An ultra-wideband bandpass filter using a new defected ground structure resonator and interfinger-capacitor microstrip is proposed,which is constructed by a cascading microstrip high-pass filter and a low-pass filter.The low-pass filter with a 3 dB cutoff frequency of 6 GHz is composed of a widened microstrip line on the top plane and a combined open-loop defect ground structure on the ground plane,achieving high selectivity and good stopband performance.The high-pass filter consists of a microstrip interfinger capacitor in the top plane and an open-loop defect ground structure in the ground plane,resulting in two transmission zeros and steep selectivity.The designed ultra-wideband bandpass filter has a 3 dB bandwidth of 2.5 GHz and a center frequency of 4.8 GHz,showing a sharp cut-off frequency response.It also exhibits good stopband performance,with lower stopband from DC to 3.45 GHz and upper stopband from 6.4 to 12 GHz,suppressing better than 20 dB.
bandpass filterdefected ground structureresonatorstopbandbandwidthcut-off frequency
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