实际上，这与用于信号处理（例如数字滤波器设计）中旁瓣控制的窗口或加权函数没有不同，峰值旁瓣可以容易地降低到大约25到40dB，但是以增加主瓣宽度为代价的。
In fact, this is no different from thewindow or weighting functions used for sidelobe control in other areas ofsignal processing such as digital filter design, and peak sidelobes can easilybe reduced to around 25 to 40 dB at the expense of an increase in mainlobewidth.
实现较低的旁瓣是有可能的，但是由于制造缺陷和固有的设计限制，在实际设计中却是很难实现。
Lower sidelobes are possible, but aredifficult to achieve due to manufacturing imperfections and inherent design limitations.
在实际使用中通常省略式（1.9）中的常数因子0.89，这样可以粗略估计出均匀辐射孔径的3-dB波束宽度约为λ/Dy弧度。
The factor of 0.89 in Eq. (1.9) is often dropped, thus roughlyestimating the 3-dB beamwidth of the uniformly illuminated aperture as just λ/Dyradians.
事实上，这是4dB的波束宽度，但是由于实际中的孔径加权扩展了主瓣宽度，因此，这是一个很好的工程经验法则。
In fact, this is the 4-dB beamwidth, butsince aperture weighting spreads the mainlobe it is a good rule of thumb.
天线功率增益G是指在相同的输入功率条件下，天线的峰值辐射强度与从无衰减、各向同性(全向)天线观察到的辐射强度的比值。
The antenna power gain G is the ratio ofpeak radiation intensity from the antenna to the radiation that would beobserved from a lossless, isotropic (omnidirectional) antenna if both have thesame input power.
功率增益是由天线方向图和天线损耗决定的。
Power gain is determined by both theantenna pattern and by losses in the antenna.
典型天线的一个有用的经验法则是
A useful rule of thumb for a typicalantenna is (Stutzman, 1998)
典型的雷达天线从宽扇形搜索波束的约10dB增益到可用于搜索和跟踪的笔形窄波束的约40dB增益。
Though both higher and lower values arepossible, typical radar antennas have gains from about 10 dB for a broadfan-beam search antenna to approximately 40 dB for a pencil beam that might beused for both search and track.
有效孔径Ae是用于描述接收天线性能的一个重要特征。
Effective aperture Ae is animportant characteristic in describing the behavior of an antenna being usedfor reception.
如果电磁波以功率密度W W/m2入射到天线上，作用在天线负载上的功率为P，则有效孔径定义为：
If a wave with power density W W/m2 is incident on theantenna, and the power delivered to the antenna load is P, the effective aperture is defined as the ratio (Balanis, 2005)
Thus, the effective aperture is the area Aesuch that, if all of the power incident on the area was collected and deliveredto the load with no loss, it would account for all of the observed power outputof the actual antenna.（感觉这句话没有翻译的必要！！！）
注意：Ae并不是天线的真实物理孔径的面积。
Note, however, that Ae is notthe actual physical area of the antenna.
而是由天线接收到的入射功率密度总量决定的人为定义的面积。
It is a fictional area that accounts for theamount of incident power density captured by the receiving antenna.
有效孔径与天线指向性直接相关，因此也与天线增益和效率相关。
Effective aperture is directly related toantenna directivity, which in turn is related to antenna gain and efficiency.
对于大多数天线，天线效率几乎都差不多，有效孔径与增益之间的关系如下：
For most antennas, the efficiency is near unityand the effective aperture and gain are related by (Balanis, 2005)
天线相前（或波前）和相位中心是两个非常有用的概念。
Two more useful antenna concepts are theantenna phase front (or wave front) and phase center (Balanis, 2005; Sherman,1984).
辐射天线的相前是指场相位恒定为常数的任何表面区域。
A phase front of a radiating antenna is anysurface on which the phase of the field is a constant.
在远场条件下，至少在局部区域内，电磁波的相前通常近似为球形。
In the far-field, the phase fronts areusually approximately spherical, at least over localized regions.
天线的相位中心就是指相前曲面的中心位置。
The phase center of the antenna is thecenter of curvature of the phase fronts.
换句话说，如果将全向辐射器放置在相位中心，则产生的相前与真实使用的天线相前具有最优匹配度。
Put another way, the phase center is thepoint at which an isotropic radiator should be located so that the resultingphase fronts best match those of the actual antenna.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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