Volume 64, Nº 3 (2019)

An algorithm for filtering the coordinates of a fluctuating object in a security bistatic radio system with the use of a maximum a posteriori probability criterion is presented. Simulation of the algorithm and estimation of its efficiency are described. Plots of the rms error deviation are given.

Effect of load current and input and output capacitors on the frequency dependence of the ripple rejection ratio is studied for a classical linear voltage regulator based on an LM317L-N chip. In the absence of external capacitors, ripple rejection decreases with an increase in the load current at different input and output voltages. It is shown that a capacitor connected at the regulator output provides a significant increase in the ripple rejection ratio at frequencies of higher than 200 kHz and a capacitor connected in parallel to the regulating resistor in the feedback circuit provides an increase at frequencies of less than 300 kHz.

The paper is concerned with the distortion of a sharp leading edge of a quasi-monochromatic electromagnetic (light or radio) signal (wave packet) propagating in a medium with an absorption line (or band). It is shown that the frontal jump of the complex envelope of a radio signal propagates without changing its magnitude. Behind the leading edge, the signal level decreases with a rate increasing with the path length. As a result, the leading and trailing (if it exists) edges of the signal acquire tooth kinks, which become more and more acute with increasing path length. Such tooth kinks are formed not only at the points of discontinuity of the real amplitude of a signal but also at the points of discontinuity of its phase; therefore, the propagation of a phase-shift keyed radio signal in a resonantly absorbing medium is accompanied by its “self-disclosure”.

The propagation of the surface wave along the boundary between a hyperbolic magnetooptical single-axis metamaterial and an isotropic dielectric is considered. The dispersion equation of the surface wave and the distribution of the electric field in the system are found. It is shown that the surface wave of this system differs from other types of surface waves by the fact that the wave vector of the surface wave has not only the imaginary part but also a real part in the direction perpendicular to the interface. In addition, the surface wave in the hyperbolic magnetooptical single-axis metamaterial has a hybrid polarization. Therefore, there is only one surface wave for a given direction of the wave vector.

An electrodynamic limitation on the characteristics of antennas with a semi-infinite range as the limiting case of ultra-wideband (UWB) antennas is found. This limitation relates the directivity, the input reflection coefficient, the lowest operating frequency, and the overall size of the antenna and takes into account its geometric shape. An expression for estimating the lowest operating frequency of antennas with a given size and shape is obtained. Expressions for estimating the minimum achievable size and lowest operating frequency of rectangular printed UWB antennas with linear polarization are derived.

The excitation of an active phased antenna array through connecting a microwave self-oscillator to each transmitter has been investigated. A system of nonlinear differential equations has been used to describe the operation of self-oscillators in a mutual synchronization mode. Computer simulation of the system has been performed. An example of the calculation using a computer program and plotting the transient process of settling the self-oscillations is presented, which confirm the possibility of the existence of a mode of mutual synchronization of many self-oscillators.

In this paper, we studied the phonetic approach for voice processing. A method for automatic recognition of speech signals, in which each quasistationary segment is associated with a fuzzy set of phonemes, was developed. We proposed the operation of the probabilistic triangular norm for fuzzy sets corresponding to the input frame and the nearest reference phoneme. The developed method was experimentally shown to allow a 1.5–5% reduction in the probability of erroneous recognition in comparison with known analogues.

The polarization of eigenwaves and the total microwave magnetic field and microwave magnetization in a ferromagnetic metal plate is considered. It is established that, in the case of a thin plate with a thickness less than the skin depth, a significant role is played by the interference of the forward and backward eigenwaves. It is shown that both the microwave magnetization and the microwave magnetic field are elliptically polarized and the lengths of the semi-axes of the ellipses and their inclination, as well as the directions of the rotation of the corresponding vectors, are determined by the magnetization field. In particular, it is established that the polarization of the microwave field is different under the ferromagnetic resonance and ferromagnetic antiresonance conditions.

A W-band amplifier klystron has been designed based on a sheet electron beam and multigap cavities formed from a two-side comb slow-wave system segment. It has been shown via computer simulation that the proposed device has an output power higher than 1 kW, a gain of about 50 dB, an amplified frequency band of 0.4 GHz, and an efficiency of more than 10% at an essentially lower accelerating voltage compared with foreign analogous.

A new technology of nanostructuring and modification of the surfaces of silicon crystals of different types of conduction, using self-organized carbon mask coatings and highly anisotropic plasma-chemical etching is proposed. It is shown that the structures obtained make it possible to reduce the field emission excitation thresholds by several times and to increase the maximum field emission current densities by more than an order of magnitude in comparison with traditional technologies. It is established that the relation between the morphological and field emission characteristics of the obtained multi-tip cathode arrays is determined by the type of electrical conduction of the semiconductor and the total dipole moment of its surface. It is shown that the interpretation of the relation between them using the representations of the Fowler and Nordheim theory is not sufficient.

The paper presents a varicap-tunable fourth-order tunable microstrip bandpass filter with combined resonators: a U-shaped loop resonator and a resonator short-circuited at one end, which improved the symmetry of the frequency response while maintaining a wide rejection band inherent in comb filters with resonators short-circuited at one end. For the first time, the resonance equation for odd resonance frequencies of a U-shaped loop resonator with variable capacitance is obtained, which makes it possible to control the ratio of the first parasitic and the fundamental resonance frequencies of this resonator, f₁/f₀, on which the rejection band of the filter depends. An experimental sample of a filter, tunable in the frequency range of 225–400 MHz, is presented.

I–V characteristics and spectral photosensitivities of photodiodes based on epitaxially grown hydrides of metal-organic compounds (MOC-hydride epitaxy) of epitaxial structures with the In_0.67Ga_0.33As absorbing layer doped with Zn on the InP substrates are studied. The photodiodes are fabricated using the mesatechnology. The long-wavelength boundary of the spectral photosensitivity of diodes measured at half-maximum is 2.06 μm at room temperature. Photosensitivity spectra are studied in a temperature interval of 230–300 K.

The capacitance–voltage (CV) curves of metal–insulator–semiconductor (MIS) systems based on an HgCdTe nBn structure grown by molecular-beam epitaxy on GaAs(013) substrates were studied for the first time in a wide range of frequencies and temperatures. The electron concentration in the near-surface film layer was determined by capacitive measurements and is close to the indium dopant concentration. It was demonstrated that the CV characteristics of MIS systems have a high-frequency behavior in a wide range of measurement conditions, and the product of the differential resistance of the space-charge region and the electrode area in the strong inversion mode is as high as 40 kΩ cm². It was found that the capacitance of the MIS system in the accumulation mode decreases after irradiation at 0.91 μm. This effect may be attributed to the transformation of the band diagram of an abrupt heterojunction triggered by changes in the charge state of defects under irradiation.

Necessity of extension of the dynamic range of short-wavelength IR FPAs is substantiated. Conventional methods exhibit low efficiency, especially, in large-scale arrays with a pitch of no greater 15 μm. Integrating cells with individually tunable transfer function depending on the fragment brightness have the maximum efficiency with respect to the extension of the dynamic range (up to 100 dB). A simple (in topological implementation) and efficient method is proposed for extension of the dynamic range. The method is based on the individual self-tuning of integration time in each cell of the readout integrated circuit. Relatively high steepness and conversion linearity are maintained in integrating cells under moderate irradiation (up to 50–70% of the maximum signal) but the sensitivity is decreased in the cells that are close to saturation. The resulting linear–logarithmic transfer function provides extension of the dynamic range. Examples of images obtained with the extended dynamic range in the short-wavelength IR spectrum are presented.

Photoelectric characteristics of the focal plane arrays working in the visual-blind UV spectral range are studied. The dependences of the signal-to-noise ratio (SNR) on the integration time and the bias voltage on photodiodes and I–V characteristics of the photodiodes are measured. It is shown that ROIC noise dominates over the noise of photosensitive elements. The results indicate that the maximum integration time and bias voltage are needed to reach the best SNR. The method used to measure the I–V characteristics after hybridization with ROIC makes it possible to measure the dark currents of the individual photodiodes at typical values of 4 × 10^–15 A.

The results of the development and testing of a short-wave IR (0.9–1.7 μm) camera with the first Russian-produced 320 × 256 focal plane array (FPA) are detailed. This FPA was designed based on an InGaAs/InP heterostructure and has a pixel pitch of 30 μm and a suppressed temperature dependence of sensitivity. The primary components and parameters of the camera are discussed. Its advantages and possible applications both as a component of multispectral optoelectronic systems and as an independent device are reviewed.

The surface recombination rates for p-type HgCdTe layers with different dopant concentrations and trap densities N_t are calculated. It is shown that, at the given initial parameters, the surface recombination rate S_max lies in the range of 10–10⁴ cm/s. The current sensitivity for p-type HgCdTe is simulated using the dependence of quantum efficiency in the approximation of large lifetimes τ_n0 and large diffusion lengths L_n of minority charge carriers, taking into account the effect of the surface recombination rate.