In　this　paper,　an　ultra-wideband　(3.1∼10.6GHz)　active　variable　attenuator　is　designed.　Π-attenuator　circuit　topology　and　SiGe　HBTs　active　devices　are　employed　to　achieve　high　gain　dynamic　range.　LC　series　negative　feedback　at　emitter　is　used　to　achieve　flat　gain,　and　RC　shunt　negative　feedback　is　employed　to　achieve　higher　linearity.　Furthermore,　a　matching　network　is　considered　for　input　impedance　matching.　The　active　variable　attenuator　is　simulated　and　verified　by　using　Agilent　ADS　design　kit.　The　results　indicate　that　the　gain　dynamic　range　reaches　40dB,　the　gain　flatness　is　below　3　dB,　the　S11　is　lower　than　-10　dB,　voltage　standing　wave　ratio　(VSWR)　is　below　1.52dB,　and　the　input　third　order　intercept　point　(IIP3)　is　15dBm　when　the　voltage　changes　from　0.7　∼　1.8V　in　the　frequency　band　of　3.1　GHz　to　10.6　GHz.　©　2012　IEEE.