Full-wave analysis of periodic microstrip lines excited by an aperiodic delta-gap source

A study is presented of the current excited on a printed periodic structure by a single aperiodic source. In particular, both completely shielded and open microstrip lines periodically loaded with gaps are considered, excited by a delta-gap voltage source. The aperiodicity of the source does not allow for a direct application of the Floquet theorem. The Array Scanning Method (ASM) is then applied, which reduces the aperiodic problem to an integral superposition of suitable Floquet-periodic problems. Efficient numerical implementations of the ASM are developed, for both the shielded and the open cases, based on the method of moments with entire-domain basis functions. Numerical results are presented for dispersion features and Bloch modes supported by the periodic microstrip line and for the current excited by the source in different frequency ranges corresponding to passband and stopband regimes of the fundamental perturbed quasi-TEM mode.