Balanced Dual-Band Bandpass Filter Based on Asymmetrical Coupled Lines

In this article, a balanced dual-band bandpass filter is proposed based on the asymmetrical coupled lines formed by stepped-impedance resonators. The high-impedance lines of stepped-impedance resonators are coupled with the low-impedance lines of stepped-impedance resonators respectively, and two segments of asymmetrical coupled lines have different coupled gaps. The differential-mode resonant frequencies of the proposed filter are decided by stepped-impedance resonators, and better common-mode signal suppression is obtained by adjusting the two coupled gaps. The measured results show that the center frequencies of the filter are 2.43 GHz and 5.23 GHz with insertion losses of 1.5 dB and 1.9 dB, respectively. Moreover, the common-mode signals are suppressed to -31 dB and -46.5 dB at 2.43 GHz and 5.23 GHz.