Near-field to far-field transformation applied to UHF antennas over lossy ground

This paper deals with a near-field to far-field transformation able to predict the radiation of UHF antennas located over a lossy ground. From in-situ near-field measurements, an equivalent set of dipole sources is obtained as a model of the characterized antenna. The paper details the main steps of the transformation and describes the specific experimental set-up designed for the application. Simple directional antennas (monopoles array) as well as more complex omnidirectional antennas (like a biconical antenna as a scaled-down model of a HF antenna) have been tested in realistic environments. This approach is very efficient for separating the contributions of the radiated waves: the sky wave and the surface wave.