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

In this letter, a novel high selectivity and common-mode (CM) suppression wideband balanced microstrip passband filter (BPF) is proposed using the short stub centrally loaded short-ended resonators (SSCLSR). The odd-mode resonant frequency of the SSCLSR can be flexibly controlled by the short stub, whereas the even-mode one is fixed. First, the wideband single-ended BPF are designed based on the microstrip SSCLSR with the parallel coupled microstrip line input/output (I/O). Two transmission zeros near the passband edges can be generated due to the main path signal counteraction and source-loaded coupling. Further, the CM equivalent half circuits of the balanced BPF based on the wideband single-ended BPF are investigated in detail. Thus, a wideband balanced BPF with high CM suppression within the passband is designed, fabricated, and measured. Good agreement between simulated and measured results is obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2940–2944, 2014