Over the horizon radar

The tutorial provides an introduction to the fundamental principles of high frequency over-the-horizon (OTH) radar, including sky-wave and surface-wave systems as well as other bi-static HF radar architectures. The main challenges of operating in the HF environment are described and connected to motivate and explain the architecture and design of existing OTH radar systems. From this viewpoint, the most influential characteristics of the HF propagation medium, and those of different HF signals received by OTH radar, are described in detail. The essential properties of various radar sub-systems, including antenna, transmitter, and receiver, are also explained. This is followed by a description of the central features of conventional and adaptive signal processing methods in OTH radar. In addition to the theoretical aspects, the tutorial also contains numerous examples of practical results obtained from actual HF radar systems, new insights for the way ahead, and a comprehensive list of references. For this reason, it is expected to benefit scientists and engineers, either starting out in this field, or those wishing to gain a more complete understanding of the most critical OTH radar concepts.