Surface waves are a key point for High Frequency radars. Our global objective is to improve or avoid their excitation depending on whether we operate surface wave radars or sky wave radars. This paper deals with suppression of surface wave for high frequency sky wave radar. We aim to develop periodic sub-wavelength structures like metamatrial ones. Indeed, considering HF wavelength, we have the opportunity to build objects with reasonable size and relatively poor accuracy constraints. We present first results of our studies.