Quasi-elliptic SIR bandpass filter with Defected Ground Structure

In this paper, a quasi-elliptic bandpass filter was designed, simulated, and fabricated using four-pole cross-coupled stepped impedance resonators (SIR). Using a special type of stepped impedance resonators, a great increase in rejection band width of the filter was obtained. In order to perform the mentioned design practically, we utilized a compound sandwich model of two substrates (in strip line form). Furthermore, we used Defected Ground Structure (DGS) on both of upper and lower ground planes, in order to eliminate the first spurious resonant frequency and increase bandwidth of the filter. The fabricated sample was measured and the results showed a good agreement with simulated results.