Design of Dual-Band Bandpass Filter with Wide Upper Stopband Using Sir and Gsir Structures

In this paper, a new dual-band bandpass (BPF) filter with multi-spurious suppression is proposed, which is composed of step-impedance resonators (SIR) and grounded-step-impedance resonators (GSIR). It is shown that the resonant frequencies of GSIR can be obtained similar to SIR. Then, by determining the dimensions of SIR to have a specified resonant frequencies ratio, the dimensions of GSIR can be calculated. It is also shown that the coupling lengths between SIR and GSIR can create several transmissions zeros and can be used to suppress the unwanted higher order resonant frequencies. A third-order filter is designed and fabricated to operate at two WLAN frequencies of 2.45 GHz and 5.8 GHz. The measured results show a rejection level of 24 dB up to more than 17 GHz (7). Simulation and measurement results are in good agreement with each other.