In High-Frequency (HF) Over The Horizon (OTH) radar, the space-time variations of the ionospheric channel, the external noise level (environment and man-made) as well as the transmission channel bandwidth limitations, are among the most critical and challenging aspects for the design and the operational management. Specifically, the knowledge of the ionosphere behaviour in a real time configuration is of primary importance because of the way it influences the frequency selection. This implies that a HF radar must have a high level of adaptability in order to deal with external constraints. For this purpose, a suitable frequency management system is needed. In this paper, a representation of the ionosphere propagation channel from a radar point of view is provided. Specifically, radio-electric parameters of the radar link are revisited by extending the concept of Maximum Usable Frequency (MUF), which is typically used in the communication field. The Ionospheric Propagation Chart (IPC) and Maximum Transmitted Frequency (MTF) are also introduced as new concepts. The present work is supported by simulation results.
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