Tunable band-stop and band-pass filters based on microstrip stub resonators

A novel concept for controlling of tunable microstrip resonators is proposed. The microstrip stub control is realized by detaching a part of the stub from the substrate. The air gap between the substrate and the signal electrode is the heterogeneity which controls the stub effective permittivity, in this way providing a resonance frequency shift. By moving the stub 50 microns the resonance frequency is shifted about 0.7 GHz (30%). An equivalent circuit model of the resonator is developed. Measurements results are in good agreement with circuit model, finite-difference time domain method (FDTD) and finite elements method (FEM) results.