Coplanar Waveguides for MMIC Applications: Effect of Upper Shielding, Conductor Backing, Finite-Extent Ground Planes, and Line-to-Line Coupling

Parasitic effects occurring in actual realizations of coplanar waveguides (CPW) for microwave integrated circuits on GaAs substrates, such as the influence of an upper shield, conductor backing, finite-extent ground planes, and line-to-line coupling, are discussed and evaluated. CAD-oriented analytical expressions are obtained for the electrical quasi-TEM parameters of the relevant waveguiding structures by means of exact or approximate conformal mapping techniques. Differences in electrical behavior with respect to ideal CPW´s are highlighted, and practical design criteria are obtained for keeping cover height, ground-plane width, and line-to-line spacing effects to a minimum.