In order to locate the faint sources in the lightning discharge, an improved broadband VHF observation system is developed. Both the system configuration and locating algorithm are specially designed to locate weak radiation sources from background noise. The proposed system consists of seven broadband omnidirectional antennas in “L”shape and runs in continuous acquisition mode. An electromagnetic time reversal method designed in frequency domain is applied to locate the radiation sources. Two metrics have been introduced to distinguish between actual lightning sources and noise event. Numerical simulations and field calibration are carried out to test the system’s performance in locating weak sources. Moreover, the performance on spatial resolution, robustness, and the ability of multi-source localization are investigated. Finally, this system is applied to map the propagation of the upward positive leader (UPL) from a classical triggered lightning with time resolution 0.128 μs. The results prove that the proposed system could well depict the whole progression of UPL until its extinction, and the advantages of the proposed seven antennas array in retrieving weak radiations are presented in detail.
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