Some experiences from FDTD analysis of infinite and finite multi-octave phased arrays

Some experiences from finite-differences time-domain (FDTD) analysis of infinite and finite multi-octave phased arrays are presented. First, a more unified derivation of equations suitable for unit-cell analysis of phased arrays or other types of periodic structures using FDTD is presented. Second, results from FDTD calculations of small to very large multi-octave finite arrays are summarized in order to answer the question of how large an array model must be in order to capture the characteristics of both the interior and the edge elements of a large multi-octave phased array. It is found that a considerably larger number of elements is required in the broad-band case than in the normal narrow-band case, and it is also found that FDTD is well suited for such calculations. Third, simple methods to save computer memory using locally fine grids in an otherwise coarse FDTD grid to model finite-phased arrays are explored. The two local grid methods tested were found in our application to suffer from numerical instabilities.