Stability Analysis of an SiGe HBT-Based Active Cold Load

In this study, we report the results of short- and intermediate-term stability at L-band of an active cold load (ACL) realized with an SiGe heterojunction bipolar transistor. A noise injection radiometer has been developed to perform the measurements. A noise-equivalent delta temperature of less than 40 mK and a stability estimated to 30 mK during 90 s were obtained from Allan variance analysis. The results indicate that the variations of the ACL noise temperature correspond to the sensitivity of the measurement system. No drift was detected over one week of continuous characterization indicating that this kind of active load is very stable.