Enhance efficiency of High Frequency antennas using lossy metamaterials

It is well-known that low frequency waves are propagated beyond the Line-of-Sight (LoS) [1]. In the High Frequency (HF) band (i.e. between 3 MHz and 30 MHz), this property is turned to good account, by radar and communication systems, in order to cover very large areas. Two propagation modes have to be distinguished: the surface wave mode and the sky wave mode. In the first one, the wave is guided by the air/ground interface. As a consequence, the surface waves follow the earth curvature and reach non-LoS regions. Sky waves, as for them, are refracted by the ionosphere at very large distance (Figure 1).