'Add-on' analysis of large irregular strip arrays

The add-on procedure begins with an initial expansion of the unknown current distribution into subdomain (pulse-type) basis functions, similarly to the moment method (MM). However, rather than generating a matrix equation as in the MM, the author computes the amplitudes of the basis functions (denoted as pulse responses) in a gradual manner whereby the scatterer is being built up from the segments as they are being added one at a time. At the end of each addition, the result for a physical subproblem is obtained. At each stage, a scattering problem need be solved for the additional segment only, implying a 1 × 1 matrix inversion that yields the amplitude of the added segment in the presence of the other segments existing at that stage. The amplitudes of these segments are updated to account for the presence of the additional segment. This process is repeated for each segment. The problem of large finite irregular arrays of strips, of 100 to 600 wavelengths wide, was treated using the add-on method. These problems require handling of 1000 to 6000 unknowns. An example for a 1000-unknown case is shown for the E-polarized case. Computation time for this problem, including all the subproblems, was 20 minutes on a VAX 11/785.