注意式（2.77），当在频率域积分时，意味着白噪声过程中的无穷大功率。
Note that Eq. (2.77),when integrated over frequency, implies infinite power in the white noiseprocess.
然而，在实际中，噪声并不是白的[式（2.76）]，而且，在任何情况下，在任何实际系统中都只能在有限带宽上观察到噪声。
In reality, however,the noise is not white [Eq. (2.76)] and, in any event, it is observed in anyreal system only over a finite bandwidth.
当频率低于100GHz时，式（2.77）的近似值要求等效噪声温度T’（将在下文进行定义）大于约50K，这种情况几乎总是如此。
For frequencies below100 GHz, the approximation of Eq. (2.77) requires the equivalent noise temperatureT’ (to be defined below) to be larger than about 50 K, which is almost alwaysthe case.
因此，热噪声表现为一种白色的功率谱。
Consequently, thermalnoise has a white power spectrum.
对于许多实际系统，选择系统温度为“标准”温度T = 290 K = 62.3°F是合理的，因此
在相干雷达接收机中，系统前端的噪声将对正交解调后的I通道和Q通道都产生影响。
In a coherent radarreceiver, the noise present at the front end of the system contributes noise toboth the I and Q channels after the quadrature demodulation.
I和Q通道噪声都是等功率的零均值高斯随机过程。
The I and Q channelnoises are both zero-mean Gaussian random processes with equal power.
由于总噪声谱密度为kT W/Hz，因此每个通道中的噪声密度分别为kT/2 W/Hz。
Since the total noisespectral density is kT W/Hz, the noise density in each channel individually iskT/2 W/Hz.
此外，如果输入噪声的功率谱为白色，则I和Q噪声过程是不相关的，它们的功率谱也是白色的。
Furthermore, if thepower spectrum of the input noise is white, then the I and Q noise processesare uncorrelated and their power spectra are also white.
由于I和Q噪声过程是高斯且不相关的，因此它们之间也是相互独立的。
Since the I and Qnoise processes are Gaussian and uncorrelated, it follows that they are alsoindependent (Papoulis and Pillai, 2001).
接收机各组件的带宽各不相同，但最窄的带宽通常约等于发射脉冲的带宽。
The bandwidths of thevarious components of a receiver vary, but the narrowest bandwidth is generallyapproximately equal to the bandwidth of the transmitted pulse.
如果接收机中包含的组件带宽比接收信号的带宽更窄，能量就会损失，从而降低灵敏度。
If the receivercontains any component of narrower bandwidth signal, energy will be lost,reducing sensitivity.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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