Wideband Bandstop Filter Based on Capacitively Coupled λ/4 Short-Circuited Lines

Abstract

A new wideband bandstop filter(BSF) with a sharp roll-off characteristic is introduced in a stripline structure in this paper. The BSF consists of two sections: the first is two capacitively coupled λ/4 short-circuited lines with opposite ground positions, while the second is a capacitively coupled λ/4 short-circuited line. The BSF provides three transmission zeros within the stopband and better than 22 ㏈ rejection over the whole wireless local area network (WLAN) band from 5.15 to 5.825 ㎓. The BSF, cascaded to an U.S. ultra-wideband(UWB: 3.1~10.6 ㎓) bandpass filter(BPF), is simulated with HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape with a dielectric constant of 7.8. The measurement results agree well with the HFSS simulation results. The size of the UWB BPF including the BSF is 3×6.3×0.45 ㎣.