Ionospheric Effects on HF Radio Wave Propagation

Various radio wave instruments and technologies operating in the High Frequency (HF) radio band have been used for many decades and are reliant on or are affected by the Earth's ionosphere. These technologies include HF communications, environmental HF radar and sounders, sky-wave over-the-horizon radar and more recently line-of-sight HF radar used for space domain awareness. This chapter is concerned with how both the undisturbed and disturbed ionosphere affects HF radio wave propagation with a focus on the sky-wave problem. An extensive review of recent advances in this subject matter is provided in this chapter.