High CM suppression balanced BPF with two CM transmission zeros

Abstract

A new compact, low insertion loss, and wide stopband balanced bandpass filter (BPF) with two common‐mode (CM) transmission zeros within the differential‐mode (DM) passband is designed in this article. The DM filtering topology is formed by two quarter‐wavelength resonators and a short stub loaded source‐load coupling structure which can generate new transmission zeros to improve the selectivity and suppress the harmonic to widen the stopband. The center‐loaded step‐impedance open stub can be applied to misalign two CM fundamental resonant frequencies, meanwhile adjust one CM transmission zero to the DM passband. To enhance the CM suppression within the DM passband, another CM transmission zero is created by the folded stub loaded in the 50‐Ω input feedline which creates the first DM transmission zero located at 2 f0d ( f0d is the center frequency of DM passband) and has little effect on the DM in‐band and lower‐stopband performance. Finally, a high CM suppression balanced BPF prototype for WLAN application is designed and fabricated. The simulated and measured results show a good agreement. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:135–141, 2014

Novel quasi‐reflectionless balanced bandpass filters using absorption network for common‐mode and harmonic suppression

“…4,5 Moreover, distributed or lumped elements are loaded along the symmetrical plane of the BPFs to improve the CM suppression in the differential-mode (DM) passband. [6][7][8] Good balanced performance is achieved in these works. However, the out of band DM signal and CM noise are reflected back to the source in these traditional balanced BPFs, which may have great influence on nonlinear devices.…”

“…Many methods for CM rejection in balanced BPFs have been reported, such as coupled‐line structures with multitransmission zeros (TZs), 1 swap structures with intrinsic CM suppression based on double‐sided parallel‐strip line, 2,3 and slot line structures 4,5 . Moreover, distributed or lumped elements are loaded along the symmetrical plane of the BPFs to improve the CM suppression in the differential‐mode (DM) passband 6–8 . Good balanced performance is achieved in these works.…”

An unbalanced-to-balanced diplexer based on substrate integrated waveguide cavity

“…So far, most of the work about balanced circuits are focused on balanced filters , baluns , or balun filters . Only relatively little research has been done on the unbalanced‐to‐balanced diplexer.…”

High CM suppression wideband balanced microstrip BPF using dual‐mode resonator

“…To further improve the CM suppression level, the balanced BPFs in were designed by loading the proper open stub, capacitor, or resistor in series at the center of the half‐wavelength resonator or SIR, which can obtain high CM suppression while keeping the DM response almost unchanged. In our previous work , the CM suppression within the passband can be greatly improved by introducing one or multiple controllable CM transmission zeros within the passband.…”