High-Selectivity Wideband Balanced Bandpass Filter with Multiple Transmission Zeros and Poles

Abstract

A novel high-selectivity wideband balanced bandpass filter (BPF) with multiple transmission zeros and poles is proposed for WiFi applications. The half-wavelength microstrip transmission lines enable differential transmission of signals. By using shorted coupled lines and folded 270° transversal transmission lines, the proposed balanced BPF can achieve multiple transmission poles and multiple transmission zeros as well as wideband high selectivity performance for differential-mode signals. One-quarter wavelength open-circuited stubs loaded on the symmetry plane are utilized in series with absorption resistors to realize common-mode (CM) noise suppression. The proposed balanced BPF has four transmission poles in-band and five transmission zeros out-of-band. The 3-dB fractional bandwidth is 89.4% from 1.33 GHz to 3.41 GHz. The CM noise suppression is better than 16.7 dB in the passband.