Research And Analysis On Passive Intermodulation Characteristics Of RF Devices In Satellite Communication

Large bandwidth,large capacity,and multi-carrier are the inevitable trend of satellite communication towards the development of satellite Internet.However,in multi-carrier satellite communication systems with ultra-large transmission power and extremely high sensitivity,the phenomenon of passive intermodulation(PIM)generated by passive RF devices at high power of multi-carriers is becoming increasingly prominent.PIM has become a major obstacle restricting the development of satellite communication systems towards greater bandwidth,higher power,and greater capacity.However,the current research on PIM has shortcomings such as too ideal PIM modeling,inaccurate PIM suppression,and so on.In order to better suppress PIM in satellite communication systems and improve system performance,Thesis starts from the perspective of the generation mechanism of passive intermodulation and its nonlinear characteristics,the generation mechanism of passive intermodulation in radio frequency components and PIM suppression methods in satellite communication systems have been studied.The specific work is as follows:1.Based on the equivalent GW model of metal contact,an equivalent circuit model of electrical contact is established.Aiming at the RF connection components commonly used in satellite communication systems,such as rectangular waveguides and coaxial connectors,a PIM calculation model of metal contact surfaces is established.The effects of surface parameters,contact pressure,roughness,film thickness,and temperature on the PIM levels of coaxial connectors and rectangular waveguides are analyzed,and different structures are compared the PIM levels of different types of connectors and different metal conductors are comprehensively analyzed,including the characteristics of RF device PIM and the impact of interference.2.Based on the satellite spread spectrum communication system,a PIM model excited by spread spectrum signals is established,and the impact of different input power and spread spectrum bandwidth on PIM is analyzed.The impact of PIM on the spectrum of the satellite communication system for suppression and demodulation is studied.The PIM levels under different contact conditions excited by BPSK(10)spread spectrum signals,BPSK modulated signals,and single frequency signals are compared and analyzed.3.Based on the PIM interference model of satellite spread spectrum communication,a PIM reference signal is established to suppress PIM from the perspective of digital signal processing.Firstly,FFT is used to estimate and compensate for the frequency offset of the PIM signal.Secondly,referring to the delay between the PIM and the actual PIM,the minimum mean square algorithm is used to adaptively estimate the channel impulse response of the PIM,making the PIM estimation more accurate.The error rate simulation results show that this method can increase the error rate gain by more than 10 d B,verifying the effectiveness of the PIM cancellation scheme.The analysis and modeling of the PIM mechanism and signal characteristics of radio frequency connecting devices in satellite communication systems in thesis can provide reference for the design and use of low PIM radio frequency connectors,provide a certain basis for the PIM research and prediction of broadband signals,help guide the suppression of PIM in satellite communication systems,and provide reference value for the design and development of high-power,ultra-wideband modern satellite communication systems in China.At the same time,This research can also be extended to applications in mobile communication,base station communication,and other systems.