Tri-band bandpass filter based on coupled stepped impedance resonators

A novel tri-band bandpass filter (BPF) is proposed by using cross-coupled stepped impedance resonators (SIRs), which can operate at 2.4 GHz, 3.5 GHz and 5.25 GHz respectively. In engineering application, it is suitable for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX). In addition, the passband of this filter can be easily controlled by changing the electrical parameters of the resonators. So it is helpful to the selection of passband in engineering applications. For in-depth analysis, the equivalent circuit of the filter is also proposed. At last, it shows that the measured results agree well with the simulated results. The insertion loss of the filter within each passband is less than 1.9 dB, meanwhile two transmission zeros are obtained which can be able to meet the engineering requirements.