Longitudinal coupling between elements in a disc-on-rod antenna array

A general analytical expression for the coupling of surface wave antennas is derived, on the basis of the equivalence principle and the reciprocity theorem. The expression can be used to determine the extent of longitudinal coupling for two disk-on-rod antennas at various distances from each other. It is found through a series of calculations that coupling occurs in relation to the increase in frequency when the antennas are close together, while for larger distances coupling is related to decreases in frequency.