New bandstop filter based on capacitively coupled λ/4 short-circuited lines embedded into U.S. UWB BPF

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