On the following , on the basis of formulas given above , three kinds of effects due to ionosphere are presented : image shift due to group delay which was caused by the difference between the group velocity and the velocity of light in the ionosphere ; image distortion due to ionospheric dispersion which can create second phase error of lfm signals ; the last , the phase perturbation caused by the irregularities of the ionosphere can reduce the coherent length and affect azimuthal resolution 文中主要研究了电离层的三种影响：信号经过电离层传播的群延迟引起的成像偏移；电离层的色散效应给线性调频信号带来二次相位误差，导致图像退化、失真；以及电离层的闪烁、湍流等不规则性引起的信号相位起伏。在此基础上，比较分析了不同波段、带宽条件下电离层的影响。
The followings were discovered in the simulations of undersized waveguide : when the pulse width of input signal , a gaussian packet , is rather wide , the output signal distorted little . a superluminal group velocity 3 . 21c was revealed when the wave packet crossing 50mm forbidden region 对凹陷波导（ undersizedwaveguide ）的模拟发现：输入脉冲宽度较大的高斯波包，模拟结果显示输出波形失真较小，经过计算得到电磁波包穿过长50mm的截止区时，电场的幅度衰减了- 41 . 5db ，群速度为3 . 21c 。
The dispersive characteristic of sws is a very important parameter of the rbwo and rtwt , other parameters such as the phase velocity , group velocity , coupling impedance can be derived from the linear dispersion relation . recently , the photonic crystal have attracted many attentions of the scientists , which has become a hot point of the research , it is also a ps 周期慢波结构色散特性是研究高功率微波器件的一个重要参量,其他重要特性如相速、群速、耦合阻抗等参量都可以从色散关系衍生出来,准确,快速获得周期电磁结构的色散特性就显得尤为重要。
