| The electromagnetic pulse weapons have appeared in modern warfare,which greatly threaten the survivability of RF receivers such as satellite navigation,radar and wireless communication systems.The RF front-end circuit is the first module to process satellite signals,the threat is more prominently.Especially,the performance of low noise amplifier in RF front-end circuit directly affects operation of the whole navigation receiving system.Therefore,in order to improve the equipment's ability to resist electromagnetic damage,it is of great significant to study the coupling process of electromagnetic pulse to satellite navigation receiver.Aiming at the damage effect of electromagnetic pulse on receiver,this thesis studies it by combining theory,simulation and experiment.Firstly,three common electromagnetic pulses,high-altitude nuclear electromagnetic pulse(HEMP),ultra wideband pulse(UWB)and high power microwave(HPM)are introduced,and their time domain and frequency domain characteristics are analyzed.The ground killing region and energy propagation formula are analyzed from explosion height,explosion dip angle and beam angle.The damage paths of electromagnetic pulse to the electronic target are listed,and the electromagnetic pulse effect is described from two aspects of the system and the physical mechanism.Then,antenna coupling and slot coupling of the receiver are simulated and analyzed.Aiming at antenna coupling,a patch antenna used for satellite navigation is designed in the electromagnetic simulation software.Radiation simulation of antenna is carried out by three kinds of electromagnetic pulses which are analyzed above.The coupling effect is analyzed.Simulation results show that the HEMP's energy is concentrated below 200MHz,the coupling effect to navigation antenna is general;UWB pulse is very wide in spectrum,the energy distribution sparse in the unit frequency band,so the coupling effect is also general;The coupling effect of HPM is closely related to its frequency,the curve fitted by coupling effect and frequency shows a "bell" curve distribution.For slot coupling,we establish the cavity model and obtain some resonant frequency points,and analyze the error with the theoretical values.The results show that the shielding effectiveness of the metal cavity drops sharply at these frequency points and nearby.Then the RF front-end model and low noise amplifier(LNA)model of the satellite navigation receiver are built on the circuit simulation software.The interference signals obtained by electromagnetic simulation are injected into the RF front-end model and the LNA model.From the simulation results,it can be seen that a small amount of energy in the system will still reduce the performance of the circuit,resulting in LNA working in the nonlinear region.As long as the coupling energy of slot coupling is small,LNA's noise coefficient will be greater than 1,which has not met the needs of low noise,resulting in the performance degradation of the whole receiving system.Finally,in order to verify the simulation results,the radiation and injection experiments are carried out.The double exponential pulse radiation experiment is used to obtain antenna coupling law.At the same time,the performance degradation of LNA under interference is studied by injecting experiment.The experimental results show that,no matter antenna coupling or slot coupling,a small amount of coupling energy will affect the normal operation of the receiver.The experimental results verify the simulation results well. |
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