Lowpass filter with sharp roll-off and wide stopband using LTCC technology

A compact lowpass filter (LPF) with both sharp roll-off and wide stopband is presented in this paper. The proposed LPF is realized by cascading modified hairpin unit consisting of one U-shape stripline and one pair of offset-coupled striplines with multilayer low-temperature co-fired ceramic (LTCC) technology. By controlling the relatively positions vertically and horizontally of the offset-coupled striplines, we can get the tunable even-mode and odd-mode impedances of coupled lines in wide range. Measured results indicate that the designed filter has an ultra-wide stopband rejection better than 10 dB up to 20 GHz and a sharp roll-off of 81 dB/GHz. Furthermore, the size of the filter is only 4.54 × 3.37 mm2.