High Performance Balanced Bandpass Filters With Wideband Common Mode Suppression

• Published in: IEEE transactions on circuits and systems. II, Express briefs Express briefs, 2021-06, Vol.68 (6), p.1897-1901
• Main Authors: Feng, Wenjie, Pan, Bosang, Zhu, Haoshen, Zhou, Xin Yu, Che, Wenquan, Xue, Quan
• Format: Article
• Language: English
• Subjects: Balanced bandpass filter; Band-pass filters; Bandpass filters; Broadband; Circuits; common mode (CM) rejection; compact; double-sided parallel-strip line (DSPSL); Equivalent circuits; Filtering theory; high selectivity; Impedance; Microstrip transmission lines; Optical ring resonators; Passband; Rejection; Resonator filters; Resonators; Selectivity
• ISSN: 1549-7747; 1558-3791
• DOI: 10.1109/TCSII.2020.3044092

Two compact and high selectivity balanced bandpass filters with excellent common mode rejection are designed in this brief. Compared with the half-wavelength microstrip transmission line, 180° phase shift is realized by two small swap structures, which are composed by double-sided parallel-strip line (DSPSL), and this way can easily realize a wideband common mode rejection with compact circuit size. Two out-of-band transmission zeros are introduced by the dual-mode ring resonator in the first proposed structure; thus, high selectivity can be achieved. In the second filter, shorted/open coupled microstrip lines are added between the dual-mode ring resonator and 180° swap structure, two additional transmission zeros can be achieved. Finally, two prototypes center at 2.2 GHz are fabricated, and the measured 3-dB bandwidths for the differential mode are 23.6% and 11.8%, respectively.