Determine the physical mechanism and source region of beat wave modulation by changing the frequency of high-frequency waves

This paper introduces a new approach for the determination of the source region of beat wave(BW)modulation.This type of modulation is achieved by transmitting high-frequency(HF)continuous waves with a frequency difference f,where f is the frequency of modulated ELF/VLF(extremely low frequency/very low frequency)waves from two sub-arrays of a high power HF transmitter.Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency,there exists a controversy on the physical mechanism of BW and its source region.In this paper,the two controversial theories,i.e.,BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously.According to the analysis and simulation results presented in this paper,it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions.Therefore,this characteristic can be utilized as a potential new approach to determine the physical mechanism and source location of BW.

双频双波束加热电离层激发甚低频/极低频辐射理论分析

基于高电离层质动力非线性加热理论,引入差频双波束概念,建立双频双波束加热电离层激发甚低频/极低频(VLF/ELF)辐射理论仿真模型,通过对已有实验参数进行仿真计算,验证了模型的正确性.据此模型,全面分析了不同纬度、有效辐射功率、加热频率、极化模式、频率差、实验时段等对激发VLF/ELF辐射强度的影响,并对比分析了中低纬度地区双频双波束和幅度调制两种方法激发VLF/ELF信号的差异.分析结果表明:VLF/ELF辐射效果随着地磁倾角的增加而增强,随着系统有效辐射功率的增大而增强;X波模式优于O波模式;实验时段冬季最好,夜晚优于白天;加热频率和频率差存在最优值选取问题.对于背景自然电流较弱的中低纬度地区,相对现有幅度调制方法,利用双频双波束方法激发VLF/ELF辐射更加有效,两者相差10 d B以上.