Strip-Loaded Slotline Resonator for Compact Differential-Mode Bandpass Filters with Improved Upper Stopband Performance

In this letter, a strip-loaded slotline resonator (SLSR) is presented and applied to design a class of novel differential mode (DM) bandpass filter (BPF) with improved upper stopband, compact size and intrinsic common-mode (CM) suppression. This DM BPF is composed of three paralleled coupled SLSRs, and two differential tapping-coupled ports. As the loaded-strip length is stretched, the 1stresonant frequency gradually falls down so as to make the SLSR compact in size, while the 2ndone is tremendously raised towards the 3rdone so as to widen the spacing between the 1stand 2ndresonant frequencies or achieve a wide upper stopband of the proposed DM BPF. To verify the proposed technique, a third-order DM BPF prototype has been designed and fabricated. Both the simulated and measured results have demonstrated good DM upper stopband and CM rejection in addition to compact size.