Passive Intermodulation Test Study Of The Feed Array In The High And Low Temperature Environments

Passive intermodulation(PIM)is a phenomenon of intermodulation products produced by multiple carriers passing through microwave passive components under high power conditions.There are many factors that can affect PIM products,and one of the most important factors is temperature.In practice,this effect can be either direct or indirect.At present,in the PIM test of antenna type of multiple satellite models,it is found that the test results at room temperature are very different from those at high and low temperatures.Therefore,a set of test system for low passive intermodulation products is urgently needed under high and low temperature conditions.In the current communication satellite,the beam range of the antenna subsystem is wide and the signal strength is strong.So the satellite antenna needs to work in the form of feeding array that puts forward a new requirement for the passive intermodulation test of the antenna subsystem,namely the passive intermodulation test for the feeding array under high and low temperature conditions,to ensure the satellite under the extreme temperature variable state in space working effectively.In view of the above problems,in this thesis,we primarily study the S-band antenna feed of a satellite type.Based on in-depth analysis of the generation mechanism of PIM,the only high and low temperature passive intermodulation testing system of S band antenna feed has been set up in our country,and the relevant passive intermodulation testing has been completed.This thesis introduces the characteristics of the S band passive intermodulation test,the common test method,the construction of the high and low temperature passive intermodulation test system and the detailed steps in the test.The key indicators of the test system during the test are also described.Then,the thesis mainly analyzes the mechanism of the two factors that affect the level of the PIM product in the S band at high and low temperatures,which is obtained during the test.The corresponding suppression measures were found and verified by the experiment as follows:Through the analysis of the mechanism and its theory of the test system connection site,the expansion and contraction of the metal contact surface in the temperature-changing environments would become the main PIM source in the high and low temperature passive inte rmodulation test.So measures include connecting the source and cable connections with low PIM connector,secure the cable with a special torque wrench and replace the TNC type cable with the 7/16 type cable to reduce the level of the test system PIM products.During the test,it was observed that the jumping of the test system PIM level occurred in the temperature-changing states,which validated the correctness of the theoretical analysis in this part.Finally,the improved test system and test method are used to test the four states of the feeding array with good results.The study results of this project provide reliable theoretical and experimental support for the high and low temperature passive intermodulation testing of the antenna feeding array products in the future.