Antennas

Antennas, as essential parts of a radio system, are defined as the devices that can radiate and receive electromagnetic energy in an efficient and desired manner. There are many different types of antennas, most of them designed specifically to fit a definite application. Although some of them, which were introduced many decades before, are still in use, there are also new antenna systems that follow modern demands for greater performance of various radio systems. The area of antennas is characterized as vigorous and dynamic. A suitable approach is the classification of antennas generally into the following categories: wire antennas, reflector antennas, lens antennas, traveling wave antennas, frequency‐independent antennas, horn antennas, and conformal antennas. Antenna arrays, formed by suitably spacing radiating elements, are used to improve the characteristics of an individual antenna element. Reconfigurable antennas can radiate at different frequencies and polarizations and more than one pattern, providing more functionality in modern systems. Antennas enjoy a very large range of applications, both in the military and in the commercial world. The most well‐known applications of antennas are associated with radio, TV, and communication systems. Today, antennas find extensive use in biomedicine, radar, remote sensing, astronomy, navigation, radio frequency identification, controlling space vehicles, collision avoidance, air traffic control, GPS, pagers, wireless telephone, wireless local area networks, and so on.