In this article, a new tri-band bandpass filter, operating at 2-2.6 GHz, 3.5-4.5 GHz and 5-5.8 GHz for GSM, WiMAX and WLAN application is proposed. Two quad sections SIR resonators and corresponding feeding structures are introduced to enhance the tuneable range of operating frequencies. Using source/load coupling can realize two controllable transmission zeros around each operating band. The filter is analyzed and solved in terms of the transmission line model using finite element method (FEM) and results are refined by full-wave simulator CST Microwave Studio 2009 and SONNET Version.11. The comparison between magnitudes of s-parameters simulation results with SONNET and CST Microwave Studio simulators are also presented. The results show a good match between two simulation results with different commercial software for the proposed bandpass filter. The desired operating bands are covered by the response of the different software’s.