Compact Size of an Interdigital Band-Pass Filter with Flexible Bandwidth and Low Insertion-Loss Using a Folded Spiral and Stepped Impedance Resonant Structure

A conventional interdigital bandpass filter (BPF) is characterized by coupled and tapped lines affords low insertion loss (IL) easy fractional bandwidth (FBW) adjustment. However, the maximum FBW of limited to 30%, beyond that, its gap size increases, thereby rendering fabrication impractical on a standard printed circuit board. In addition, cannot be changed because it dictates operational frequency filter. Hence, in this study, we propose compact BPF based spiral folded stepped impedance resonator (SIR), which IL excellent group delay. The spiral, structure facilitates drastic adjustment: center adjustable range designed are 800 MHz 80 180%, respectively. Additionally, proposed can adjust k-factor from 180%. return losses 0.043 dB 17.1 dB, respectively, delay 0.098 ns. total only 13.8 mm × 5.98 mm, corresponds reduction factors >2/8 relative 2.1 latest design. difference between other filters 0.15 for 1.36 times different than filters.