Volume 70, Nº 1 (2025)

Beam forming network as a system of parallel coupled transmission lines with different coupling coefficients is proposed. The beam forming network feeds linear array that in its turn forms radiation pattern with sector shape. An eigenwave problem for an infinite system of infinite transmission lines is solved in frame of coupled wave theory. Also a problem of eigenwave excitation is solved in frame of the same theory. Relations describing wave amplitudes in output plane are obtained. Directivity multiplier of a linear radiating array that excited by the waves in the output plane is considered. The analysis demonstrates that application of new type beam forming network sufficiently improves radiation pattern shape in compare with radiation pattern of the array with beam forming network with identically coupled transmission lines.

An omnidirectional in one plane polyconical antenna with a torroidal gradient dielectric anisotropic Mikaelian lens, which is made in the form of a set of parallel coaxial disks made of polystyrene of various thicknesses, is proposed and studied using numerical modeling. As a result of the study and optimization of parameters, it was shown that the optimized polyconical antenna with the lens is matched and provides high efficiency in the 40:1 frequency band. The results of numerical modeling are confirmed by the results of measurements of the manufactured antenna prototype.

Numerical solutions of differential equations for a trigger on bipolar transistors in the presence of an external action are obtained. It is shown that the solutions have hysteresis properties. Differential equations for a single vibrator on bipolar transistors are derived and their numerical solutions are found.

The effect of coating GaAs monolithic integrated circuit with a benzocyclobutene dielectric layer and grounded copper shield is investigated. Using electromagnetic simulation up to 40 GHz, changes of RF characteristics of microstrip and coplanar transmission lines, a Marshand balun, and a bandpass filter due to coating are demonstrated. It is shown that from the performance variation viewpoint, the application of lines is preferred in GaAs monolithic integrated circuits used in 3D-integrated modules with such the coating.

Exact solutions of a non-relativistic non-monoenergetic beam are presented for flows with an elliptical cross-section and a spatial axis in a magnetic field for various laws of change of axial velocity.

The electrical resistance of the Mn₅Si₃ compound in magnetic fields up to 2 T at cryogenic temperatures in the range from 35 K to 90 K was studied. The characteristic temperatures of the magnetic phase transition T_N1 and T_N2 were determined based on the results of measuring the heat capacity at constant pressure C_P, magnetization M and specific electrical resistance ρ. It was shown that the behavior of the ρ(T) curves differs depending on the measurement conditions and protocol. Based on the results of measuring the magnetocaloric properties in strong magnetic fields up to 10 T at cryogenic temperatures in the range from 25 to 125 K, both the inverse and conventional magnetocaloric effects were observed. The maximum value of the inverse magnetocaloric effect was ∆T_ad = –1.1 K at an initial temperature T₀ = 50 K in a magnetic field of 10 T. Conventional magnetocaloric effect with a maximum value of ∆T_ad = +0.9 K is observed at T₀ = 62.5 K in a field of 10 T. A local exponent of field distribution of entropy n is determined, the value of which n > 2 confirms the type and existence of a first-order phase transition.

The influence of internal local and external demagnetization fields on the critical current density of inter-doublet Josephson weak bonds J_c of high-temperature superconducting YBCO samples is investigated using the oscillation differential technique of local approximation. In the zero-field and zero-field cooling with flux accumulation regimes for samples with different J_c and twin sizes d, the demagnetization fields of samples H_D1 and H_D2 have been measured. The values of: d; thermodynamic first critical magnetic fields of twins H_ic1; twin demagnetization fields H_{D tr}; density of intra-twin effective critical currents J_{c ef}; critical pinning currents J_{c p} and shielding Meissner critical currents J_{c M} are determined. It is shown that at H_ic1 fields the twins of large sizes “disintegrate” into a group of smaller twins with close demagnetizing factors. It is found that an increase in J_{c M}, J_{c ef}, and a decrease in d lead, on the one hand, to a decrease in J_c due to an increase in the demagnetization field of the sample H_D and H_{D tr} created by J_{c ef} and J_{c M}, and, on the other hand, to an increase in J_{c ef} and J_{c M} due to a decrease in d.

The Rate-Splitting Multiple Access (RSMA) method for multi-antenna communication systems is described. The sequence of operations for RSMA signal formation and processing is presented. RSMA usage scenarios in communication systems are considered, and the efficiency of this method is substantiated. Capacity estimates of the RSMA method are obtained in comparison with other multiple access methods. Numerical modeling of the average capacity per user is conducted using the QuaDRiGa tool. It is shown that RSMA achieves higher capacity compared to other multiple access methods used in multi-antenna communication systems.