Relation between surface impedance and bandwidth of hard surface

Shows that the bandwidth of a hard surface is always inversely proportional to the diameter of the guiding structure. This seems to be a general relation that is independent of the way the hard surface has been realised. The corresponding relation for an open hard surface seems to be that the bandwidth is inversely proportional to the length of it. These two relations limit applications of the hard surfaces to structures that have small such critical dimensions. Such applications of hard surfaces with small critical dimensions have been experimentally verified and show reasonable bandwidths (10-2046). The present study has also shown that the bandwidth can be improved if materials with high wave impedances are used to realise the hard surface. Finally, it is mentioned that the hard strut can represent a useable model in order to experimentally test different realisations of hard surfaces. Theoretical searches for such surfaces can be done with computer codes that can model plane wave reflection from arbitrary single or double periodic surfaces. The paper considers the frequency characteristics of the hard surfaces when the surface is applied for horn antennas and waveguides.