Numerical analysis of tunable periodic structure is developed in this thesis through the use of the simulative software CST Studio Suite on the single unit cell. To this end, four different configurations were designed and analyzed. The starting unit cell consists of three different resonators namely an inner, a central, and an outer ring. The resonators, with diverse resonant frequencies, are connected by microstrip lines. The other three configurations are differentiated by the presence, location and number of cuts that were inserted in the connecting lines. All configurations are implemented on FR-4 substrate. On the opposite face of it three microstrip lines are considered, having the role of biasing active elements inserted in the cuts.