Over-the-horizon radar (OTHR) systems operate in the high-frequency (HF) band (3–30 MHz) and achieve beyond-line-of-sight detection through either surface-wave or sky-wave propagation. Sky-wave OTHR exploits ionospheric refraction to extend surveillance coverage to ranges of approximately 3,500–4,000 km, whereas surface-wave OTHR relies on electromagnetic coupling with the sea surface to enable coastal monitoring over distances of roughly 350–400 km. OTHR continues to attract sustained interest due to its ability to provide persistent, wide-area, and cost-effective early-warning surveillance, particularly in regions where conventional microwave radars are impractical. Its dependence on relatively low-bandwidth HF signals and extensive ground-based signal processing also makes OTHR a compelling platform for the development and demonstration of advanced radar processing techniques.

This tutorial reviews the fundamental principles of OTHR operation within the HF environment, addressing both surface-wave and sky-wave modes. It emphasizes the contribution of surface-wave radar to maritime domain awareness and examines the performance of sky-wave radar in high-latitude environments. Key topics include system architecture, antenna design considerations, ray tracing methodologies, ionospheric dynamics, coordinate registration, ionospheric modelling, and frequency management. Illustrative examples are drawn from field trials and the deployment of a demonstrator OTHR system.

Presenters

Dr. Thayananthan Thayaparan is a Defence Scientist with Defence Research and Development Canada (DRDC) in Ottawa. His research interests are high frequency (HF) radio propagation, over the horizon radar (OTHR) applications, radar modelling and simulation, electron density and absorption models, space weather impacts, ionospheric perturbations, frequency management systems (FMS) for sky wave OTHR. His work includes synthetic aperture radar (SAR), inverse SAR (ISAR), noise radar, time frequency analysis for radar imaging and signal analysis, and radar micro Doppler techniques. He is a Fellow of the IET and serves on the editorial board of Remote Sensing. He has authored more than 220 publications, including journal papers, conference proceedings, technical reports, and three book chapters. He is also co author of the textbook Time Frequency Signal Analysis with Applications (Artech House) and a recipient of the IET Premium Award for Signal Processing.

Joshua Ruck is a Research Fellow and PhD Student in the Space Environment and Radio Engineering (SERENE) group at the University of Birmingham. His research focusses on High-Frequency skywave Over-the-Horizon Radar (OTHR), spanning modelling through to engineering systems. He is leading the engineering deployment of a multi-static OTHR demonstrator currently under construction. His PhD research is centred on the development of a coordinate registration and tracking system for the demonstrator radar, including the implementation of an inversion-based algorithm for simultaneous multi-static target localisation.

Dr. Reza Shahidi, PhD, SMIEEE, is a Professor at the Memorial University of Newfoundland in St. John’s, Canada. Before joining Memorial University in Dec. 2020, Dr. Shahidi worked as Signal Processing Lead at Rutter Technologies, Inc. where he designed and implemented many X-Band radar algorithms for marine target detection and oil spill detection, among other applications. He also served as Product Development Lead at Seamatica Aerospace in 2020 before joining Memorial. He is author/co-author of over 70 peer-reviewed journal and conference papers and holds a national NSERC Discovery Grant for the investigation of time-domain methods for ocean wave and current parameter extraction from the Government of Canada.