Analytical and numerical techniques in the Green´s function treatment of microstrip antennas and scatterers

In the paper, the mode theory of wave propagation in stratified media is used to establish the spatial Green´s functions associated with a microstrip structure. They correspond to the fields and potentials created by a horizontal electric dipole placed on the air/dielectric interface and are expressed as Sommerfeld integrals. Near- and far-field approximate analytical evaluations of these integrals are rigorously derived. They allow a quantitative discussion of the scope and limitations of the static microstrip theory, and point out the relevance of surface wave effects in microstrip. The most interesting situation when both source and observer are in the air/dielectric interface is studied extensively. Numerical methods to evaluate Sommerfeld integrals in such situations are reviewed, and several new accurate techniques are introduced and discussed in detail.