Miniaturized Wideband Pole-Zero Following Tunable Bandstop Filter for 5G Millimeter-Wave Application

A miniaturized wideband CMOS pole-zero following tunable bandstop filter (BSF) structure is proposed for 5G millimeter-wave application. The proposed simple tunable BSF configuration provides two transmission zeros and one transmission pole, which exhibits a compact size, wide stopband and sharp rejection. Benefiting from the pole-zero following feature, the tunable BSF maintains consistent selectivity as the frequency changes. Theoretical analysis is explored to provide physical insight into the working mechanism of the BSF. For practical validation, two prototype tunable BSFs (transformer-type and LC-type) operating at 28 GHz are fabricated using 65-nm CMOS technology. The measured results are in good agreement with electromagnetic (EM) simulations.