A full-wave spectral-domain technique is developed to investigate the characteristics of periodically nonuniform coplanar waveguides (CPW). The Floquet theorem is employed to express all the field quantities in terms of the spatial harmonics, so that the boundary-value problem of a periodically nonuniform coplanar waveguide can be treated similarly to that of the uniform one. The Galerkin method in the Fourier spectral domain with a set of appropriate basis functions is used to obtain numerical results for characteristics of the sinusoidal-shaped coplanar waveguides. The filterlike propagation property of the periodic structure is exploited in the realization of a band-stop filter. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 59–66, 1997.