The Functions of Radio Antennas
44336
Arts & Entertainment
Jul 31, 2007
Tymon Hytem
The Functions of Radio Antennas
Radio antennas have two fold functions. First of these functions is to radiate the radio frequency energy generated in the transmitter and fed to the antenna by a transmission line. In this capacity the antenna acts as the impedance matching device to match the impedance of the transmission line to that of free space. The other function of the antenna is to direct the energy into desired direction and to suppress the radiations in unwanted directions
A completely non directional or omni directional radiator radiates uniformly in all directions and is known as isotropic radiators. A point source of sound is an example of isotropic radiator in acoustics. There are no such things as an isotropic radiator of electromagnetic energy since all radio antennas have some directivity. However the notion of a completely non directional source is useful especially for gain comparison purposes.
The radiation pattern of an antenna is a graphical representation of the radiation of the antenna as a function of direction. When the radiation is expressed as field strength volt per meter the radiation pattern is a field strength pattern. If the radiation in a given direction is expressed in terms of power per unit solid angle the resulting pattern is a power pattern. A power pattern is proportional to the square of the field strength pattern. The co ordinate system generally used in the specification of antenna radiation pattern is the spherical co ordinate system. The antenna is locked near the origin of the system and the field strength is specified at points on the spherical surface of radius. The shape of radiation pattern is independent of radius as long as radius is chosen sufficiently large. When this is true the magnitude of the field strength in any direction varies inversely with radius and so needs to be stated for one value of radius. For example in broadcast antenna work it is customary to state the field strength at a radius of one mile or one kilo meter. Often only the relative radiation pattern is used. This gives the relative field strength in various directions. Usually it is referred to unity in the direction of maximum radiation.
Antenna represents circuits with distributed constants but for the sake of analysis we can show the lumped inductance and lumped capacitance of an antenna system in the form of an oscillatory circuit. The circuit consists of a condenser whose plates are connected by a vertical wire which contains a certain amount of a self inductance. A radio frequency voltage is included at the center of the circuit. The frequency of the source usually corresponds to the resonant frequency of the circuit. This arrangement is often referred to as a dipole.
Tymon Hytem has worked in the electronics feild for the past 15 years. He enjoys helping people decide on electronic gadgets from telephones to XM Radio and choosing the perfect XM Satellite Radio system for their needs. send email to Tymon Hytem
A completely non directional or omni directional radiator radiates uniformly in all directions and is known as isotropic radiators. A point source of sound is an example of isotropic radiator in acoustics. There are no such things as an isotropic radiator of electromagnetic energy since all radio antennas have some directivity. However the notion of a completely non directional source is useful especially for gain comparison purposes.
The radiation pattern of an antenna is a graphical representation of the radiation of the antenna as a function of direction. When the radiation is expressed as field strength volt per meter the radiation pattern is a field strength pattern. If the radiation in a given direction is expressed in terms of power per unit solid angle the resulting pattern is a power pattern. A power pattern is proportional to the square of the field strength pattern. The co ordinate system generally used in the specification of antenna radiation pattern is the spherical co ordinate system. The antenna is locked near the origin of the system and the field strength is specified at points on the spherical surface of radius. The shape of radiation pattern is independent of radius as long as radius is chosen sufficiently large. When this is true the magnitude of the field strength in any direction varies inversely with radius and so needs to be stated for one value of radius. For example in broadcast antenna work it is customary to state the field strength at a radius of one mile or one kilo meter. Often only the relative radiation pattern is used. This gives the relative field strength in various directions. Usually it is referred to unity in the direction of maximum radiation.
Antenna represents circuits with distributed constants but for the sake of analysis we can show the lumped inductance and lumped capacitance of an antenna system in the form of an oscillatory circuit. The circuit consists of a condenser whose plates are connected by a vertical wire which contains a certain amount of a self inductance. A radio frequency voltage is included at the center of the circuit. The frequency of the source usually corresponds to the resonant frequency of the circuit. This arrangement is often referred to as a dipole.
Tymon Hytem has worked in the electronics feild for the past 15 years. He enjoys helping people decide on electronic gadgets from telephones to XM Radio and choosing the perfect XM Satellite Radio system for their needs. send email to Tymon Hytem
Write a Review
Add to My Favorite
Refer it to Friend
Report Article
Other links at Arts & Entertainment
The amplitude radio transmitter using high frequency power level of carrier has the following constituent stages namely master oscillator, buffer amplifier or isolating amplifier, harmonic generators, class C power amplifiers, modulated amplifier and the
Category:
Native American drums are one of the most recognizable Native American instruments. Drums for generations have been at the center of Native lifestyle, forming what has become the foundation the history of Native Americans.
Category:
JAG minas k?nnanden f?rr?da och olycklig. Jag var bara fjorton , och Ifall tok avslutande examen fr?n h?g skolen i en annan m?nad. Han har redan undertecknat upp till f?rena den ?rlogsflotta. Han var lik en gammalt bror , och han skulle har hatt b?ttre si
Category:
For hundreds of years, what is now the Detroit area was so important to commerce between Native American tribes that only traders were allowed into the territory.
Category:
When the transmitting and the receiving antennas are close to the surface of the earth, the space is negligibly small and the surface wave alone is of importance, thus the day time propagation of the broadcast signals takes place only through surface wave
Category:
Site Sponsor
Directory Statistics
Articles: 68214
Categories: 501
Yahoo Entertainment
