In this paper, coplanar waveguides (CPWs) periodically loaded with shunt-connected capacitances and periodically perturbed by varying the slot width are studied. Both square- and sinusoidal-shaped structures are considered. It is demonstrated that by a proper choice of the perturbation period, the spurious passbands-inherent with the presence of reactive elements-can be completely rejected, even in the case of singly tuned (sinusoidal) structures. Rejection levels near and above 30 dB (depending on the spurious band), inferred from electromagnetic based simulations, are experimentally verified. © 2003 Wiley Periodicals, Inc.