An equivalent-circuit model for a reconfigurable unit cell is proposed. This circuit model facilitates fast prediction of scattering parameters and dispersion analyses of a reconfigurable periodic structure. The cutoff frequencies obtained using equivalent-circuit models are in excellent agreement with those from measurements and full-wave numerical simulations. The proposed circuit model is then modified to include non-ideal, commercial RF FET switches. The effect of such a switch in each state, On or Off, is modeled by a frequency-dependant impedance, derived from the scattering parameters of the switch. The proposed technique can be used to analyze a reconfigurable periodic structure with any type of switches. For the structure with 24 unit cells considered here, the equivalent circuit model is about five orders of magnitude faster than full-wave simulations.