雷达的典型噪声系数可以低至2或3分贝，也可以高至10分贝或更高。
Typical noise figuresfor radars can be as low as 2 or 3 dB, and as high as 10 dB or more.
相应的有效温度范围在170 K到2600 K之间。
Correspondingeffective temperatures range from about 170 K to over 2600 K.
在第2.2节中，术语“雷达距离方程”适用于方程（2.11）、（2.25）、（2.30）和（2.32）。
In Sec. 2.2, the term"radar range equation" was applied to Eqs. (2.11), (2.25), (2.30),and (2.32).
这些表达式描述了在各种系统和传播条件下雷达接收到的回波功率。
These expressionsdescribed the echo power received by the radar given various system andpropagation conditions.
如第6章所述，雷达的探测性能并不取决于接收功率本身，而是取决于探测点的信噪比。
As will be seen inChap. 6, the detection performance of a radar depends not on the received powerper se but on the SNR at the point of detection.
式（2.83）可用于将功率距离方程转换为信噪比距离方程。
Equation (2.83) can beused to convert the power range equations to SNR range equations.
为了说明这一点，考虑点目标距离方程[式（2.11）]，该方程表示接收机输入端有用信号的功率Pr。
To illustrate,consider the point target range equation [Eq. (2.11)], which expresses thepower Pr of the signal available at the input to the receiver.
只要信号带宽全部位于接收机带宽Bn之内，则接收机输出的信号功率为P0 = GsPr。
The signal power atthe output will be P0 = GsPr provided thesignal bandwidth is entirely contained within the receiver bandwidth Bn.
根据式（2.83），输出噪声功率为No= kT0βnFnGs。
From Eq. (2.83), theoutput noise power is No = kT0βnFnGs.
因此SNR为
The SNR is therefore
式（2.84）中的最后一个表达式给出了信噪比与发射机和接收机特性、目标RCS、距离和损耗因子之间的关系。
The last expressionin Eq. (2.84) gives the SNR in terms of transmitter and receivercharacteristics, target RCS, range, and loss factors.
通过修改体散射和面散射的式（2.25）、（2.30）和（2.32），可以类似的方式获得信噪比的表达式。
Modifications of Eqs.(2.25), (2.30), and (2.32) for volume and area scatterers to express them interms of signal to noise ratio are obtained in the same manner by simplyincluding the quantity kT0βnFn in theirdenominators.
式（2.84）表示接收机输出端的信噪比，即信号处理之间的信噪比。
Equation (2.84)represents the SNR at the receiver output, but prior to any signal processing.
本书所讨论的大多数技术要点是通过信号处理手段提高式（2.84）的信噪比，以获得更好的检测、测量和成像结果。
The point of most ofthe techniques discussed in this text is to increase the SNR above that valuethrough signal processing means so as to obtain better detection, measurement,and imaging results.
信号处理对信噪比的影响可以通过简单地在距离方程中添加信号处理增益项Gsp来建模：
The impact of signalprocessing on the SNR can be modeled by simply adding a signal processing gainterm Gsp to the range equation:
在随后的章节中，Gsp将以特定技术的参数表示，如匹配滤波和多普勒处理。
In ensuing chapters,Gsp will be expressed in terms of the parameters of specifictechniques such as matched filtering and Doppler processing.
与式（2.11）一样，式（2.85）也常被称为雷达距离方程。
Like Eq. (2.11), Eq.(2.85) is also often called the radar range equation.
在本书的其它章节中，术语“距离方程”或“雷达距离方程”通常指式（2.85）的信噪比形式及针对体/面积散射体的情况。
In the remainder ofthis text, the term “range equation” or “radar rangeequation” usually refers to the SNR form of Eq. (2.85) and its analoguesfor volume and area scatterers.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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