2015 Volume E98.A Issue 10 Pages 2171-2177
A novel high common-mode (CM) suppression wideband balanced passband filter (BPF) is proposed using the stub centrally loaded slotline resonators (SCLSR) which have two resonant frequencies (odd- and even-modes) in the desired passband. The odd-mode resonant frequency of the slotline SCLSR can be flexibly controlled by the stub, whereas the even-mode one is fixed. Meanwhile, a transmission zero near the odd-mode resonant frequency can be generated due to the main path signal counteraction. First, the wideband single-ended BPF and corresponding balanced BPF are designed based on the slotline SCLSR with the parallel coupled microstrip line input/output (I/O). Ultra wideband high CM suppression that can be achieved for the slotline resonator structure has no resonant mode under CM excitation. Furthermore, by folding the parallel coupled microstrip line I/O, the source-load coupling is effectively decoupled to improve the CM suppression within the passband. The high suppression wideband balanced BPF is fabricated and measured, respectively. Good agreement between simulation and measurement results is obtained.