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Antenna Theory and Applications by Hubregt J. Visser

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Chapter 2

Antenna System-Level Performance Parameters

Now that we have developed a basic understanding of the operation of antennas, based on physical reasoning, it is time to quantify and interrelate the different antenna parameters that describe antenna functioning. Therefore, in this chapter we will introduce these system-level performance parameters for antennas.1 With these parameters we will be able to calculate the effect of an antenna or antennas in a communication or radar system.

2.1 Radiation Pattern

In the previous chapter we saw that accelerating charge—and thus displacement of charge—is the cause of electromagnetic radiation. Due to this displacement, every antenna must have a non-zero size. We have already seen that even the smallest-size antenna produces an electromagnetic radiation (propagating field disturbance) that is not uniform (i.e. not equally distributed in all directions), see Figures 1.41.6. This non-uniform radiation is described by the so-called radiation pattern, which is evaluated in the far-field.

Although uniformly radiating antennas or isotropic radiators cannot exist in real life, they may come in handy for comparing different antennas. The uniform radiator must then be seen as a mathematical abstraction.

2.1.1 Field Regions

When talking about radiated fields, we have to take into account the distance relative to the antenna where these fields are evaluated. Close to the antenna, a region exists where energy is stored and returned to the antenna. ...

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