Design of balanced UWB BPF based on quint-mode slotline resonator

In this paper, a quint-mode slotline resonator (QMSR) is analyzed and designed. The proposed resonator has similar performances to those of the conventional microstrip multimode resonator, while it is located at the bottom ground layer. To the best of our knowledge, this is the first time that QMSR is proposed. By properly adjusting the dimensions of the proposed QMSR, quasi-independent control of the five resonant frequencies is realized, thereby an ultrawideband (UWB) differential-mode (DM) transmission passband can be obtained. By employing balanced microstrip/slotline transition structure, a high and wideband common-mode (CM) suppression can also be realized, which is independent of the DM responses. Thereby, only the DM performances need to be considered, which simplify the design procedure greatly. In addition, one notched band is achieved to suppress the special electromagnetic interference. To validate the design concept, one prototype circuit of the proposed balanced UWB bandpass filter is implemented following the given design procedure. Good agreement between the measurement and simulation results can be observed.