HEIMDALL - INVESTIGATING FEASIBILITY OF RESILIENT PASSIVE RADAR DETECTION OF COMMERCIAL UAV’S

Sammanfattning

The increasing availability of small commercial unmanned aerial vehicles (UAVs), introduces new challenges for the protection of critical infrastructure and restricted environments. Conventional active radar systems can detect such targets, but they require dedicated radio-frequency transmission and may be expensive, detectable, or unsuitable in emission restricted areas. There exists several research papers and investigation into the capabilities of a bi-static passive radar for the detection of these small UAVs. However, this thesis aims to investigate the implementation of reliability and redundancy in terms of receiver and illuminator hardware, with the purpose of passively detecting small UAV's The work was conducted in three experimental phases. Firstly, illuminators available at the location of our experimental phases were evaluated using a single-illuminator passive radar system. Furthermore, DVB-T and LTE signals were investigated and detections were evaluated. Secondly, a frequency hopping passive radar system was implemented to evaluate whether multiple illuminators could improve redundancy and reduce dependency on a single transmitter mitigating the single point of failure imposed by the single illuminator system. Thirdly, a frequency-stacking concept was investigated using two software defined radios to simultaneously process multiple illuminators. The experiments were performed on an airfield using a standardized flight path with a DJI Mini 4K drone. The system was evaluated using detection range, probability of detection, probability of false detection, and number of available illuminators. The results indicate that DVB-T illuminators are suitable for passive detection of small commercial UAVs, with reliable drone detections achieved at ranges exceeding the required threshold. The frequency hopping implementation demonstrated successful detection while increasing illuminator availability, thereby reducing the single point of failure associated with a single illuminator. LTE signals were also shown to be usable for detecting larger moving targets, although their suitability for UAV detection was limited by signal characteristics and implementation constraints. The frequency stacking experiment demonstrated the potential of a fail-operational passive radar system. The implemented frequency stacking system was limited by hardware constraints, reduced bandwidth and lack of phase coherence between SDRs. Nevertheless, the thesis demonstrates that resilient passive radar detection of commercial UAVs is feasible using illuminators of opportunity. The findings highlight the importance of coherent sampling, bandwidth, gain balance, non-coherent integration, and illuminator selection for future multi-illuminator passive radar systems. Future work should investigate fully coherent frequency stacking, improved LTE-aware processing, and position estimation through angle-of-arrival or elliptic intersection methods