相邻脉冲之间的间隔称为脉冲重复间隔（PRI），PRI的倒数是脉冲重复频率（PRF）。
The interval between pulses is called thepulse repetition interval (PRI), and its inverse is the pulse repetitionfrequency (PRF).
PRF的变化范围很大，但通常在每秒几百个脉冲（pps）到每秒几万个脉冲之间。
PRF varies widely but is typically betweenseveral hundred pulses per second (pps) and several tens of thousands of pulsesper second.
脉冲雷达系统的占空比通常相对较低，通常远低于1％（感觉应该是10%比较合适，如果对于远程预警雷达来说，这句话应该比较合适！！！），因此平均功率很少超过10至20千瓦。
The duty cycle of pulsed systems is usuallyrelatively low and often well below 1 percent, so that average powers rarelyexceed 10 to 20 kW.
COBRA DANE再次提供了一个极端的例子，其平均功率为0.92兆瓦。
COBRA DANE again offers an extreme examplewith its average power of 0.92 MW.
雷达发射脉冲长度通常介于100ns到100μs之间，甚至一些系统使用短至几纳秒的脉冲，而某些系统使用非常长的脉冲，大约在1ms量级。
Pulse lengths are most often between about100 ns and 100 μs, though some systems use pulses as short as a few nanosecondswhile others have extremely long pulses, on the order of 1 ms.
从本书第六章可以看到，雷达所能达到的检测性能随着发射波形能量的增加而提高。
It will be seen (Chap. 6) that the detectionperformance achievable by a radar improves with the amount of energy in thetransmitted waveform.
为了使得雷达的探测距离最大化，大多数的雷达系统会尽量增大发射功率。
To maximize detection range, most radarsystems try to maximize the transmitted power.
其中一种方法是在脉冲发射期间始终以全功率进行辐射。
One way to do this is to always operate thetransmitter at full power during a pulse.
因此，雷达通常不会使用发送脉冲的幅度调制。（因为幅度调制产生的波动会损失发射信号的能量！！！）
Thus, radars generally do not use amplitudemodulation of the transmitted pulse.
另一方面，根据第四章的讲解，标称距离分辨率ΔR由波形带宽β决定。
On the other hand, the nominal rangeresolution ΔR is determined by the waveform bandwidth β according to Chap. 4.
对于未调制的脉冲，带宽与其持续时间成反比。
For an unmodulated pulse, the bandwidth isinversely proportional to its duration.
为了增大固定脉冲长度的波形带宽，而不会牺牲能量，许多雷达通常使用脉冲的相位或频率调制。
To increase waveform bandwidth for a givenpulse length without sacrificing energy, many radars routinely use phase orfrequency modulation of the pulse.
理想的距离分辨率从远程监视雷达系统（倾向于较低RF）的几公里变化到非常精细的成像系统（倾向于较高RF）中的一米或更小。
Desirable values of range resolution varyfrom a few kilometers in long-range surveillance systems, which tend to operateat lower RFs, to a meter or less in very fine-resolution imaging systems, whichtend to operate at high RFs.
相应的波形带宽在100kHz到1GHz的量级，带宽通常为RF的1%或更小。
Corresponding waveform bandwidths are onthe order of 100 kHz to 1 GHz, and are typically 1 percent or less of the RF.
几乎没有雷达的带宽会达到射频的10%。
Few radars achieve 10 percent bandwidth.
因此，大多数雷达波形可以被认为是窄带的带通信号。
Thus, most radar waveforms can be considerednarrowband, bandpass functions.
1.3.2天线
1.3.2. Antennas
天线是决定雷达灵敏度和角分辨率的主要因素。
The antenna plays a major role indetermining the sensitivity and angular resolution of the radar.
雷达系统中可能会使用多种天线类型。
A wide variety of antenna types are used inradar systems.
一些常见的天线类型是抛物面反射天线、扫描馈电天线、透镜天线和相控阵天线。
Some of the more common types are parabolicreflector antennas, scanning feed antennas, lens antennas, and phased arrayantennas.
从信号处理的角度来看，天线最重要的特性是增益、波束宽度和副瓣电平。
From a signal processing perspective, themost important properties of an antenna are its gain, beamwidth, and sidelobelevels.
这些指标都是从天线功率方向图出发考虑的。
Each of these follows from consideration ofthe antenna power pattern.
天线功率方向图P(θ, ϕ)描述了相对天线视轴(θ, ϕ)方向上的辐射强度。
The power pattern P(θ, ϕ) describes the radiationintensity during transmission in the direction (θ, ϕ) relative to the antennaboresight.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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