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Vol 60, No 3 (2017)
- Year: 2017
- Articles: 5
- URL: https://journals.rcsi.science/0735-2727/issue/view/10902
Article
Single sideband quadrature amplitude modulation
Abstract
Anew modulation scheme—single sideband quadrature amplitude modulation (SSB QAM) is proposed. This scheme allows to decrease the spectral width of the transferred signal by two times as opposed to the traditional quadrature amplitude modulation, while maintaining its spectral efficiency. This allows transmitting the modulated signal with the spectral width, which is equal to the spectral width of the modulating signal, and providing an energy gain of about 3 dB.
99-105
Tunable FSS simulation using WCIP method for multiband and dual polarized applications
Abstract
A novel multiband-operating and dual polarization frequency selective surface (FSS) for radomes applications for radar stealth is proposed. The design is based on an open metallic ring with coupled end strips. The proposed FSS rejects electromagnetic waves at frequencies 9.1, 10.8 and 11.5 GHz simultaneously with bandwidths of 900, 100 and 200 MHz, respectively, when the structure is excited by the x-polarized plane wave, and it rejects at one frequency 7.3 GHz with bandwidth of 1000 MHz, when the structure is excited by the y-polarized plane wave. Frequency tenability is provided by varying the length of the FSS coupled strips and the left edge of vertical U-shaped metallic strip composing the FSS structure. An enhancement of the x-polarized FSS bandwidth from 900 to 1500 MHz and from 200 and 100 to 500 MHz has been achieved. Simulation results obtained by the WCIP method were compared with the simulation results obtained by the COMSOL multiphysics software 4.3b and with the measurements. A good agreement of the results was observed.
106-112
Determination of amplitude levels of the piecewise constant signal by using polynomial approximation
Abstract
A new approach to determining the amplitude levels of piecewise constant signal has been proposed that is based on using its multiplicative model and solving the problem of polynomial approximation. In case of the absence of noise, the statement of polynomial approximation problem is based on the requirement of exact match of the current signal value with the amplitude value of one of its levels. In case of the presence of ordinary additive noise, the problem statement is based on the least squares criterion, while the solution of problem is presented in the analytical form. For the case of the presence of pulse-type noise, the problem statement is based on the minimum duration criterion, while the problem solution is achieved numerically by an appropriate functional minimization in unknown amplitudes of levels. The case of binary piecewise constant signal is considered in detail. The results of numerical simulation are presented for the cases, where the binary signal is distorted by ordinary additive noise with Gaussian distribution law and the pulse-type noise with the Cauchy distribution law.
113-122
Fluctuation characteristics of autodyne radars with frequency modulation
Abstract
A mathematical model of the autodyne radar with frequency modulation has been developed. The model is presented in the form of a self-excited oscillator with single-loop oscillating system adjusted in terms of frequency by varying the varicap capacitance. This model takes into account the impact of intrinsic radiation reflected from the object of location and inherent noises of the generator, as well as the power source noises. Basic expressions were derived for the calculation of the signal accompanying the spurious response of generator, components of the legitimate signal and the noise during the registration of autodyne response both in the power supply circuit and in terms of the variation of oscillation amplitude. Calculations of noise characteristics were carried out at small and large values of the feedback parameter. The phenomenon of periodic nonstationarity of noise levels at the autodyne generator output was detected in conditions of strong feedback. The results of calculations and experiments were obtained for the autodyne built on an 8 mm-band Gunn diode.
123-131
Stealthiness of analytical chaotic signals
Abstract
This paper considers an approach to constructing analytical chaotic sequences with statistical and dynamic characteristics that are close to the white noise characteristics. The notion of stealthiness and its measure were introduced for these sequences. Attractors of constructed sequences and their cross-correlation functions were studied. The results obtained in this paper can be used for enhancing the stealthiness of radio data transmission systems.
132-140