The high frequency characteristics of hybrid structures made from indium tin oxide (ITO) films and very fine gold (Au) lines were theoretically and experimentally investigated to develop invisible coplanar waveguide (CPW) structures for microwave and millimeter-wave applications. After optimizing the Au/ITO hybrid structures, we achieved fabrication of an invisible CPW structure showing both high transmission and low reflection characteristics in the GHz range. Electromagnetic simulations by using a finite elements method explained the reason for the improved characteristics of the optimized Au/ITO hybrid CPW. (C) 2011 Elsevier B.V. All rights reserved.