Measurements of Vertically Polarized Electromagnetic Surface Waves Over a Calm Sea in HF Band. Comparison to Planar Earth Theories

Radio communication over Earth along mixed-paths in the HF band is a relevant subject today. In this communication, 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 transmitting antennas are located on the coast while the receiver antenna is installed on a boat steering a constant course. The electric field measurements are carried out with a 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. The measurements performed at three frequencies (10 MHz, 20 MHz and 30 MHz) and the calculations are in a good agreement. At 10 MHz, the “smoothly” attenuation is shown and is very well correlated with the theory. The EM field decrease as 1/d
²
has been clearly observed at 20 MHz and 30 MHz.