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天线相位中心的概念非常有用，因为它定义了天线的一个有效位置，便于分析有效路径长度、多普勒频移等等。

The phase center concept is useful becauseit defines an effective location of the antenna, which can in turn be used foranalyzing effective path lengths, Doppler shifts, and so forth.

对于对称辐射的孔径天线，相位中心位于孔径平面的中心，但可能会在真实孔径的前后移动。

For symmetrically illuminated apertureantennas, the phase center will be centered in the aperture plane, but may bedisplaced forward or backward from the actual aperture.

比如图1.5所示，天线相位中心必然位于y = 0，但x可能不为0，因为这与具体的天线形状有关。

Referring to Fig. 1.5, the phase centerwould occur at y = 0, but possibly x ≠ 0, depending on the detailed antennashape.

另一种重要的天线形式是阵列天线。

Another important type of antenna is thearray antenna.

阵列天线是由一组独立的天线集合（称为天线阵元）构成。

An array antenna is one composed of a collectionof individual antennas called array elements.

典型地，天线阵元都是相同的偶极子或其它宽方向图的简单天线。

The elements are typically identicaldipoles or other simple antennas with very broad patterns.

通常，天线阵元之间的间距是均匀的，由此构成均匀直线阵列，如图1.7所示。

Usually, the elements are evenly spaced toform a uniform linear array as shown in Fig. 1.7.

Figure 1.7. 均匀直线阵列天线的几何构型Geometry of the uniformlinear array antenna.

图1.8描述了真实阵列与孔径天线的例子。

Figure 1.8 illustrates examples of realarray and aperture antennas.

Figure 1.8. 典型阵列与孔径天线示例。（a）F/A-18战机上的裂缝相控阵天线，该天线是AN/APG-73火控雷达的重要组成部分；（b）卡塞格伦反射面天线。Examples of typical arrayand aperture antennas. (a) Slotted phased array in the nose of an F/A-18aircraft. This antenna is part of the AN/APG-73 radar system. (b) A Cassegrainreflector antenna. (Image (a) courtesy of Raytheon Corp. Image (b) courtesy ofQuinstar Corp. Used with permission.)

线性阵列的电压方向图可以通过考虑天线的接收模式来获得，而不是考虑发射模式。

The voltage pattern for the linear array ismost easily arrived at by considering the antenna in its receive, rather thantransmit mode.

假设阵列最左边的阵元作为参考点，该阵列由N个阵元组成，并且这些阵元是各向同性的全向天线（所有θ方向均为单位增益）。

Suppose the leftmost element is taken as areference point, there are N elements in the array, and the elements areisotropic (unity gain for all θ).

——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》

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