Research On Mechanism Of Gyromagnetic Nonlinear Effect In High-power Microwave Electromagnetic Environment

The high-power microwave(HPM)electromagnetic environment is characterized by a high-peak power and narrow pulse width.The most important application of HPM in the military is a directed energy weapon,that is,via the antenna to the target electronic system radiation high-power electromagnetic pulse signal,through the front-door path(microwave signal channel)or the back-door path(cavity holes,slits,interconnecting cables,etc.),and other coupling channels into the internal electronic system,causing interference,disruption,degradation and destruction and other effects.Power limiting is an important front-door protection method against HPM.Compared to the solid-state circuit limiting and waveguide plasma limiting,ferrite limiters based on intrinsic material properties inherently have the advantage of high-peak-power capacity.However,the classical gyromagnetic nonlinear effect theoretical model cannot be directly applied to the narrow-pulse electromagnetic environment.This is because the traditional model implies the continuous-wave steady-state conditions and cannot characterize waveform parameters such as high-peak-power,narrow pulse width,and low rising-edge time,which are the key concerns of the HPM electromagnetic environment.In view of this,in order to accurately grasp the threshold and loss response principle of gyromagnetic nonlinear effect under microwave narrow pulse excitation.The dissertation starts from the fundamental physical processes of classical gyromagnetic nonlinear effects and explores the excitation and control mechanisms of transient electromagnetic environments in terms of theoretical derivation,electromagnetic simulation,and high-power experiments.Following that,it provides a scientific basis for ferrite limiting protection technology based on gyromagnetic nonlinear loss effects in the HPM electromagnetic environments.The specific research is as follows:1.based on the classical threshold theory of gyromagnetic nonlinear effects,the dissertation starts from the fundamental physical process in that the half-frequency spin waves coupled with radio frequency(RF)magnetic field energy overcome their damping and grow in an unstable process under parallel-pumping conditions.The critical state of RF magnetic field energy loss caused by transient electromagnetic wave excitation spin wave instability process is analyzed.The coupling relationship between the halffrequency spin waves and the transient alternating magnetic field is established by the transient electromagnetic wave exciting the spin-wave instability process that causes the critical state of RF magnetic field energy loss.This leads to the derivation of an improved critical-threshold model of the gyromagnetic nonlinear effects with the ability to characterize microwave pulse parameters(pulse width,and the rising-edge time).Secondly,based on this threshold model,a theoretical analysis of the butterfly curve characteristics,i.e.,the trend of the threshold response of gyromagnetic nonlinear effects caused by different intrinsic characteristics of "half-frequency" spin waves characterized by the applied magnetic field parameters under the excitation conditions of the narrowand long-pulses microwave.2.Based on the above improved threshold model,an equivalent electromagnetic simulation method suitable for the device-level gyromagnetic nonlinear loss is proposed by introducing the idea of equivalent simulation.This method converts the gyromagnetic nonlinear loss model based on transient threshold response into equivalent magnetic loss tangent parameter,so that the nonlinear loss response simulations can be performed with the help of commercial three-dimensional(3D)electromagnetic simulation software.It provides a simulation approach for the design of the HPM limiter based on the transient gyromagnetic nonlinear effects.3.To verify the effectiveness of the improved theory and simulation method in the dissertation,The X-band HPM pulse injection experimental platform with variable pulse width and variable rising-edge time is constructed.Focus on microwave pulse waveform parameters(pulse width,the rising-edge time,power,etc.)and different applied magnetic field parameters on the threshold and power loss response characteristics of gyromagnetic nonlinear effects.Theoretical calculations and experiments show that the nonlinear effect threshold and loss responses of polycrystalline Yttrium Iron Garnet(YIG)uniform microstrip transmission line structure under microwave narrow pulse excitation are highly correlated with microwave pulse waveform parameters.The gyromagnetic nonlinear effect threshold of the YIG microstrip decreased from tens of watts to less than 10 watts and showed roughly energy threshold characteristics under the excitation of the microwave signals with a pulse width 40 ns to 100 ns.However,when the microwave pulse width is greater than 400 ns,the response presents the power threshold characteristics.When the input power is 420 W,the highest power loss of YIG microstrip is 16 dB.In addition,the butterfly curve of threshold responses of nonlinear effect in YIG microstrip under different external magnetic fields shows that the thresholds on the left side of the butterfly curve increase with the increasing applied magnetic field under the microwave narrow pulse excitation.However,the thresholds decrease with the increasing bias magnetic field under the long-pulse conditions.The calculation and equivalent simulation results based on the improved threshold model in the dissertation are consistent with the experimental data,which verifies the effectiveness of the improved threshold model and equivalent simulation method.4.To further reduce the threshold level of the gyromagnetic nonlinear effect excited by the HPM signal and enhance the nonlinear loss performance(limiting isolation).The dissertation starts from the idea of using microwave resonant structure to enhance the coupling between spin waves and RF magnetic field to realize the time-domain and power-domain limiting protection based on the nonlinear effect.Meanwhile,the linear response of the ferrite material is combined to integrate the frequency-domain protection.As a result,a parallel-coupled microstrip bandpass filtering-limiting structure based on the polycrystalline YIG material is constructed.Simulation and experimental results show that the device has a center frequency of 9.6 GHz,a bandwidth of 400 MHz,and the stopband inhibition reaches more than 30 dB at 8.5 GHz and 11 GHz.In the range of microwave pulse width from 30 ns to 200 ns,the minimum limiting-threshold level of the protection device is 21.7 dBm,and the maximum limiting isolation reaches 33.8 dB when the input power is 62 dBm.5.In addition,a waveguide low-pass filtering-limiter circuit structure with wide rejection band characteristics is also proposed in this dissertation to meet the requirements of higher power protection applications.The stopband of the device is broadened by the transmission poles spacing distribution method,and the HPM limiting protection is realized by loading YIG material.The small-signal simulation and experimental results show that the out-of-band harmonic suppression range is more than four times of the TE10 mode cutoff frequency of the input waveguide port.The time-domain and powerdomain limiting simulation results show that the minimum limiting-threshold level of the protection device is 58.1 dBm,and the maximum time amplitude isolation reaches 26.7dB when the input power is about 68.57 dBm in the range of 30 ns～200 ns microwave pulse width.