Zadorozhniy O. Parametric transformations in low-directional helicopter antennas

Thesis is devoted to the research and quantitative evaluation of signal distortions that arise in the communication radio channel of the helicopter. The purpose of the thesis is to develop theoretical and methodological foundations for the quantitative assessment impact of main rotor helicopter rotation on the quality of the data transmission channel from the helicopter board and on board. The mathematical model of pulsations antenna effective length is proposed in the paper. The pulsations of antenna effective length determine corresponding pattern pulsations of the antenna, which is installed on the conducting body of the helicopter. Using proposed mathematical model the influence of helicopter main rotor rotation on the spectral and energy characteristics different radio signals was investigated. A characteristic sign of distorted signals is the enrichment of their spectra by products of undesired amplitude modulation at frequency determined by the speed of rotation and by the number of rotor blades. The consequence of this effect is attenuation the average radiation power of the antenna and reduce the signal/noise ratio. The thesis also grounded graph-analytic method of quantitative evaluation of impact of the antenna pattern pulsations on the bit error ratio in the data transmission channel. This allowed estimating the maximum permissible level of the pattern pulsations for low-directed antenna.