Compact Balanced Bandpass Filter With Wideband Common Mode Suppression

A compact balanced bandpass filter with wideband common mode suppression is proposed. Swap structures based on double-sided parallel-strip line (DSPSL) are used to realize 180° phase invert, which can provide an inherent common mode suppression in a wideband, and compared with half-wavelength transmission line in other work, this swap structure greatly reduces the size of the balanced filter and achieve a compact structure. Two transmission zeros are introduced by dual-mode ring resonator lead to high selectivity. One prototype center at 2.2 GHz was designed and fabricated, 3-dB factional bandwidth of 23.6% and over 20 dB common mode suppression extend to $2.91f_{0}$. Simulated results are in good agreement with measured results.