electrical length——————————————————————————–electrical length: 1. Of a transmission medium, its length expressed as a multiple or submultiple of the wavelength of a periodic electromagnetic or electrical signal propagating within the medium. Note 1: The wavelength may be expressed in radians or in artificial UNITS of angular measure, such as degrees.Note 2 : In both coaxial CABLES and OPTICAL fibers, the velocity of propagation is approximately two-thirds that of free space. Consequently, the wavelength will be approximately two-thirds that in free space, and the electrical length, approximately 1.5 times the physical length. 2. Of a transmission medium, its physical length multiplied by the ratio of (a) the propagation time of an electrical or electromagnetic signal through the medium to (b) the propagation time of an electromagnetic wave in free space over a distance equal to the physical length of the medium in question. Note: The electrical length of a physical medium will always be greater than its physical length. For example, in coaxial CABLES, distributed resistances, capacitances and inductances impede the propagation of the signal. In an OPTICAL fiber, interaction of the lightwave with the materials of which the fiber is made, and fiber geometry, affect the velocity of propagation of the signal. 3. Of an antenna, the effective length of an element, usually expressed in wavelengths. Note 1: The electrical length is in general different from the physical length. Note 2: By the addition of an appropriate reactive element (capacitive or inductive), the electrical length may be made significantly shorter or longer than the physical length.电长度电长度：1.对于传输媒介，它的长度被表示为一个在媒介中传波的电或者电磁信号波长的倍数。注释 1：波长可能用弧度来表示，或者其它的角度单位来表示，如角度。注释 2：在同轴电缆和光纤中，传输速率大约为自由空间中的2/3。因此，波长 大约为自由空间中波长的2/3，而电长度则大约为物理长度的1.5 倍。2.对于传输媒介，（电长度）用 它的物理长乘以 电或电磁信号在媒介中的传输 时间（时间为a）与 这信号在自由空间中通过跟媒介物理长度一样的距离时所 需的时间（时间为b）的比（即电长度=物理长度*a/b） 来考虑。注释：对于一个物理媒介来说，它的电长度总是大于它的物理长度。例如，在同 轴电缆中，分布电阻、电容、电感阻碍了信号的传输；在光纤中，光波与 光纤材料之间的相互作用，以及光纤的几何结构，影响了信号的传输速率。3.对于天线，天线的有效长度常表示为波长的倍数。注释 1.电长度跟物理长度通常是不一样的。注释 2.通过增加一个适当的电抗元件（电容或电感），电长度可以显著的短于或者长于物理长度。
电长度定义：传输线的物理长度与传输波长（在传输线中）的比值
电长度物理意义：举个例子吧：物理长度为1m的传输线，对于波长分别为10cm和1cm的两个电磁波，电长度分别为10和100，也就是说：在一米的传输线上波长为10cm的波变化了10个周期，而波长为1cm的波变化了100个周期。可见：相同物理长度上波变化越频繁电长度越大！
即电长度是用来描述电磁波波形变化频繁程度的物理量