CAARN: Circular Autonomous Airborne Radar Node

his preprint proposes CAARN (Circular Autonomous Airborne Radar Node), a compactunmanned aircraft conceived around its sensing function rather than as a conventional dronecarrying a radar as an external payload. The architecture combines a circular or annularlifting body, distributed electronically scanned radar apertures, electro-optical/infrared sensing,cooperative-aircraft data such as ADS-B where legally available, inertial navigation, and edge AIfor real-time multi-sensor fusion. The primary objective is persistent three-dimensional airspaceawareness, detect-and-avoid support, traffic monitoring, infrastructure protection, emergencyresponse, and early warning. A military/dual-use configuration is considered only at the level ofsurveillance, tracking, resilience and command-and-control interoperability, without autonomousweapon employment.The concept is benchmarked against conventional ground radar, airborne detect-and-avoidradars, tethered overwatch drones, unmanned airborne early-warning systems, and large crewedAEW&C aircraft. The analysis indicates that the most credible near-term CAARN product isnot a miniaturized AWACS replacement, but a networkable airborne sensor node operating at lowaltitude or moderate altitude with a strong emphasis on low SWaP-C (size, weight, power andcost), autonomous health management, and cooperative multi-node fusion. A notional productioncost of approximately EUR 0.15–0.40 million per vehicle is considered plausible for a maturecivil/dual-use configuration, while a more capable long-endurance surveillance configurationcould reach EUR 0.4–1.0 million depending strongly on radar aperture, endurance, certificationand communications requirements. These values are engineering estimates rather than supplierquotations.