Research On Key Techniques Of K Band Multi Channels Radiometer Front End

Recently global climate warming leads to the frequently occurring of bad weather, real-time weather forecast and artificial weather modification have great advantage to prevent disaster. The traditional detection method is dominated by the sounding balloon, which is restricted by the time of usage and space range. Ground microwave radiometer is a new type of equipment for observing tropospheric water vapor, temperature, and cloud. It not only can make up for the deficiencies of the conventional atmospheric detection data, overcome some limitations of conventional atmospheric detection, but also can obtain the value of meteorological data in the study of atmospheric structure. It is an important means of atmospheric detection. Therefore, this thesis focuses on the key techniques of K band(22GHz~32GHz) radiometer front end-SPST(single pole single throw) switch, splitter and detector.In this thesis, the theory of total power radiometer is studied, and a multi-channel parallel scheme is proposed. The feasibility and superiority of the scheme are demonstrated. The target of each module is determined on the basis of the completion of the program and then the key devices are studied. For the measurement of these key devices, a transition from waveguide to coaxial line is designed. The two transitions are connected to each other by back to back. The measurement results show that the insertion loss is better than 0.5dB and the return loss is better than 18 dB in the frequency range of 20~34GHz. Therefore, the transition can be used to test the proposed switch and multiplexer.Calibration is a necessary step for the accurate measurement of the radiometer. The scheme is integrated with the SPST switch which is in the extraction of PIN diode parameters for broadband design to control the noise source injection. The experimental results show that the insertion loss of SPST switch is less than 0.5dB and the isolation is more than 25 dB in the range of 21GHz~33GHz.The multi-channel parallel structure is realized by a multiplexer in this thesis. A 7 channels multiplexer is constituted by six diplexers after considering the design difficulty and realizability. A bandpass filter and a lowpass filter are used to realize the wideband diplexer. The final measurement shows that the insertion loss is 0.5dB in low side of passband and is 1.6 dB in the upper frequency side.Every channel of the proposed radiometer can be detected individually by using the parallel structure. As the accurate parameters of detector diode can not be obtained, a prototype circuit is designed to extract the parameters of the diode on K band before accurate design. The detector is designed on two frequency bands to obtain the optimum performance. One detector is used by the first four channels and the other detector is used by the latter three channels. The test results show that the voltage sensitivity is better than 10000mV/mW and the tangent sensitivity is-60 dBm at the video bandwidth of 1.2kHz.