穿越电离层双程传播法拉第旋转的理论分析

Theoretical analysis of Faraday rotation for trans-ionosphere two-way propagation

对于双程传播,考虑目标的散射系数,利用多波模合成概念,导出了包含法拉第旋转角(Ω)的波场的表达式。波场仍分为两部分,一部分,因法拉第旋转角相互抵消,而不受影响,即寻常波。另一部分,波的相位以2Ω为参数,波的的振幅以4Ω为参数,而受到法拉第旋转的影响,即非常波。当工作频率低于1000MHz时,法拉第旋转的影响,是严重的。一般说来,双程法拉第旋转角并非小量级,而且是以简谐函数出现,难于总结简明规律。如果,散射系数随入射波偏振的不同而改变,那么,两部分波所受到的影响将更为复杂,如结论所示。

Considering the scattering coefficient of target, the expression of wave field containing Faraday rotation angle for two-way propagation is derived by using concept of multi-mode combination. The wave field is still divided into two parts. One part is not effected by Faraday rotation, because of cancellation of rotating angels for two oppositing polarized waves, so it is called as ordinary wave. The another part is effected with parameters of four times rotating angle on the amplitude and of two times rotating angle on the phase respectively, then it is called as extraordinary wave. As the operating frequency is below about 1000MHz, Faraday rotation effect is serious. In typical condition, Faraday rotation angle is not small, and which is with harmonic function to effect the wave field, then, it is difficult to summarize some simplified rules. If the scattering coefficients are different for different polarized incident waves, the conditions are more complicated as shown in the conclusions.