antenna pattern was carried out for a linear equidistant antenna array.

The problem of overlap of echo signals of adjacent probing cycles in synthetic aperture radars (SARs), called range ambiguity interference, or recurrent interference, is considered, which is usually solved by using orthogonal linear frequency modulated (chirp) and phase-code shift keyed (PCSK) in adjacent SAR probing cycles, which allows you to successfully suppress false signals from bright point targets from adjacent repetition periods. For SAR, various types of probing PCSK signals with a zero autocorrelation zone are considered, which make it possible to successfully solve the problem of suppressing recurrent interference from both point targets and extended objects. A comparative analysis of the correlation characteristics of orthogonal chirp and PCSK signals with various types of PCSK signals with a zero autocorrelation zone has been carried out.

To solve the problem of radar observations of small-sized space debris of natural and artificial origin, a multi-antenna distributed structure based on adaptive antenna arrays is proposed. A method for estimating noise errors of the phase method of low-Earth orbit space debris bearing for a channel of high-precision phase direction finding based on elements of a multi-antenna field is presented. The results obtained characterize the potential accuracy of the system. Based on the specified dispersion of phase fluctuations, the required signal-to-noise ratio at the input of the device is determined according to the proposed method.

A model of spatiotemporal summation of ultra-wideband chaotic radio pulses is proposed. The feasibility of using this model for analyzing scenarios of time-coherent radiation from independent sources of ultra-wideband chaotic radio pulses in wireless ultra-wideband systems is substantiated. Two scenarios are considered: where the distance between receiving point and emitters is much greater than the typical size of a group of emitters and where the receiving point is located between the emitters. Distributions of the total pulse energy in space for these scenarios are obtained.

The paper proposes a method for studying the variability of the subject’s heart rate based on the intellectual analysis of the pulse wave measured with remote photoplethysmography. The logically related stages of the formation of quadrature components based on the Hilbert transform of biomedical signals’ dynamics are presented. Within the framework of modern methods of intellectual analysis of non-stationary time series, realizations of adaptive estimates of instantaneous frequencies and periods of the heartbeat basic tone are obtained.

Dispersion properties of electroacoustic waves in the gap structure of two different piezoelectrics are considered. It is shown that in the considered structure PbTiO₃ – vacuum gap – BaTiO₃ in the presence of a difference of shear wave velocities in piezoelectrics there are no purely symmetric and antisymmetric modes, and the coefficients of the boundary localization of the shear wave will be significantly different.