传统ISO标准LPDA设计中数个关键参数定义及简称

传统ISO标准LPDA设计中数个关键参数定义及简称：
         一只独立频率天线的设计，
                       对数-周期双极性天线。
        由于实际上所有的如入功率都由活跃区间辐射掉， 它的右边的较大的元件没有激励。 进一步，因为辐射是指向顶端， 这些较大的单元基本上是在一个没有场的区域内，为此不会显著影响操作。 虽然在活跃区域的左边的较短的元件是在天线射线内， 由于他们的长度较短他们对形状的影响小， 并且有180度的相移。
我们现在讨论一只对数-周期双极性阵列的设计。 我们把设计局限在计算元件的长度和间隔， 针对特定的运行带宽和发射图形的方向性。 设计参数是尺度系数τ( )，由（10.56）给出，半角α ( )在顶部相对，元件的间隔比值σ ( )对下个较长的元件的长度两倍。由于沿着结构，活跃区域不可忽略长度， 设计的阵列比设计规格有一个较大的带宽。 这个较大的带宽被称作“结构带宽”，标记为 。 的比值对设计带宽B命名为“活跃区域的带宽，” ，并且关联与σ( )和τ( )*。   
  （请见上叙内容英文如下）
   Design of a Frequency-Independent Antenna，                                                    Log-periodic dipole array
Since practically all of the input power is radiated by the active region, the larger elements to the right of it are not excited. Furtfaennore, because the radiation is toward the apex, these larger elements are essentially in a field-free region and hence do not significantly influence the operation. Although the shorter elements to the left of the active region are in the antenna beam, they have small influence on the pattern because of their short lengths，close spacings, and the 180°-phase shift.      
We shall now discuss the design of a log-periodic dipole array. We shall restrict the design to the computation of the lengths and spacings of the elements for a specified bandwidth of operation and directivity of the radiation pattern. The design parameters are the scale factor τ( )
given by (10.56), the half angle α ( )
subtended at apex, and the ration σ ( ) of the element spacing to twicw the length of the next larger element. Since the active region is not of negligible length along the structure, the array is designed for a larger bandwidth than the design specification. THis larger bandwidth is known as the ”bandwidth of the structure,”denoted Bs. The ratio of Bs to the design bandwidth B is termed the “bandwidth of the active region,” Bar and is related to σ( ) and τ( )*.  
    2019-9-23