Study Of The Coupling Effects Of Microwave Amplifier Under Strong Lightning Radiation

Microwave amplifier, one of the indispensable components in many electronic systems, plays the important role to amplify input small signal when it was used as the preamplifier. However, electronic systems are increasingly sensitive to transient electromagnetic phenomena, and the problems on security, reliability and EMC (Electromagnetic Compatibility) are getting more and more serious. Lightning is one of the important transient electromagnetic phenomena, and the concomitant electromagnetic pulse is a severe natural electromagnetic interference source, so the harmful coupling effects of LEMF (Lightning Electromagnetic Fields) have been attached great addition. Study shows the possibility of electronic receiver to couple considerable lightning electromagnetic energy under lightning radiation circumstance, and in this instance the strong nonlinearity behavior makes against the normal operation of microwave amplifier generally under small-signal condition.Supposing that electronic receiver have coupled considerable lightning electromagnetic energy, the coupling effect of a microwave GaAsFET amplifier in microstrip circuit configuration is studied in this thesis. Firstly, the nonlinear coupling effects of the microwave amplifier are analyzed. In this course, the state equations of the microwave amplifier adopting Curtice-3 nonlinear model under large-signal condition are built and resolved under different circumstance that positive coupling exists or not. Meanwhile, the relation between drain-source currentof GaAsFET and positive coupling electromagnetic energy is researched. The result shows that if the coupling lightning electromagnetic energy is less than the threshold of energy that can directly disable the amplifier, when positive coupling didn't exist, the amplifier may still work normally. On the contrary, if the existent positive coupling energy exceeds the threshold, the nonlinearity response of the microwave amplifier under large-signal condition in company with positive coupling would result in the mutation phenomena of drain-source current of GaAsFET, which may provide a reasonable interpretation for relative small lightning electromagnetic energy to make the microwave amplifier out of action and even be burnt out.In this thesis, the space electromagnetic coupling path and coefficient in the microwave amplifier are analyzed and calculated too. We numerically simulate the mutual coupling between the microwave amplifier and electromagnetic radiation of different frequencies by the aid of FDTD method (Finite-Difference Time-Domain Method). And as a case, the voltage coupling coefficients from output port to input port of a circuit which is composed of two branches of microstrip are calculated by boundary condition too. It shows that there is obvious space electromagnetic coupling phenomena under electromagnetic radiation of different frequencies. The relation between frequency of electromagnetic radiation and voltage coupling coefficient is nonlinear, and the voltage coupling coefficient comes to the top when the frequency of electromagnetic radiation equals to a certain value.The studies in this thesis are more important for an in-depth study of the nonlinearity response of microwave amplifier and can direct to avoid microwave amplifier out of action under strong lightning radiation.