A common mode filter using DGS-based coupled multiple resonance points for all-pass differential circuit

An ultra wideband common-mode filter based on coupling multiple resonance points is proposed in the letter. The resonant are realized by four compact defected ground structure (DGS) cells, of which both ends C-type DGS cells and middle H-type cells. size these units different, leads to their different points. Because close distance between inductors generated them, can be used for smoothing filtering. A coupled LC resonator equivalent circuit model built explain filter’s working principle. DGS-based with an area 20mm × 12mm implemented under differential microstrip line. simulated results shows achieves a wide 15-dB suppression frequency range from 2.9 12.6GHz. Good agreement full-wave simulation measured observed.