Dual Band Bandpass Filter Using Multilayer Structure

In this paper, a new method to design a dual band bandpass filter (BPF) is presented. This method is based on a simple principle: different substrates (dielectric constants) will result different resonant frequencies for a resonator. The basic structure of this method is studied and then a planar band pass resonator is designed to utilize in this structure. Response of the proposed dual layer filter is tuned using resonator shifting and resonator scaling. In addition to improve the filter response, resonator shifting improves the filter size. The final structure is designed, fabricated and measured and simulation results are in good agreement with measured values. The central frequencies of this dual band BPF are f1=3.85 GHz and f2=5.3 GHz and a deep transition zero at 4.57 GHz, guarantees isolation between passbands.