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Read the text and translate it: An antenna
⇐ ПредыдущаяСтр 5 из 5
An antenna is a transducer that transmits or receives electromagnetic waves. Antennas convert electromagnetic radiation into electric current, or vice versa. Antennas generally deal in the transmission and reception of radio waves, and are a necessary part of all radio equipment. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, cell phones, radar, and spacecraft communication. Antennas are most commonly employed in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.
An antenna is an arrangement of one or more conductors. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals. Some receiving antennas (parabolic, horn) incorporate shaped reflective surfaces to collect the radio waves striking them and direct or focus them onto the actual conductive elements.
Some of the first rudimentary antennas were built in 1888 by Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed the emitter dipole in the focal point of a parabolic reflector. The words antenna and aerial are used interchangeably; but usually a rigid metallic structure is termed an antenna and a wire format is called an aerial. A Hertzian antenna is a set of terminals that does not require the presence of a ground for its operation. A loaded antenna is an active antenna having an elongated portion of appreciable electrical length and having additional inductance or capacitance directly in series or shunt with the elongated portion so as to modify the standing wave pattern existing along the portion or to change the effective electrical length of the portion. An antenna grounding structure is a structure for establishing a reference potential level for operating the active antenna. It can be any structure closely associated with the ground which is connected to the terminal of the signal receiver or source opposing the active antenna terminal. There are two fundamental types of antenna directional patterns, which, with reference to a specific two dimensional plane (usually horizontal [parallel to the ground] or vertical [perpendicular to the ground]).
The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered on the resonant frequency. The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly and allowing the natural impedance to select the correct antenna. Small antennas are usually preferred for convenience, but there is a fundamental limit relating bandwidth, size and efficiency. The polarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally.
There are many variations of antennas.
The isotropic radiator is a purely theoretical antenna that radiates equally in all directions. It is considered to be a point in space with no dimensions and no mass.
The dipole antenna is simply two wires pointed in opposite directions arranged either horizontally or vertically, with one end of each wire connected to the radio and the other end hanging free in space.
The Yagi-Uda antenna is a directional variation of the dipole with parasitic elements added which are functionality similar to adding a reflector and lenses (directors) to focus a filament light bulb.
The random wire antenna is simply a very long wire with one end connected to the radio and the other in free space, arranged in any way most convenient for the space available.
The horn is used where high gain is needed, the wavelength is short (microwave) and space is not an issue. Horns can be narrow band or wide band, depending on their shape.
The parabolic antenna consists of an active element at the focus of a parabolic reflector to reflect the waves into a plane wave. Like the horn it is used for high gain, microwave applications, such as satellite dishes.
The patch antenna consists mainly of a square conductor mounted over a groundplane. Another example of a planar antenna is the tapered slot antenna (TSA), as the Vivaldi-antenna.
1. Put the words in the right order to make a sentence:
1. An, a, transducer, antenna, is, that, transmits, electromagnetic, or, receives, waves. 2. The, first, were, rudimentary, built, antennas, by, 1888, in, Heinrich Hertz 3. There, two, are, directional, fundamental, of, antenna, types, patterns. 4. A, a, the, Hertzian, not, antenna, presence, does, require, of, for, ground, its, operation. 5. Small, for, antennas, preferred, are, usually, convenience. 6. The, the, of, word, antenna, relative, is, to, to, wireless, apparatus, attributed, origin, Guglielmo Marconi.7. Antennas, its, are, any, radiotransmitter, in, order, electromagnetic, to, couple, electrical, connection, to, required, by, receiver, or, the, field.8. Resonant, be, resonant, expected, to, used, around, a, are, antennas, particular, frequency.9. Resonant, frequency, antenna, conductors, have, the, the, the, impedance, lowest, feedpoint, at.
2. Fill in the blanks with the following words:
the emitter, a transducer, wires, rod, conductor, transmission, an antenna, variations, types
1. An antenna is …that transmits or receives electromagnetic waves. 2. Hertz placed …dipole in the focal point of a parabolic reflector. 3. There are two fundamental …of antenna directional patterns 4. There are many …of antennas. 5. The bandwidth of …may be increased by several techniques. 6. The patch antenna consists mainly of a square … mounted over a groundplane. 7. The dipole antenna is simply two … pointed in opposite directions. 8. One example of antennas is the very common vertical antenna or whip antenna consisting of a metal …. 9. An antenna lead-in is the … line which connects the antenna to a transmitter or receiver.
3. Complete the following sentences using active vocabulary:
1. An antenna is a transducer that transmits or receives…2. Antennas are used in systems such as…3. Some of the first rudimentary antennas were built in 1888 …4. Small antennas are usually preferred for… 5. The bandwidth of an antenna may be increased by …6. The random wire antenna is simply a very long wire with… 7. The dipole antenna is simply two wires pointed in opposite directions arranged either… 8. A loaded antenna is an active antenna having an elongated portion of… 9. A Hertzian antenna is a set of terminals that does not require the presence of … 10. An antenna grounding structure is a structure for establishing …
4. Say if the following statements are true or false:
1. The first rudimentary antennas were built in 1888 by Clerk Maxwell. 2. An antenna is an arrangement only of more conductors. 3. There are three fundamental types of antenna directional patterns. 4. The bandwidth of an antenna may be decreased by several techniques. 5. A simple straight wire antenna will have a different polarization when mounted vertically, and one polarization when mounted horizontally.6. The parabolic antenna consists of a square conductor mounted over a groundplane. 7. The patch antenna consists mainly of an active element at the focus of a parabolic reflector to reflect the waves into a plane wave. 8. The isotropic radiator is a purely theoretical antenna that radiates only in one direction.
5. Answer the following questions:
1. What do antennas convert into electric current? 2. In what systems are antennas used? 3. How many fundamental types of antenna are there? 4. What is grounding structure of antenna? 5. How many variations of antennas are there? 6 Where is the horn used? 7. Where is the parabolic antenna used? 8. What is a bandwidth? 9. Does a Hertzian antenna require the presence of a ground for its operation?
6. Match the first part (1-7) of the sentence with the second part (a-g):
1. The isotropic radiator is
2. The dipole antenna is
3. The Yagi-Uda antenna is
4. The random wire antenna is
5. The horn is
6. The parabolic antenna
7. The patch antenna is
a) used where high gain is needed, the wavelength is short (microwave) and space is not an issue.
b) a radio frequency antenna consisting of a wire whose length does not bear a relation to the wavelength of the radio waves used, but is typically chosen more for convenience.
c) a popular antenna type, consists of a square conductor mounted over a groundplane.
d) a radio antenna that can be made by a simple wire, with a center-fed driven element.
e) a theoretical point source of waves which exhibits the same magnitude or properties when measured in all directions.
f) a directional antenna system consisting of an array of a dipole and additional closely coupled parasitic elements.
g) a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (radar).
7. Read the supplementary text, translate and entitle it:
A parabolic antenna is an antenna that uses a parabolic reflector, a surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it is highly directive; it functions analogously to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, that is they can produce the narrowest beam width angles, of any antenna type. They are used as high-gain antennas for point-to-point radio, television and data communications, and also for radiolocation (radar), on the UHF and microwave (SHF) parts of the radio spectrum. The relatively short wavelength of electromagnetic radiation at these frequencies allows reasonably sized reflectors to exhibit the desired highly directional response. With the advent of TVRO and DBS satellite television dishes, parabolic antennas have become a ubiquitous feature of the modern landscape. They are also widely used for terrestrial microwave relay links, ground based and airborne radar antennas, wireless WAN/LAN links, satellite and spacecraft communication antennas, and radio telescopes.
Render the text: An antenna
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