图2.14描述了频率捷变导致的RCS变化问题。

Figure 2.14illustrates the ability of frequency agility to force RCS variations.

Figure 2.14. 从固定不变的视角观察，频率捷变带来的RCS变化Variation in RCS due to frequencyagility for a constant viewing angle. See text for details.

对于具有20个5m x 10m随机散射体的目标，从固定的大约54°视线角进行观察，则有效深度大约为10sin(54°) = 8.1 m。

A 20 scatterer, 5 m by 10 m random target was observed from a fixed aspectangle of about 54°, making its effective depth approximately 10sin(54°) = 8.1 m.

如果每个脉冲的工作频率都相同，那么目标RCS和接收到的回波功率应该完全相同。

If the same RFfrequency was used for each pulse, the RCS and thus received power would beexactly the same on each pulse.

然而，在上图中两个相邻脉冲的RF频率是按照18.5MHz步进的（根据式（2.63）计算），其起始频率为10.0GHz。

However, in this casethe RF frequency was increased by 18.5 MHz [calculated from Eq. (2.63)] fromone pulse to the next, starting at 10.0 GHz.

不同频率点之间的相对RCS波动约为38dB，线性值约为6300。

The resultingrelative RCS measurements vary by 38 dB, a factor of about 6300.

在第六章中可以看到，当连续的目标测量之间互不相关时，某些情况下的检测性能将会得到改善。

It will be seen inChap. 6 that in certain cases detection performance is improved when successivetarget measurements are uncorrelated.

因此，一些雷达采用频率捷变技术来实现连续测量数据之间的解相关(Ray, 1966)。

For this reason, someradars use a technique called frequency agility to force decorrelation ofsuccessive measurements (Ray, 1966).

在这一过程中，相邻脉冲之间的雷达频率以ΔF Hz或更高的频率递增，其中ΔF根据式（2.63）计算，从而确保相邻脉冲的目标回波之间的测量解相关。

In this process, theradar frequency is increased by ΔF Hz or more between successive pulses, whereΔF is given by Eq. (2.63), ensuring that the target echo decorrelates from onepulse to the next.

一旦获得期望的不相关测量次数，则下一组测量将循环使用设定好的频率增量周期。

Once the desirednumber of uncorrelated measurements is obtained, the cycle of increasingfrequencies is repeated for the next set of measurements.

式（2.63）是基于高度简化的目标模型以及相关间隔存在的假设前提。

Equation (2.63) isbased on a highly simplified target model and an assumption about whatconstitutes the correlation interval.

不同的相关间隔定义，例如通过相关函数首次下降到其峰值的1/2或1/e的点来定义，将导致对消除目标相关所需角度或频率变化的较小估计值。

A differentdefinition, for example defining the interval by the point at which thecorrelation function first drops to 1/2 or 1/e of its peak, would result in asmaller estimate of the required change in angle or frequency to decorrelatethe target.

此外，许多雷达是对回波幅度的平方进行处理的，而不是以上推导过程中假定的幅度值。

Also, many radars operateon the magnitude-squared of the echo amplitude, rather than the magnitude ashas been assumed in this derivation.

平方律检测器将产生与式（2.60）的平方成比例的相关函数（Birkmeier和Wallace，1963）。

A square law detectorproduces a correlation function proportional to the square of Eq.(2.60) (Birkmeier and Wallace, 1963).

因此第一零点的位置仍然是在相同的ΔK_θ值处，上述结论仍然是适用的。

The first zerotherefore occurs at the same value of ΔK_θ, and the previousconclusions still apply.

但是，如果使用了相关间隔的不同定义（例如以50%作为去相关点），则平方律检测所需的ΔK_θ变化将小于线性检测器所需的变化。

However, if adifferent definition of the correlation interval is used (such as the 50percent decorrelation point), the required change in ΔK_θ is less forthe square law than for the linear detector.

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

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