The problem of aperiodic excitation of periodic structures with periods larger than a half-wavelength is revisited. A large number of antennas and other electromagnetic wave propagation problems fall within this category. Because of the overlapped branch cuts, the conventional path deformation techniques employed in application of the array scanning method for this type of problem fail when the period is larger than a half-wavelength. A new method based on the subdivision of the integration path and using the double exponential quadrature formula is introduced to alleviate this problem and apply the array scanning method to structures with an arbitrary spatial period. To demonstrate the application of the new method and to validate the results, three important electromagnetic problems are solved using new proposed method : 1) Calculation of reflection and transmission coefficients and near fields of a frequency selective surface excited by a single electric dipole 2) Full-wave analysis of a low profile printed dipole antenna on EBG ground plane 3) Calculation of radiation pattern and input impedance of a resonant dipole embedded in 2D periodic leaky-wave structure. In all problems the Green’s function of aperiodic source in the presence of a 2D periodic structure is obtained by means of array scanning method. Numerical obtained results have excellent agreement with results of commercial softwares (FEKO and HFSS) while the proposed method shows considerable advantage in terms of computational time and memory requirement. Key Words Electromagnetic periodic structures, aperiodic source, array scanning method, 2D leaky-wave antenna, low-profile antenna.
