This draft European Defence Fund (EDF) 2026 Lump Sum Development Action topic targets new capabilities in over-the-horizon (OTH) sensing to strengthen EU strategic surveillance and situational awareness. EU surveillance requirements (as referenced in the EU Capability Development Plan) underline the need to increase situational awareness through long-range radar systems. High-frequency (HF) OTH radars can provide long-range detection by exploiting HF propagation: sky-waves reflected by the ionosphere can enable coverage over thousands of kilometres, while surface-waves can follow the Earth’s curvature for a few hundred kilometres. However, sky-wave radars have an inherent blind area (skip distance): sky-waves typically return to Earth beyond roughly 1,000 km, leaving shorter-range areas without illumination. This makes single national installations most suitable for geographically large countries, while geographically confined countries can only achieve a collaborative air and maritime picture over large areas through cooperation and networking of multiple OTH radar units.
The call aims to follow up and complement previous EDF activities in OTH sensing by developing technologies and an EU concept for a cognitive, scalable network of HF OTH sensors. Because OTH HF radars exist in multiple countries, the topic explicitly encourages investigating and implementing mixed passive-active networking, including (non-)cooperative passive radar modes, to increase coverage and detection in a networked environment (e.g., concepts similar to deployable multiband passive-active radar supported by stationary assets). The technological ambition is to integrate different HF infrastructures (transmitters and receivers) in collaborative active and passive modes, together with an ionospheric sounding network and cognitive spectrum management algorithms, to increase air and sea detection range for monitoring, early warning, and detection of challenging targets such as low-flying stealth aircraft.
More specifically, the topic targets improved detection, tracking and identification over wide areas with increased range and minimum latency to enhance situational awareness and operational superiority. It promotes combining both HF surface-wave radar (active, cooperative and non-cooperative passive) and HF sky-wave radar technologies so that each can contribute its strengths: wide long-range coverage (sky-wave) and gap-filling/shorter-range agility (surface-wave) within an adaptive network. The networked approach is also intended to improve detection and tracking of challenging targets, including hypersonic targets, slow surface targets, and low-observable (stealth) targets. The envisaged surveillance scope includes maritime and airspace coverage over different geographical areas, e.g., the Atlantic Ocean, the Mediterranean Sea and the Arctic Circle.
The scope requires proposals to conduct study, research and experimentation and to conclude with a proof-of-concept design that demonstrates the developed functionality and can act as a testbed for later prototype-scale projects. Demonstration may be partial or use reduced-functionality technology demonstrators (e.g., shorter antennas and reduced power). Modularity enabling future expansion towards a prototype is required, and initial tests in a network with existing equipment/infrastructures are viewed positively. EU-sourced technology should be incorporated to the greatest possible extent. The topic expects the involved technologies to advance from TRL 2–3 to TRL 5–6 and contributes to STEP objectives in deep and digital technologies.
Mandatory activities include feasibility and technical studies and design tasks, such as developing cognitive approaches for a network of HF-OTH active/passive radars (resource management at node and system level, including illuminators of opportunity and specific modes such as COMINT/SIGINT/ELINT), feasibility of an AI/ML framework for big-data experimentation, intelligent electromagnetic spectrum management, multistatic tracking and adaptive filtering algorithms, and synchronisation over long distances (including immediate synchronisation using sky-wave signals and operation in GNSS-denied environments). Design tasks include the on-site multi-sensor tracker and fusion concepts, AI/ML framework specifications, and architecture for radio-frequency synchronisation. Additional (recommended) work covers minimalistic OTH-B concept studies, use of existing HF sources, propagation/noise modelling with real-time ionospheric sensing, advanced signal processing (clutter mitigation, localisation, hybrid modes, MIMO, multipath and Doppler fading), very-long-baseline issues, distributed modular receiver station design (SDR-oriented), deployable nodes, and design studies for minimalistic demonstrators. Optional activities include experimental prototypes for OTH-B sensors, HF radar, and passive HF radar using existing illumination sources.
Expected impacts include building participant Member States’ infrastructure and R&D capacity in OTH radar, enabling collaborative operational exploitation of active and passive OTH networks, integrating real-time ionospheric propagation models, identifying critical components, strengthening industry–RTO collaboration, supporting safe and secure operations in friendly and hostile environments under diverse geophysical conditions assisted by AI/ML, developing a robust longest-range surface-wave/sky-wave OTH-R system concept for EU surveillance, improving detection of low-observable targets, and contributing to reducing strategic dependencies of the Union.
Opening: 22.01.2026
Deadline(s): 29.09.2026
