Working Principle and History
– Antenna is the interface between radio waves and electric currents
– Transmitter supplies electric current to antenna terminals
– Antenna radiates energy from current as electromagnetic waves
– Receiver intercepts power of radio wave to produce electric current
– Antennas were first built in 1888 by Heinrich Hertz
– Guglielmo Marconi developed practical antennas for wireless telegraphy
– Marconi’s use of the word ‘antenna’ spread among researchers and the public
– Antennas were used to prove the existence of electromagnetic waves
– Antennas have evolved to include reflectors, horns, and parasitic elements
Terminology and Overview
– ‘Antenna’ and ‘aerial’ are used interchangeably
– ‘Aerial’ can refer specifically to an elevated horizontal wire antenna
– The word ‘antenna’ originated from Marconi’s use of ‘lantenna’
– ‘Antenna’ can refer to the entire assembly including support structure
– Receiving antennas may include integrated preamplifiers or mixers
– Antennas are required for radio receivers and transmitters
– Radio waves carry signals through the air with almost no transmission loss
– Antennas can be omnidirectional or directional
– Beam antennas are designed for maximum response in a specific direction
– Dipole antennas can be combined into arrays for increased directionality
Antenna Characteristics
– Dipole antennas are balanced components with equal but opposite voltages
– Monopole antennas rely on a conductive surface, such as the ground
– Additional elements in the antenna structure increase directionality
– Antenna gain describes the concentration of radiated power
– Phased arrays combine multiple antennas for directional control
Types of Antennas
– Log-periodic dipole array: connected dipole elements with progressive lengths in an endfire array for directional reception
– Yagi-Uda antenna: one dipole element with parasitic elements for highly directional reception with narrow bandwidth
– Aperture antennas: parabolic reflector or horn antenna for increased directionality, more practical at higher frequencies
– Vertical towers: used for low-frequency directionality in arrays for large land occupation
– Beverage antenna: long antenna with significant directivity for reception
Antenna Feed and Lead-in, Counterpoise and Refractor, Reciprocity
– Antenna feed: components connecting the antenna to the transmitter or receiver, including impedance matching network and transmission line
– Aperture antenna feed: basic radiating antenna embedded in the entire system of reflecting elements
– Microwave antenna feed: direct connection from waveguide instead of a transmission line
– Antenna lead-in: transmission line connecting the antenna to a transmitter or receiver
– Coupling network: passive network for impedance matching between the antenna and the transmitter or receiver
– Antenna counterpoise: conductive structure improving or substituting for the ground in monopole antennas
– Electromagnetic wave refractor: component selectively delaying or advancing portions of the wavefront passing through it to maximize directivity
– Ground plane: structure connected to the return connection of an unbalanced transmission line, aiding in the function of the natural ground
– Refractor in aperture antennas: alters spatial characteristics of the wave to focus or alter the wavefront for increased directivity
– Radio equivalent of optical lens: refractor in antenna systems
– Electrical characteristics of an antenna are the same whether it is transmitting or receiving
– Receiving pattern of an antenna is identical to its radiation pattern when driven as a radiator
– Reciprocity theorem of electromagnetics ensures no distinction between receiving and transmitting terminology
– Linear and reciprocal materials in the antenna and transmission medium are necessary for reciprocity
– Some microwave antennas use nonreciprocal materials for different behavior on receiving than transmitting Source: https://en.wikipedia.org/wiki/Antenna_(radio)
In radio engineering, an antenna (American English) or aerial (British English) is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.
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| Working principle | Electromagnetic radiation |
|---|---|
| Invented | Heinrich Hertz |
| First production | 1886 |
| Electronic symbol | |
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An antenna is an array of conductors (elements), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional, or high-gain, or "beam" antennas). An antenna may include components not connected to the transmitter, parabolic reflectors, horns, or parasitic elements, which serve to direct the radio waves into a beam or other desired radiation pattern. Strong directivity and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than a half wavelength.
The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of waves predicted by the electromagnetic theory of James Clerk Maxwell. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received a Nobel Prize.
