COMPARISON OF QUASI-STATIC AND EXACT ELECTROMAGNETIC FIELDS FROM A HORIZONTAL ELECTRIC DIPOLE ABOVE A LOSSY DIELECTRIC BACKED BY AN IMPERFECT GROUND PLANE.

In most microstrip transmission lines, analysis is made assuming that a quasi-TEM mode exists and propagates down the line. The authors seek to obtain the region of validity of this assumption. Their second objective is to derive the expressions for the fields for a horizontal electric dipole over a lossy dielectric medium backed by an imperfect ground plane. It is shown that, to a first approximation, fields at the air-dielectric interface are independent of the ground plane conductivity. Since attention is confined to coupling between lines, the goal is to computate the fields primarily at the air-dielectric interface. Finally, numerical results are presented to show where the quasi-static approximations deviate from the exact solution for a given microstrip geometry as the frequency of operation or the observation point is changed.