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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) in order to omit 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.Corresponding author: N. Molaei Garmjani (nima molaei@yahoo.com).

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In this article, a triplexer is presented for three operation frequencies in GSM, based on stepped impedance resonators (SIR). SIR structures have some characteristics, such as low weight, little dimension, and the ability of providing filter behavior with different frequencies in same dimensions. To design the triplexer, bandpass filters of each output should be design first. Parallel connection of three filters together causes an extreme increase in insertion loss of each filter and also reflection of power to the input. A novel based-on-SIR matching circuit is proposed to solve these problems. By connecting optimized matching circuits to three bandpass filters [1], which are simulated for three frequency ranges in GSM, the desired triplexer is obtained. This based-on-SIR triplexer is simulated and fabricated. The measurement results of the fabricated prototype shows a good agreement with simulation results.