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Antennas act as transformers between conducted waves and electromagnetic waves propagating freely in space. Their name is borrowed from zoology, in which the Latin word “antennae” is used to describe the long, thin feelers possessed by many insects. The oldest existing antennas, such as those used by Heinrich Hertz in 1888 during his first experiments to prove the existence of electromagnetic waves, were in theory and in practice not so very different from an RF generator; in fact, resonant circuits are still frequently used even today as a means of explaining the individual properties of antennas. It was not until around 1900 or even later, when transmitting and receiving stations were being built, that a clear distinction was made and antennas were classified as separate components of radio systems.   At first glance, modern antennas look very much the same as their "ancient forebears"; however, as a rule they are optimized at great expense for their intended application. Communications technology strives first and foremost to transform one wave type into another with as little loss as possible. This requirement is less important in the case of test antennas, which are  intended to provide a precise measurement of the field strength at the installation site to a downstream test receiver; instead, their physical properties need to be known with high accuracy. The paper can describe only a few of the many forms of antenna that are in use today. The explanation of the physical parameters by which the behavior of each antenna can be both described and evaluated is probably of wider general use.

By Christof Rohner. Published July 2006.

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