An antenna is a fundamental device used in electronic transmission systems that enables wireless communication. The main function of an antenna is to take an electrical signal and transmit it in a radio frequency, which propagates through the air. There are several different types of antennas. The two most common are monopole and dipole antennas, which originated from transmission line theory. A dipole is a half wavelength, open-ended transmission line that is fed at the midpoint of the antenna. A monopole is a quarter wavelength fed open-ended transmission line. Alternating current (AC) is fed into the dipole at a defined resonant frequency, which sends energy into the dipole for transmission. Because the transmission line is open ended all the energy is reflected, and as it reflects back a standing wave of energy is created. This causes the dipole to radiate its energy orthogonal to the direction of the current. Dipoles and monopoles are used today for radio transmission and cell tower broadcasting. Printed circuit board antennas, known as patch antennas or planar inverted-F antennas (PIFA) are another type of antenna commonly used in portable devices due to their small form factor. 더 읽기 읽기 안 함