Research on K-band Receiver Noise Calibration Based on Chopper Wheel Technology

The receiver is an important device for detecting weak radio signals in radio astronomy. The amplitude calibration of the receiver is to convert the response of the receiver for radio source into the flow density in astronomy. The conventional method is to convert the amplitude response of the receiver itself into an equivalent temperature value using the classical cold and ambient load method, and then further calibrate the radio source. The K-band receiver amplitude calibration platform based on the chopper wheel technology is built, and the noise temperature of the K-band normal temperature receiver is tested by the chopper wheel method, and compared with the test results of the conventional cold and ambient load method. From the results, under the fine weather conditions, the maximum test error of the noise temperature at the 30^\circ and 90^\circ elevation is 7.5% and 8.4%, which can be well applied to the actual noise temperature test; but at the 5^\circ elevation test, the ground noise was introduced due to the low elevation angle, so the test error of the chopper wheel method was increased to about 20%--30% and could not be used. This paper also hopes to further develop the theoretical calculation and actual measurement of the K-band sky brightness temperature on this basis, so as to improve the application of the chopper wheel technology, so that it can satisfy the noise calibration test requirements under different meteorological conditions.