Vol 69, No 5 (2024)

An antenna array with series excitation and its application as part of a radar with linear frequency modulation are considered. An analysis of an array consisting of Na parallel one-dimensional sub-arrays with series excitation forming a two-dimensional radiating array and coupling waveguides connecting the output of the n-th sub-array with the input of n+1 sub-array through 180° waveguide turns is presented. An approximate model of the antenna is proposed, which makes it possible to determine its main technical characteristics. Using the developed model, the time characteristics of the signal at the output of an ultrahigh frequency unit of a homodyne radar with linear frequency modulation are investigated. The dependences of the array quality indicators on the scattering parameters of elementary radiators and waveguide 180° turns are analyzed, and the technical requirements for them are formulated. It is shown that the radar provides scanning in the sector of azimuth angles ± 40° and ± 10° in the elevation with a frequency deviation in the 2 GHz band.

The results of numerical calculation of backscattering at large angles of incidence of TM-polarization plane waves on an extended metal surface of finite dimensions with a radio-absorbing coating based on the structure of an artificial magnetic conductor are presented. It is shown that a coating of this type with a thickness of 1...2 mm makes it possible to lower by 10...30 dB the first (from large angles) maximum on the angular dependence of backscattering at ultrahigh frequencies in a band of the order of an octave.

Two new classes of window functions, a special case of each of which is the Kaiser window taken as a sample, are proposed and investigated. In each class, we experimentally find suboptimal windows with the level of the maximum side lobe of the spectrum smaller than that of a sample with the same main lobe width and window duration.

Nonstationary oscillations in a system of two oscillators with a cubic connection arising in the problem of excitation of elastic vibrations in the scheme of a magnetostrictive transducer are considered. Three main oscillation modes were identified: regular beats, giant oscillations and asymmetric oscillations with a constant component. With respect to the mode of giant oscillations, it is shown that smooth oscillations are accompanied by frequent small fluctuations of small amplitude, the period of which is three orders of magnitude less than the period of the main oscillations. To interpret the observed phenomena, a model of dynamic potential is proposed, the movement of the minimum of which gives the main component of giant oscillations, and local fluctuations around the dynamic minimum provide a fine structure of frequent fluctuations.

The microwave coefficients of copper films with a thickness of 1...16 nm grown on a 1.8 nm germanium sublayer deposited on the surface of quartz glass substrates with a thickness of 4 mm are studied. The measurements have been carried out in a rectangular waveguide with a cross section of 23×10 mm² in the frequency range of 8.5...12.5 GHz. A smooth change in the microwave coefficients of the samples studied is detected in the range of copper film thicknesses of 2...16 nm. It is established that the critical percolation thickness of the copper films grown on germanium sublayer is in the range between 1 and 2 nm. A significant internal size effect is found in the films grown on Ge sublayer due to the scattering of conduction electrons mainly by intercrystalline boundaries. It is determined that the coefficient of reflection of conduction electrons by the intercrystalline boundaries of the copper films with Ge sublayer is more than three times higher than a similar coefficient in Cu films grown directly on the glass substrates.

The results of studies of the influence of uniaxial strain on the conductivity of the topological insulator TaSe3 are presented. Using the application of controlled elongation, the dependence of resistance at room temperature on the strain value was measured up to record strain values of ε = 2%. Using the elastic substrate bending technique, the measurements are extended towards the compressive strain. It was found that the dependence of resistance on deformation is described by the relation R(ε) = R₀ ехр(–аε) at а ≈ 10². The influence of uniaxial strain on the temperature dependences of conductivity using various methods of creating strain was studied. When creating a strain of more than 0.5 ± 0.1% by the method of controlled elongation, the material goes into a dielectric state in the temperature range from helium to 300 K; at deformations of more than 1% at temperatures of 50 ... 70 K, a maximum resistance appears, associated with partial relaxation of uniaxial deformation in the volume of the sample. It is shown that the use of the widely used technique of bending the substrate to create strain can lead to the appearance of artifacts in the temperature dependences of the conductivity of the samples.

Problem of immunity of the electronic devices under powerful electromagnetic emission as well as mechanism of device response at out-of-band emission influence are discussed. Parameters which characterize level of emission influence on device are indicated. The method of the empirical estimation of threshold level of these parameters, which characterize immunity of device under the influence of ultra-wideband (UWB) emission is proposed.

A new approach to the synthesis of a serial-to-parallel converter (SPC) based on the 0.25 μm GaAs D-mode pHEMT process is presented. Evolutionary algorithms application to solve SPC synthesis problem is shown. Solution, that have same structure as designer solution but with less power consumption, propagation delay and theoretically less total area is obtained. Its operability has been proved by comparison between simulated and measured data. Synthesis process takes up to 12 hours.