Novel reduced-size lumped-element coplanar waveguide (CPW)-to-coplanar stripline (CPS) transitions are proposed, using planar parallel and series inductor-capacitor (LC) circuits to realize the effective open circuit and short circuit, respectively. In this study, various compact lumped-element Marchand-balun type CPW-to-CPS transition structures are developed and carefully examined. The design of proposed transitions can easily be accomplished by the use of conventional filter synthesis techniques. Simple equivalent-circuit models are also established, from which the passband behavior of the lumped-element transition structures may be characterized.