当目标飞机从图2.25左侧接近时（t<0），瞬时多普勒频移为正。
As the targetaircraft approaches from the left in Fig. 2.25 (t < 0) the instantaneousDoppler shift is positive.
当飞机与雷达平行（t=0）时，多普勒频移为零，因为速度的径向分量为零。
When the aircraft isabreast of the radar (t = 0) the Doppler shift is zero because the radialcomponent of velocity is zero.
最后，当飞机经过雷达所在的位置（t>0）时，多普勒频移将变为负值，正如对逐渐远离目标所预期的那样。
Finally, as theaircraft passes by the radar (t > 0) the Doppler shift becomes negative, aswould be expected for a receding target.
这种二次函数的距离变化在合成孔径雷达中很重要，将在第8章中进一步讨论。
This quadratic rangecase is important in synthetic aperture radar and will be revisited in Chap. 8.
相位变化历史表征了在数据采集过程中目标与雷达之间的距离变化特性。
The phase historyencodes the variation of the range between the target and radar during the datacollection time.
对于恒速运动的例子（式2.99），相位历史是对应于恒定频率正弦曲线的时间的线性函数，即恒定多普勒频移。
For theconstant-velocity example [Eq. (2.99)], the phase history is a linear functionof time corresponding to a constant frequency sinusoid, i.e., a constantDoppler shift.
对于式（2.103）的交叉目标场景示例，它是时间的二次函数，产生频率随时间线性变化的多普勒频移正弦曲线。
For the crossingtarget example of Eq. (2.103), it is a quadratic function of time, producing aDoppler shift sinusoid having a frequency that varies linearly with time.
对于其它场景的雷达-目标运动将产生其它形式的函数变化形式。
Other radar-targetmotions will produce other functional forms for the phase history.
更一般地说，相位历史这个术语可以指雷达数据的任何维上的相位变化（或相应的复指数形式）。
More generally, theterm phase history can refer to the variation of phase (or the correspondingcomplex exponential) in any dimension of the radar data.
另外两种常见的用途是描述频率或相位调制波形的快时间相位函数或在固定时间上阵列天线孔径的空间相位变化。
Two other common usesare to describe the fast-time phase function of a frequency or phase-modulatedwaveform or the spatial phase variation across the face of an array antenna ata fixed time.
我们将看到，相位变化历史是雷达信号处理的核心。
As will be seen, thephase history is central to radar signal processing.
许多重要的雷达信号处理的设计关键依赖于对采集数据的相位历史进行精确建模或估计。
The design of manyimportant radar signal processing operations depends critically on accuratelymodeling or estimating the phase history of the collected data.
这种示例包括脉冲压缩、自适应干扰消除和成像。
Examples includepulse compression, adaptive interference cancellation, and imaging.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
更多精彩文章请关注微信号：