Basic Overview Of Military Antennas
The antennas are characterized by a number of parameters. Radiation pattern is a graphic representation of radiation characteristics of an antenna according to direction (azimuth and elevation coordinates). Most often represent the radiated power density, but also can find diagrams or phase bias (military antennas). Considering the radiative pattern, we can make a general classification of types of antenna and we can define the directivity of a receiver (isotropic antenna, directional, bi-directional, omni).
Most radio aerials today is primarily designed to be able to send or receive radio waves in a narrow frequency band, for example. FM via VHF band II (87.5-108 MHz). Masts propagate / receives radio waves through coupling with the alternating magnetic field. These types of antenna are used for long-wave, medium-wave and short-wave up to about 6MHz. It is possible to realize antennas that operate according to this principle, up to 60 MHz.
A typical loop antenna is made of copper, in resonance with a variable capacitor when transmitting and can withstand high voltages. The transmission can take many amps and the voltage across the capacitor several kilovolts. Loops of copper are more effective than lower managers, due to the large flow. Loops are circular and more efficient than squares, an alternative is octagoner that are easier to manufacture.
Comparing an antenna yagi with a satellite, the antenna yagi have a F / B ratio of about 15 dB (depending on model and manufacturer) while for the parabolic relationship F / B is> 35dB (depending on model and manufacturer) . This is observed as "good" antenna on rejection of signals by the rear. The higher the paramentro in parabolic antennas will be better. The 15 dB of antenna yagui it can also be interpreted as the attenuation that would have on the system, if for example a bounced capture of a building, by the rear of the wave. Radiation resistance - when power is supplied to an aerial, radiating part of it and part is converted into heat dissipating. When talking about radiation resistance, it is made taking into account that cannot be measured directly.
A transmitter with more than about 3 items are usually less sensitive in a circle slice perpendicular towards the main direction of a jet and therefore one can put antennas in close proximity to a base station. The distance between the antennas should be at least 1 / 2-1 of main wavelengths used. Further away than about 10 wavelengths (far field) affects largely the antenna radiation pattern, but it can affect radio propagation or radio broadcast.
You can also define the beam width between zero, which is the angular range of the main beam of a radiation pattern between two adjacent zeros to maximum. Create antennas radiated electromagnetic fields. Polarized electromagnetic defined in a certain direction, as the geometric shape that traces the edge of electric field vector at a certain distance from the antenna, to change the time.
The polarization can be linear, circular and elliptical. Linear polarization can take different orientations (horizontal, vertical, +45, -45). The circular or elliptical polarizations can be right or left (right-handed or left-handed), according to the direction of rotation of the field (observed away from the antenna). Transmitters within decoupling coefficient defined polarization. This measures the amount of power that is capable of receiving a polarized antenna of a form having an effective.
The characteristics of an antenna depends on the relationship between the dimensions and the wavelength of a signal transmitted or received radio frequency. If the masts dimensions are much smaller than the wavelength are called elementary antennas, whether they have dimensions of order of a half wavelength resonating and if its size is much larger than the wavelength are directives.
Most radio aerials today is primarily designed to be able to send or receive radio waves in a narrow frequency band, for example. FM via VHF band II (87.5-108 MHz). Masts propagate / receives radio waves through coupling with the alternating magnetic field. These types of antenna are used for long-wave, medium-wave and short-wave up to about 6MHz. It is possible to realize antennas that operate according to this principle, up to 60 MHz.
A typical loop antenna is made of copper, in resonance with a variable capacitor when transmitting and can withstand high voltages. The transmission can take many amps and the voltage across the capacitor several kilovolts. Loops of copper are more effective than lower managers, due to the large flow. Loops are circular and more efficient than squares, an alternative is octagoner that are easier to manufacture.
Comparing an antenna yagi with a satellite, the antenna yagi have a F / B ratio of about 15 dB (depending on model and manufacturer) while for the parabolic relationship F / B is> 35dB (depending on model and manufacturer) . This is observed as "good" antenna on rejection of signals by the rear. The higher the paramentro in parabolic antennas will be better. The 15 dB of antenna yagui it can also be interpreted as the attenuation that would have on the system, if for example a bounced capture of a building, by the rear of the wave. Radiation resistance - when power is supplied to an aerial, radiating part of it and part is converted into heat dissipating. When talking about radiation resistance, it is made taking into account that cannot be measured directly.
A transmitter with more than about 3 items are usually less sensitive in a circle slice perpendicular towards the main direction of a jet and therefore one can put antennas in close proximity to a base station. The distance between the antennas should be at least 1 / 2-1 of main wavelengths used. Further away than about 10 wavelengths (far field) affects largely the antenna radiation pattern, but it can affect radio propagation or radio broadcast.
You can also define the beam width between zero, which is the angular range of the main beam of a radiation pattern between two adjacent zeros to maximum. Create antennas radiated electromagnetic fields. Polarized electromagnetic defined in a certain direction, as the geometric shape that traces the edge of electric field vector at a certain distance from the antenna, to change the time.
The polarization can be linear, circular and elliptical. Linear polarization can take different orientations (horizontal, vertical, +45, -45). The circular or elliptical polarizations can be right or left (right-handed or left-handed), according to the direction of rotation of the field (observed away from the antenna). Transmitters within decoupling coefficient defined polarization. This measures the amount of power that is capable of receiving a polarized antenna of a form having an effective.
The characteristics of an antenna depends on the relationship between the dimensions and the wavelength of a signal transmitted or received radio frequency. If the masts dimensions are much smaller than the wavelength are called elementary antennas, whether they have dimensions of order of a half wavelength resonating and if its size is much larger than the wavelength are directives.
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