| Satellite communications play a fateful role in modern wars, and it is a challenging problem to jam the satellite communications data links. Based on the fact that multiple access communication performance can be deteriorated seriously by intermodulation products, this thesis aims to explore the most efficient jamming patterns to a satellite communication system based on-board FDMA-CWTDM conversion.After the analysis of nonlinear amplifier characteristics of TWTA, the FDMA/CWTDM satellite communications system and its anti-jamming measures including digital AGC and adaptive filter. This thesis mainly simulates and tests the jamming ability of time-frequency distribution jamming pattern to the experimental communication system. The author’s main work and contributions are as follows:1. The structure of satellite transponder is discussed. Research on the input/output character of amplifier at end of transponder and the produce and distributing of intermodulation is made, then and a unified compensation method of that compensate amplitude and phase distortion simultaneously is given. The simulation results demonstrate that the united compensation method has good effect.2. A thorough research was undertaken with FDMA/CWTDM system and its anti-jamming measures. Jamming patterns which is of high randomness in time-frequency domain, high peak power were designed. The simulation of digital optimal parameters filter under MATLAB platform is completed. Through the simulation of the whole system, the optimal parameters for the time-frequency distribution jamming pattern were found out.3. Based on the previous design of FPGA, The optimal time-frequency jamming pattern interference effect was obtained by optimizing the algorithm and debugging the parameters. And then the system is successfully debugged by means of intermediate frequency connection. The developed system has passed comprehensive interference test, the experimentations verified the performance of jamming patterns. |
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