Waves on interfaces

In wave propagation along plane or cylindrical interfaces a distinction is made between truly guided waves (surface waves) and partially guided waves (radiating waves). When dissipation losses are involved, surface waves no longer represent the asymptotic field near the interfaces at large distances from the source. In order to separate them from the total field it is necessary to have a criterion for radiating waves which are free of any surface wave components. Such a criterion exists in the form of orthogonality relations which are the mathematical formulation of the concept that an ideal antenna which excites only a surface wave should not receive a radiating wave.