Design of Bandpass Filters Using Miniaturized Stepped-impedance Resonators

A fourth-order higher selectivity band-pass filter using miniaturized open-loop Stepped-Impedance Resonator (SIR) is designed and fabricated. The central frequency of the filter is 2.45GHz and the bandwidth is 8%. By using miniaturized open-loop SIR resonator, we design filter based on cross-coupling, input and output external quality factor. A single transmission zero is realized by the cross coupling in the structures, which can improve the skirt selectivity of the filter. The circuit size of a miniaturized open-loop SIR band-pass filter reduces to 50% of the square open-loop resonator band-pass filter. The results of measurements are in good agreement with the full-wave simulation results.