Microwave Radiometer Calibration Using Low-Noise Amplifier as Calibration Source

We present a novel method for built-in noise and gain calibration of a total power radiometer using a low-noise amplifier (LNA) as the calibration source. A terminated LNA’s biasing is varied to obtain multiple calibration points, with the novel postprocessing method accounting for both radiometer nonlinearity and unknown LNA parameters. This method allows for a built-in radiometer calibration without a calibrated resistive or diode noise source, instead using an internal thermometer measurement as a reference. The method is demonstrated by measuring a thermal load to a 24-GHz water vapor radiometer (WVR), achieving a mean error of 0.43 K over the band of interest under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$45~^{\circ } $ </tex-math></inline-formula>C ambient temperature variation. It is further shown that the calibration data can be used to estimate the radiometer’s gain to within 1.41 dB and noise figure (NF) to within 0.55 dB.