TIME-HARMONIC AND TRANSIENT SCATTERING BY FINITE PERIODIC FLAT STRIP ARRAYS - HYBRID (RAY)-(FLOQUET MODE)-(MOM) ALGORITHM

Finite periodic structures are of interest in a variety of narrow-band applications. With the trend toward wider bandwidth, culiminating in the ultra-wideband or short pulse (SP) regime, it is of interest to explore how well defined narrow-band wave fields, such as the dispersive periodic structure modes, behave under SP conditions. These considerations have motivated the present frequency and SP time-domain (TD) study of two-dimensional plane wave scattering from a finite periodic array of thin, flat, coplanar perfectly conducting strips. Rigorous analytical-numerical reference solutions are established by spatial spectral wave number decomposition and the method of moments (MOM), followed by frequency inversion. The analytical portion is approximated so as to yield via high-frequency asymptotics, for a sufficiently large number of strips, a hybrid ray-(Floquet mode)-MOM algorithm which not only explains the phenomena in physical terms but is also numerically efficient and reasonably accurate when compared with the reference solution. Of special interest are the TD Floquet modes with their space-time dependent frequencies and wave numbers. By superposition, they can synthesize the highly resolved pulse train return under SP conditions. Attention is given also to direct SP-TD synthesis, and to processing options of SP-TD data.