A variable active cold noise source for calibration of medical microwave radiometer

An active cold noise source with low return loss and stable operating temperature of 288 K is presented for a microwave radiometer designed for medical application (288 K to 310 K). The noise source is based on Si-Ge Heterojunction Bipolar Transistor (HBT) and is proposed for calibration of our L-band radiometer designed for detection of thermal anomalies in the human body. The noise source is centered at 1.3 GHz with 190 MHz bandwidth for return loss less than -20 dB, 3.01 dB noise figure and variable noise temperature source for the low temperature reference (288 K - 298 K).