电离层Es对HF和VHF传播信号的影响

Es层是存在于电离层中的电子密度非常高的偶发E层（Sporadic E），其电子密度可达常规E层的100倍.电离层Es能够反射原本穿透F层的VHF低频段（30~150MHz）无线电波，而且对HF高频段（10~30MHz）无线电波传播具有显著影响.运用垂测和斜测观测数据，研究HF频段Es层电波传播特征，得到了不同类型及不同高度Es层的衰减系数.根据f₀E_s的日变化规律，可得HF频段衰减系数的日变化规律，进而分析并得到Es层对短波传播的影响.不存在电离层Es时，通常无法通过电离层实现VHF超远距离通信.为了对VHF链路通过电离层Es的传播衰减进行定量分析，根据EBU多条链路的观测结果，拟合并建立了电离层Es衰减模型.将该模型、ITU模型和观测数据进行对比，发现本文建立的模型准确度更高.利用建立的模型，对电离层Es不同临频f₀E_s条件下接收信号场强和电压随传播距离的变化进行了计算，结果可为VHF链路设计及建立提供参考. 

Influence of Ionospheric Sporadic E on Radio Propagation in HF and VHF Band

The Es layer is a sporadic E layer in the ionosphere, and its electron density can reach 100 times more than normal E layer. The Es layer can reflect radio waves in VHF (30~150MHz) band, and it has a significant impact on radio wave propagation in high HF (10~30MHz) band. In this paper, the observation data of the vertical and oblique ionospheric sounders is used to study the propagation characteristics of HF band radio waves in the Es layer. The attenuation coefficients of different types and altitudes of Es layer are obtained. According to the daily variation of f₀E_s, the diurnal variation of attenuation coefficient in HF band is obtained, and then the influence of Es layer on shortwave propagation is analyzed. In the absence of the ionospheric Es layer, it is not possible to achieve long-range VHF communication by the ionosphere. In order to quantitatively analyze the propagation attenuation of the VHF link by the Es layer, the ionospheric Es layer attenuation model is constructed by fitting the observation data of the European Broadcasting Union (EBU) links. The model and ITU (International Telecommunication Union) model are compared with the observed data. The results show that the model established in this paper is more accurate than ITU model.