A. L. Dzvonkovskaya

The HF radar target detection is limited by casual active atmospheric, galactic and technogenic interference. The natural interference level at the lower part of HF-band is higher than thermal noise level and depends on daytime and season. Atmospheric interference with inverse-frequency levels is usually dominated at frequencies less than 10 MHz. Broadcasting and long-range communication systems with sky wave operating use the whole HF-band. Their rising activity at the lower part of HF-band during night-time is related to E layer disappearing and F1-F2 layer joining. The HF band load depends on geophysical environment that is periodical diurnal and seasonal variations in ionosphere and also solar activity. These factors influence to shift the bounds of used frequencies and their widths. It means that the HF band load density for radioelectronic systems varies in time. The frequency band distribution analysis shows that the special HF band allocation is not provided for HF radar. This leads to independent operating channel selection by HF radar while adapting to the current electromagnetic environment. Unlike the radioelectronic communication system adaptation using frequency grid, the HF radar adaptation is based on the continuous analysis of electromagnetic environment and operating channel choice with minimum casual interference level. There is a necessity to have at least from 3 to 5 free channels to provide the radar capability during the coherent integration time , and it takes into account that the selected channel existence time strongly depends on current electromagnetic environment. Operating status estimation of the preliminary selected free channels with the specified bandwidth in the set B and their existence time allow making a short-time channel utilization prediction for the coherent integration time forward to recommend them as operating frequency channels for HF radar detection capability.