Compact dual-band microstrip bandpass filter using stub-loaded stepped-impedance resonator

In this paper, two dual-band microstrip bandpass filters (BPFs) based on the stepped-impedance resonator (SIR) and stub-loaded SIR (SL-SIR) are presented. The characteristics of the SL-SIR are studied by using the even-/odd-mode analysis method. The simulation results show the length of the loaded stub has no influence on the odd-mode resonant frequency, but it can affect the even-mode resonant frequency. In addition, the BPF based on the SL-SIR has higher frequency selectivity and stopband rejection than the one based on the SIR. What's more, the loaded stub can reduce the size of the BPF. Therefore, the BPF based on the SL-SIR can be applied in the modern wireless communication systems.