Modulated waveforms for harmonic minimization of far-field signals in amplitude-modulated heating of the ionosphere  

作　　者：ZhiJian Lu Yong Li Hui Li Jian Wu JingFeng Yao XingBao Lyu ChengXun Yuan ZhongXiang Zhou Ying Wang 

机构地区：[1]School of Physics,Harbin Institute of Technology,Harbin 150001,China [2]China Research Institute of Radio Waves Propagation,Beijing 102206,China [3]Heilongjiang Provincial Key Laboratory of Plasma Physics and Application Technology,Harbin 150001,China [4]Heilongjiang Provincial Innovation Research Center for Plasma Physics and Application Technology(International Cooperation),Harbin 150001,China

出　　处：《Earth and Planetary Physics》2025年第2期387-399,共13页地球与行星物理(英文版)

基　　金：supported by the National Key R&D Program of China (No. 2022YFE0204100);the National Natural Science Foundation of China (12205067 and 12375199);the Fundamental Research Funds for the Central Universities (Grant No. HIT.OCEF. 2022036)。

摘　　要：This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radiation source. We consider various modulation waveforms and find that square-wave modulation has the highest excitation efficiency for ELF/VLF signals, and that square-wave modulation with a smaller duty cycle(<50%) exhibits higher excitation efficiency for ELF/VLF signals, while the sin^(2)t waveform modulation yields the lowest proportion of harmonic energy in the generated signals. The amplitude of the second harmonic generated by the sin^(2)t waveform is less than one-tenth that of the fundamental frequency, and the energy of higher-frequency harmonics can be negligibly small compared with those of the fundamental wave. It is a challenging task to achieve a balance between enhancing the excitation efficiency of ELF/VLF signals and also suppressing harmonics generated by the modulated heating process. This is because the harmonics are correspondingly enhanced as the excitation efficiency of the signals is increased. However, we find that under conditions of varying effective radiant power and modulation frequency, as long as the modulation waveform is unchanged, the energy ratio between the fundamental frequency signal generated by modulated heating and each harmonic is relatively fixed, with changes only in signal intensity and the location of the radiation source zone. This implies that one can first select modulation waveforms that make the signal less prone to distortion, then increase the effective radiated power to enhance the signal strength, without concern for harmonic interference of the fundamental signal.

关 键 词：ELF/VLF HARMONIC amplitude-modulated heating modulated waveforms 

分 类 号：TN911.3[电子电信—通信与信息系统] P352[电子电信—信息与通信工程]