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Measurements of surface waves radiated by a vertically polarized antenna over planar seawater at 5 MHz. comparison to planar Earth models

High Frequency propagation over the surface of the Earth or sea is a relevant subject today, especially for High-Frequency Surface Wave Radars (HFSWR) over the horizon. In this paper, we present measurements of Electric field propagating over sea water in HF Band compared to K.A. Norton, R.W.P. King and G. Millington's theories, thanks to a reliable measurement setup. The transmitter antennas are located on the coast while the receiver antenna is installed on a boat which sails at constant azimuth. The Electric field measurements are carried out with a shielded loop antenna and we measured the field strength attenuation versus distance between the transmitter and the boat along a sea water path. In order to take into account the media change (the coast and the sea water), Millington's solution has been added to King's and Norton's theories with the planar Earth model. At 5 MHz over the sea water, the environment of propagation is an attractive feature for the trans-horizon radar application. Indeed, the attenuation along the path in the planar model is similar to the attenuation in free space but over the horizon. The measurements performed at 5 MHz and the calculations are in a good agreement.