Vol 62, No 4 (2017)

The far field, the radiation pattern, and the radiation impedance of a traveling-wave antenna oriented in plasma along the external magnetic field in the resonance region of the whistler frequency band are studied. It is shown how the main characteristics of the antenna depend on its length and the current propagation constant along the antenna wire.

A method for generating the composite spread spectrum signals of satellite radio-navigation system based on linear equilibrium and nonequilibrium multiplexing of components is proposed to ensure the uniform amplitude envelope of a resultant signals. This makes it possible to solve the main problem of the given systems related to the low energy efficiency of signal amplification in the satellite radio receiver due to the substantial peak factor of an emitted signal.

The multidimensional constellations of quadrature amplitude modulation (QAM) signals are proposed. Each symbol incorporates the blocks of QAM signals not only carrying the same information content but also composed of the symbols of different higher order constellations (in contrast to the simple 1D modulation where each QAM symbol carries its intrinsic information). The multidimensional constellations of QAM signals are synthesized using the optimization algorithm based on the criteria for enhancing the energy or spectral efficiency of digital data transmission systems. The characteristics of interference immunity of the proposed signals are estimated with the help of analytical calculations and simulation. The relationships making it possible to consider faster-than-Nyquist signaling technology as a particular case of the multidimensional constellations of QAM signals are derived. It is demonstrated that the obtained signals provide an energy gain with respect to traditional 1D signals, in particular, ensure the operability at SNRs smaller than those inherent to binary phase-shift keying signals.

Active wireless networks with ultrawideband chaotic pulses used as the data carrier for wireless transmission are discussed. A universal transceiver module for nodes of active networks is proposed, designed, and studied. Various types of nodes based on this module are examined. The structure of active ultrawideband wireless networks and their operation principles are investigated. Examples of experimental networks based on the universal module are given, and their parameters are presented.

A set of coupled magnetoelastic equations is used to examine the problem concerning the establishment of free magnetization oscillations under the condition that dissipation is lacking in the magnetic system. The critical relationship between elastic damping parameters and the magnetoelasticity constant, which corresponds to the minimum in the dependence of magnetic damping on elastic one, is found. The bellshaped peak, on both sides of which the influence of an elastic system on the magnetic one diminishes, is detected in the dependence between the effective magnetic oscillation damping parameter and the elastic oscillation damping parameter. The observed phenomena is suggested to interpret using the model of two (magnetic and elastic) oscillators coupled through magnetoelastic interaction. The given model makes it possible to reveal four regimes of steady-state oscillations: weak damping with beats, strong damping without beats, weak damping without beats, and supercritical exponential growth. The mechanical similarity of observed phenomena is discussed, and recommendations needed to organize experiments are proposed.

Experiments on the ignition of electric discharge in air in quasi-optical microwave beam with subcritical field level are performed using a linear half-wavelength electromagnetic vibrator fixed above screen. It is demonstrated that the plasma of the induced electric charge at air pressures that exceed a critical level has a relatively high gas temperature providing the ignition of propane–air mixture.

A procedure for detection of the QRS complexes of electrocardiogram (ECG) signals for systems of long-term monitoring of the patient’s condition based on successive use of the band-pass filtering, the Hilbert transform, and an adaptive threshold algorithm is considered. The efficiency of different QRS-complex detectors has been investigated for model ECG signals in the presence of interferences of various nature and intensity. The efficiency of the proposed procedure has been additionally tested using various clinic records of ECG signals from the MIT Physionet database.

The circuit design and the topology of an 8-bit analog-to-digital converter (ADC) are presented. It is shown that the differential nonlinearity can be reduced by using three comparators and a majorizing element for formation of each bit of the thermometric code. Computer simulation and measurements of reference ADC chips fabricated using the UMC 180-nanometer CMOS technology confirmed the operability of the proposed design. A power consumption of 93 mW, an effective number of bits of 5.8, and a differential nonlinearity of 0.03 bits have been obtained