The antenna plays an essential role in sending and receiving information in the wireless communication systems. In addition to communication systems antennas are used in astronomy, geophysical probing, medicine and biological tissues, and radio frequency identification systems. Based on their geometrical structure, antennas may be classified into wire antennas; aperture type antennas; microstrip antennas; array antennas; reflector antennas; lens antennas. This chapter introduces the basic principles of antennas beside some topics related to antennas such as reciprocity theorem, Friis transmission formula, and general formulations for far-field approximations. As examples of the antenna analysis, the basic antenna parameters, and radiation characteristics are obtained for wire antennas and simple array antennas. The topics of the chapter are analyzed in details and supported by illustrative examples and figures in addition to solved problems. Homework problems are included at the end of the chapter.
Keywords: Aperture type antennas, array antennas, circular loop antenna, directivity, dipole antenna, effective aperture, Friis transmission formula, farfield, gain, input impedance, lens antennas, microstrip antennas, radiation pattern, radiating near-field region, reactive near-field region, reciprocity theorem, reflector antennas, wire antennas.