7 - Skywave radar

Abstract

This chapter focuses on skywave radar. Skywave radar is capable of sensing beyond the horizon because it makes use of the ionosphere to refract the radar wave propagated back to earth. A typical example includes the over-the-horizon radar (OTHR). Skywave radar utilizes the high-frequency (HF) band, specifically 3 to 30 MHz, as this band enables surface-to-surface radar to target distances well beyond the horizon. Skywave radar achieves its long ranges by using the ionosphere as a gigantic mirror. The conventional microwave radar operates on the line-of-sight principle and propagates through the ionosphere at frequencies of 0.2-40 GHz, whereas the HF band utilized by the OTHR, which is lower than that operated by the microwave radar, interacts with the ionosphere in a way that can be exploited to provide radar coverage at variable distances. Another difference between skywave and microwave radars is the need to adapt the signal waveform and frequency of the skywave radar to the environment.