In this paper, design and fabrication of a quad-band microstrip bandpass filter (BPF) using multi-layered stepped impedance resonators (SIRs) structure is proposed. One pair of SIR on the top layer is designed to operate at the 1st and 3rd passbands (1.56/3.57 GHz), and the other pair is at 2nd and 4th passbands (2.42/5.23 GHz) by tuning the impedance and length ratios of the SIRs. In order to find the desired coupling location between the SIRs located on different layers and the input/output (I/O) lines, the voltage, current and power wave on the I/O lines are analyzed. It is verified that the proposed quad-band filter has good passband performances with an excellent isolation between adjacent bands for GPS, WLAN, and WiMAX applications.
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