Novel concept for microstrip stub resonant frequency control

Abstract

A novel concept for controlling a low-cost tunable microstrip filter is proposed. The microstrip stub controlling 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 1 GHz. An equivalent circuit model of the resonator is developed. Calculation results are in good agreement with finite-difference time-domain method (FDTD) and finite elements method (FEM) simulations.