A novel bandpass filter with dual-mode open-loop resonators

In this paper, we propose a novel microstrip bandpass filter (BPF) based on dual-mode open-loop resonators (DMOLRs). The proposed bandpass filter consists of two coupled DMOLRs, which can be treated as the combination of a folded T-shape stub and a W-shape stub. An equivalent circuit model of the microstrip bandpass filter is employed to estimate the electromagnetic transmission characteristic for practical realization. The microstrip bandpass filter is fabricated and tested. The tested results show that a 3dB bandwidth 400MHz, insertion loss of -0.42dB, and minimum return loss of -20.9dB at center frequency of 2.4GHz. The total size of the proposed device is 0.5λg×0.21λg. Good agreement between the simulated and measured results demonstrates the validity of the proposed BPF. Good agreement is obtained between the simulated and the measured bandpass filter characteristics.