The first two of these items concern antenna

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The first two of these items concern antenna performance. More than any other characteristic of a radar, its antenna determines the kinds of applications for which it will be useful. Chapters 2–4 of the text consequently discuss antennas in detail. Estimating the cross-section of a radar target requires some understanding of the physics of scattering. This topic is addressed in chapter 6. Noise in the environment and the radar equipment itself limit the ability to detect a scattered signal. Environmental and system noise will be discussed in chapter 5. For a target to be detected, the radar signal has to propagate from the radar to the target and back, and the manner in which it does so is affected by the intervening medium. Radio wave propagation in the Earth’s atmosphere and ionosphere is therefore explored in 9
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chapter 9. Perhaps most importantly, a considerable amount of data processing is usually required in order to extract meaningful information about the radar target from the received signal. Signal processing is therefore described in detail in chapters 8 and 9. The text concludes with the exploration of a few specialized radar applications in chapter 10. Fourier analysis and probability and statistics appear as recurring themes throughout the text. Both concepts are reviewed briefly later in this chapter. The review culminates with a definition of the power spectral density of a signal sampled from a random process. The Doppler spectrum is one of the most important outcomes of a radar experiment, and its meaning (and the meaning of the corresponding autocorrelation function) warrants special examination. 1.3 Conventions Like all disciplines, radar engineering is associated with specialized conventions, practices, and vernacular. Much of this concerns the language and the measures used to quantify antenna performance. In theory, there are any number of ways in which antennas could be characterized and evaluated. In practice, a system has developed over time for describing and comparing antennas on the basis of a few parameters. The system is highly intuitive and requires a minimum of computation. It can be applied in the absence of a detailed theoretical understanding of antennas and so will be described below. Another convention in widespread use, particularly among electrical engineers, is phasor notation. Phasor notation is not universal; physics textbooks often develop antenna theory without it, at the expense of somewhat more cluttered notation. Phasors simplify problems where they can be made to apply, but one must understand what’s going on to manipulate them properly. We therefore conclude this chapter with a review. 1.3.1 Antenna measures We begin with some basic, intuitive definitions. These will be refined as the text progresses. Here, the focus is on developing an intuitive understanding of how antennas are described and their performance quantified.
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