Перегляд за Автор "Dodukh, O. M."

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    Improvement of Mathematical Models with Time-Shift of Two- and Tri-Fragment Signals with Non-Linear Frequency Modulation
    (КПІ ім. Ігоря Сікорського, 2023) Kostyria, O. O.; Hryzo, A. A.; Dodukh, O. M.; Nariezhnii, O. P.
    The use of signals with intra-pulse modulation in radar systems allows us to increase the duration of sounding pulses, and therefore the radiated energy with limitations on peak power. In the processing system, compression of the signal provides the necessary time difference, but leads to the appearance of side lobes. This, in turn, causes the “stretching” of the passive interference zone by range and worsens the potential for target detection. Therefore, reducing the level of the side lobes of the processed signal is an urgent task of radar. With regard to the maximum level of side lobes, signals with non-linear frequency modulation have advantages, but the models used for their mathematical description need to be clarified. The research carried out by the authors of the article and the obtained results of mathematical modelling explain the mechanism of frequency and phase jumps in signals with nonlinear frequency modulation, consisting of several linearly frequency modulated fragments. These results are obtained for the mathematical model of the current time, when the time of each subsequent fragment is counted from the end of the previous one. The article discusses mathematical models of two- and three-fragment signals with using different approach. The difference is that the start time of each successive linearly frequency modulated fragment is shifted to the origin, that is, the shifted time is used. The advantage of this approach is the absence of frequency jumps at the joints of fragments, but phase jumps at these moments of time still occur. Thus, there is a need to develop a mathematical apparatus for compensating of such jumps. An analysis of known publications conducted in the first section of the article shows that for mathematical models of shifted time, the issue of determining the magnitude of phase jumps at the joints of fragments and the mechanisms for their compensation were not considered. From this follows the task of research, which is formulated in the second section of the work. Mathematical calculations for determining the magnitude of phase jumps that occur in these mathematical models, as well as the results of checking the improved mathematical apparatus, are given in the third section of the work. Further research is planned to be directed at the features of using the developed mathematical models in solving applied problems in radar systems.
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    Mathematical Model of Two-Fragment Signal with Non-Linear Frequency Modulation in Current Period of Time
    (КПІ ім. Ігоря Сікорського, 2023) Kostyria, O. O.; Hryzo, A. A.; Dodukh, O. M.; Nariezhnii, O. P.
    Advantages of using frequency-modulated signals for locating objects are the possibility of using long-term probing pulses. Such signals provide the required radiated power while maintaining the desired discriminating power from range. One such signal that has found wide application is a signal with linear frequency modulation. An undesirable effect of the matched filtering of such a radio pulse is a sufficiently large level of side lobes of the compressed signal at the output of the processing device, the maximum level of which is approximately minus 13 dB. Such an effect may lead to an increase in the probability of false detection or masking of less powerful signals by side lobes of signals with greater power. One method of reducing the level of side lobes is the use of signals with non-linear frequency modulation. An example of such signals is a known two-fragment signal consisting of linearly-frequency modulated fragments in time. However, the mathematical models used to describe such a signal do not fully reflect the effects that occur at the moment of transition from one fragment of the signal to the second. These effects are manifested in a sudden change in frequency and phase, which leads to distortion of the signal spectrum, an increase in the level of the side lobes of the autocorrelation function and sharp changes in their level. Such effects have not been studied in known works, as evidenced by the results of the analysis of studies and publications given in the first section of the article. In the second section of the work, the research task is formulated. The third section of the work is devoted to the development of a mechanism for compensating for the manifestation of detected effects and its mathematical description, which is verified by modeling. Taking into account the detected effects, a new mathematical model of a non-linear frequency modulated signal has been developed. In contrast to those known in the proposed model, instantaneous frequency and phase jumps are compensated for, which occur at the moments when the frequency modulation rate changes during the transition from one signal fragment to another. Further studies should be focused on the peculiarities of compensation for the manifestation of detected effects for signals with a large number of fragments, as well as combinations of fragments with different types of modulation, as indicated in the conclusions on the work.