A compact bandpass filter using folded λ/4 coupled-line resonators

This paper presents a compact bandpass filter using folded λ/4 coupled-line resonators. Accurate model of this resonator and equations for extraction of the equivalent parallel-coupled-line structure representing the folded-line section are developed. A simple systematic design procedure is established for filter designers. Finally, a 3-pole bandpass filter with the new resonators is designed. The new folded-coupled-line filter exhibits a significant reduction in footprint compared to the conventional design.