IMPROVED COMPACT BROADBAND BANDPASS FILTER USING BRANCH STUBS CO-VIA STRUCTURE WITH WIDE STOPBAND CHARACTERISTIC

Abstract—In this paper, a broadband bandpass filter (BPF) with superior spurious suppression over a wide frequency range at least up to 20 GHz at −20 dB has been designed. The proposed broadband bandpass filter has designed using quarter-wavelength short stubs alternating with branch stubs co-via structure, and inserting the bandstop filters to substitute for redundant connecting lines. Compare with some traditional co-via structure, this work by using the branch stubs to construct the co-via structure, not only reduce the size around 70 % but also decrease the radiation loss due to some complex meander 46 Lin et al. configurations occurring in the connecting lines. For the prototype broadband filter, center frequencies around 4 GHz were selected. The bandwidth of passband was between 1.95 GHz and 6.25 GHz, in which the insertion-loss amounts to around−1.5 dB. The suppression range of stopband is between 8.2–20.3GHz, in which the insertion-loss amounts to around −20 dB. 1