Radioelectronics and Communications Systems

Study of direction patterns of narrow-strip, sparsely filled pre-fractal gratings

2026-08-13T22:15:26+03:00

Characteristics of E-polarized wave scattering by systems of absolutely thin and conductive flat impedance strips, arranged according to the laws of construction of a perfect set with variable fractional dimension, have been investigated. The scattering problem statement is classically rigorous under certain assumptions. In this case, several classical methods, namely the method of integral equations and Lord Rayleigh’s asymptotic method, along with their modifications, have been used. Considerable attention is paid to two generalizations of the classical nowhere dense perfect set with dimension ln2/ln3, which significantly expand the possibilities for practical applications of such sets. A detailed mathematical analysis of the process of creating two different classes of nowhere dense perfect sets with variable fractional dimension is proposed. This analysis forms the basis for the creation of correct mathematical models of the scattering of plane electromagnetic waves by using strip systems. A simple asymptotic model of scattering of an E-polarized wave by narrow-strip sparsely filled gratings, ordered according to the laws of construction of perfect sets with variable fractional dimensions ln2/lnc (c > 2) and ln3/lnc (c > 3), has been developed. This model forms the basis for developing algorithms to calculate the direction patterns of certain classes of strip gratings ordered according to new mathematical laws. The study and modeling performed by the author can be useful for improving the performance quality of electronic devices that use antenna gratings.

Transmission line meander dual-mode resonators and bandpass filters

2026-08-13T22:27:05+03:00

In this paper, the problem of synthesizing and studying the properties of transmission line dual-mode resonators characterized by a single dimension is solved for the first time. The initial samples for the synthesis are stepped-impedance resonators (SIR) with different numbers of composite sections N, and characteristic impedances Z_0i, i = 1, 2, …, N. Four dual-mode resonators were synthesized, which represent a meander with alternating sections of high Z_0max and low Z_0min characteristic impedance. In two resonators, dual-mode oscillation arises from the mutual convergence of the resonant frequencies f₀₁ and f₀₂, forming a meander with three sections. The other two resonators represent a meander with five sections. In these resonators, dual-mode oscillation arises from the convergence of the resonant frequencies f₀₂ and f₀₃, enabling operation at higher frequencies without reducing their length. Both ends of these resonators can be either open-circuited or short-circuited. A simple analytical dependence of the even f_e and odd f_o modes on the parameter m = Z_0max/Z_0min of synthesized meander dual-mode resonators was established. The larger the parameter m, the closer f_e and f_o modes are. Their convergence can be as low as 4%. This dependence made it possible to express the coupling coefficient K between the even f_e and odd f_o modes in terms of the parameter m, significantly simplifying the design of meander dual-mode bandpass filters (BPF). Design examples of such BPFs and their microstrip implementation are considered.

Magnetic resonance image data processing by periodogram method

2026-08-13T22:33:26+03:00

Magnetic resonance (MR) images are often influenced by undesirable noise that is combined with the relevant signal. Therefore, the resulting images may not provide the quality needed for their interpretation. This study proposes the periodogram as a nonparametric method for processing and reconstructing noise-affected MR images without prior knowledge of their spectral characteristics. Here, we simulate real-world image noise by artificially adding Gaussian noise. By transforming the corrupted MR image into the frequency domain, applying the Daniell periodogram, and performing an inverse transformation, the noise impact is reduced. The authors aim to evaluate the method’s potential applications and limitations for future use in MRI noise elimination, using the structural similarity index measure (SSIM), peak signal-to-noise ratio (PSNR), and fractal dimension (FD) metrics. The values of the said metrics of the denoised images largely correspond to the visual evaluation of the images.

Surrogate data for reducing time series reconstruction errors in caterpillar SSA

2026-08-13T22:38:44+03:00

The paper discusses the improvement of the caterpillar Singular Spectrum Analysis (SSA) method by using the surrogate data technology to increase the accuracy of time series reconstruction in the presence of additive noise. The use of the Attractor Trajectory Surrogates (ATS) algorithm to generate surrogate realizations is proposed, which effectively reduces residual noise in observations after processing with the caterpillar SSA method. The simulation results show that the use of surrogate data technology, combined with the caterpillar-SSA method, yields higher-quality time-series signal reconstruction than the baseline method, particularly under high-noise conditions. In the process of analyzing the quality of signal reconstruction, SG statistics was calculated, and the recovery coefficient was determined, which made it possible to obtain numerical values for the SG (Savit and Green) predictability index. These values were used to process the data, both by the baseline caterpillar SSA method and by its refined version using the ATS algorithm. The proposed approach is shown to reduce the dependence of time series restoration quality on the number of singular decomposition components, increase the stability of the results, and minimize the final noise level.

Express method for measuring cut-off frequency of acousto-optic delay line

2026-08-13T22:47:13+03:00

In the case of an acousto-optic delay line, the procedure for measuring the cut-off frequency is quite complex. This paper considers the influence of the light beam diameter and the acoustic wave propagation velocity in a photoelastic medium on the time constant of the transient response of the acousto-optic delay line. Based on the results obtained, an express method for measuring the cut-off frequency of an acousto-optic delay line is proposed. Some aspects of the practical application of this method are discussed. Relevant numerical examples are presented. The proposed express method for determining the cut-off frequency of the acousto-optic delay line has been experimentally verified, and the scatter in the obtained measurements has been estimated.