A flat gain and higher linearity UWB active variable attenuator

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.