Analysis of periodic shielded microstrip lines excited by nonperiodic sources through the Array Scanning Method

In this paper we aim at rigorously studying the practical excitation of a shielded microstrip line periodically perturbed by gaps. In particular a delta-gap voltage source is considered in an environment shielded by lateral and top metallic walls. The excitation problem is solved through a numerical implementation of the array scanning method, in which the field excited by a nonperiodic source in a periodic environment is represented as an integral superposition of fields, which are solutions of suitable auxiliary Floquetperiodic problems. To solve the latter, a spectral-domain method-of-moments approach has been adopted, introducing original acceleration techniques to enhance the efficiency and accuracy of the method. The numerical performance of the spectral-domain approach is illustrated and fully validated. Results are presented both for the dispersive properties of Bloch modes supported by the structure in the absence of excitation and for the currents excited on the structure by a single delta-gap source, also discussing the modal representation of such currents in terms of Green’s function singularities in the spectral plane of the longitudinal wavenumber.