Research On The Calibration And Error Analysis Of AC Radiometer System

Microwave radiometer has been an effective tool for passive detecting. In order to useit for quantitative measurement, we should calibrate it. The calibration of the microwaveradiometer means to reach the equation between the output voltage and the signal of input,usually means the input antenna temperature. This paper focuses on the calibrationtechnology used by domestic and foreign country, and analyses the key points involved inthe calibration process such as calibration methods, calibration model, and calibrationsource.Under the needs of the research and application in domestic, we developed a Ka-bandAC radiometer system, and introduced the calibration of the AC radiometer firstly,including the design of the calibration methods, models, and the calibration source. Thecalibration of the AC radiometer is usually implemented in two different methods: thesingle branch calibration and multi-branch calibration. In order to improve the calibrationaccuracy of AC radiometer, we model the two methods respectively, which take the branchloss and non-perfect match into account. At last we analyses the calibration equation. As itis difficult to achieve single branch calibration, so we chose the multi-branch calibrationmethod to calibrate the AC radiometer, the hot reference source we use is the noise source,cold reference is liquid nitrogen, ambient temperature calibration source is a blackbody,and we use the single-pole three-throw switch to control the input of the differentcalibration source, thereby obtaining two different temperatures so that it can realize the“two-point calibration”.This paper designed an experiment to validate the multi-branch calibration by thedeveloped AC radiometer, and obtained the following results: First, when the T Ais300K, the sensitivity of the radiometer is0.47K, better than0.5K, so it can be used forapplication. Second, the calibration accuracy is2.47K. In order to improve the calibrationaccuracy of AC radiometer, we analyze the error sources such as the parameters of thetransmission network, linearity of the receiver, the accuracy of the calibration sourcetemperature and the A/D error which contributed to the calibration accuracy.