Antenna An antenna is a specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) or vice-versa. There are two basic types: the receiving antenna, which intercepts RF energy and delivers AC to electronic equipment, and the transmitting antenna, which is fed with AC from electronic equipment and generates an RF field.
[1.Antennas: isotropic radiator Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission
a. Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna b. Real antennas always have directive effects (vertically and/or horizontally) c. Radiation pattern: measurement of radiation around an antenna]
2 Simplest Real Antennas
![Hertz Antenna a. dipole antenna, with ½ wavelength
b. very small, compared to its wavelength that is about one-hundredths of the wavelength at its operating frequency
c. radiation pattern of hertz antenna is not truly isotropic
d. Normally used for small applications and was used in set top TV antennas.]
![Marconi Antenna a. vertical wire with a length of 1/4 of the working wavelength
b. length of the wire in meters is calculated as L = ( 71,25 / Frequency MHz)
a. used in the radio broadcasting transmitters of high power ]
![3 Directional Antenna a. Have a certain preferential direction of transmission and reception.
b. It can be some special satellite dishes.
c. A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing for increased performance and reduced interference from unwanted sources.
d. Used for microwave connection or base station for mobile phone.]
![4 Sector Antenna a. A sector antenna is a type of directional microwave antenna with a sector-shaped radiation pattern.
b. The largest use of these antennas is as antennas for cell phone base-station sites. They are also used for other types of mobile communications, for example in WiFi networks. They are used for limited-range distances of around 4 to 5 km.
c. Consist of several directed antennas combined on a single pole.
d. Allow for frequency reuse in cell by splitting the cell in to 3 and 6 sector.]