The Nature of the Radiation at Low Frequencies from a Class of Periodic Structures

In this work novel behavioural features are found for the propagation and the radiation of a class of periodic structures commonly employed in various microwave passive devices and antennas. Referring in particular to an open waveguide consisting of a dielectric layer periodically modulated by a strip grating, it is shown that the low-frequency properties of the fundamental space harmonic vary as a function of the ratio of the strip width to the overall period, giving rise to unusual and initially-puzzling dispersion behaviours. We have also discovered a new complex modal solution, whose behaviour explains well both the radiative and the reactive effects in this class of structures.