【读书2】【2014】基于MATLAB的雷达信号处理基础（第二版）——分布式目标的距离方程(4)

现在假设发送一个距离分辨率为ΔR的脉冲，如图2.2所示。

Now suppose a pulse of range resolution ΔRis transmitted as shown in Fig. 2.2.

Figure 2.2. 在斜距R0和掠射角δ的情况下，将距离分辨率投影到水平面上Projection of range resolution onto a horizontal plane at a slantrange R0 and grazing angle δ.

无论天线脚印的覆盖面积如何，分辨率单元内散射体的距离范围都是ΔR/cosδ米。

Regardless of the antenna footprint, therange extent of scatterers within the resolution cell, and thereforebackscattering energy at any instant, is ΔR/cosδ meters.

散射体不会对接收到的信号产生明显的影响，除非它们都被照射（这样会有一些后向散射）并且处于天线主瓣内（这样它们的后向散射就不会明显减弱）。

Scatterers will not contributesignificantly to the received signal unless they are both illuminated (so thatthere is some backscatter) and within the mainlobe of the antenna (so thattheir backscatter is not significantly attenuated).

因此，分辨率单元的有效下视距离范围是距离分辨率和俯仰角波束宽度中较小的一个，因为它们都被投影到散射表面上。

Consequently, the effective down-rangeextent of the resolution cell is the lesser of the range resolution and theelevation beamwidth as each is projected onto the scattering surface.

根据距离、距离分辨率和掠射角的相对值，两者都可能是限制因素。

Depending on the relative values of range,range resolution, and grazing angle, either could be the limiting factor.

如果由距离分辨率限制有效范围，则称分辨率单元是脉冲限制的；如果主瓣区域大小是限制因子，则称为波束限制。

If the range resolution limits theeffective extent, the resolution cell is said to be pulse limited; if themainlobe extent is the limiting factor, it is said to be beam limited.

这两种情况如图2.3所示。

These two cases are shown in Fig. 2.3.

Figure 2.3. 天线波束脚印和脉冲包络的相对几何关系：（a）波束限制情况和（b）脉冲限制情况Relative geometry of antennafootprint and pulse envelope: (a) beam-limited case and (b) pulse-limited case.

这两种情况之间的判断条件如下：

The boundary between the two cases isobtained by equating the pulse length and elevation beam extents as projectedonto the ground plane to see which is shorter:

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

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