This thesis addresses the problem of passively determining the direction of a radio signal source where the measuring device does not emit a probe signal but obtains the information from the received signal. The primary objective was to establish the foundations for a system capable of reliably determining the direction of radio-controlled unmanned aerial vehicles, such as commercial drones.
In the theoretical part, various direction-finding methods (PoA, TDoA, AoA) are presented and the use of interferometry is justified as the most suitable approach. In the experimental part, the method was implemented using a two-channel software-defined radio PlutoSDR. The measurements were carried out indoors and outdoors. The programming of the receiver, the processing of the complex signal (I/Q samples), and the calculation of the phase differences are described in detail.
The results show that the performance of the system is strongly influenced by multipath propagation, which is a known limitation of all passive direction-finding methods. In closed environments with significant reflections, the dual-antenna receiver proved to be unreliable, whereas in open environments without major obstacles, the angle of arrival could be estimated with an accuracy of approximately ±9°. Potential improvements include increasing the number of receive channels and employing advanced algorithms that explicitly account for multipath effects.
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