Contents 1 Terminology 2 Overview 3 Parameters 3.1 Resonant frequency 3.2 Gain 3.3 Radiation pattern 3.4 Impedance 3.5 Efficiency 3.6 Bandwidth 3.7 Polarization 3.8 Transmission and reception 4 Basic antenna models 5 www.08.coolagin.ru Practical antennas

Antenna (radio)

From Wikipedia, the free encyclopedia

An antenna is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, radar, and space exploration. Antennas usually work in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.

Physically, an antenna is an arrangement of conductors that generate a radiating electromagnetic field in response to an applied alternating voltage and the associated alternating electric current, or can be placed in an electromagnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. Some antenna devices (parabolic antenna, Horn Antenna) just adapt the free space to another type of antenna.

Thomas Edison used antennas by 1885. Edison patented his system in U.S. Patent 465,971 . Antennas were also used in 1888 by Heinrich Hertz (1857-1894) 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. He published his work and installation drawings in Annalen der Physik und Chemie (vol. 36, 1889).

Terminology

The words antenna (plural: antennas^[1]) and "aerial" are used interchangeably; but usually a rigid metallic structure is termed an antenna and a wire format is called an aerial. In the United Kingdom and other British English speaking areas the term aerial is more common, even for rigid types. The noun aerial is occasionally written with a diaresis mark — aërial — in recognition of the original spelling of the adjective aërial from which the noun is derived.

The origin of the word antenna relative to wireless apparatus is attributed to Guglielmo Marconi. In 1895, while testing early radio apparatus in the Swiss Alps at Salvan, Switzerland in the Mont Blanc region, Marconi experimented with early wireless equipment. A 2.5 meter long pole, along which was carried a wire, was used as a radiating and receiving aerial element. In Italian a tent pole is known as l'antenna centrale, and the pole with a wire alongside it used as an aerial was simply called l'antenna. Until then wireless radiating transmitting and receiving elements were known simply as aerials or terminals. Marconi's use of the word antenna (Italian for pole) would become a popular term for what today is uniformly known as the antenna.^[2] .

A Hertzian antenna is a set of terminals that does not require the presence of a ground for its operation (versus a Tesla antenna which is grounded. ^[3]) 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 (or acting as) the ground which is connected to the terminal of the signal receiver or source opposing the active antenna terminal, (i.e., the signal receiver or source is interposed between the active antenna and this structure).

Overview

Antennas have practical uses for the transmission and reception of radio frequency signals (radio, TV, etc.). In air, those signals travel close to the speed of light in vacuum and with a very low transmission loss. The signals are absorbed when propagating through more conducting materials, such as concrete walls, rock, etc. When encountering an interface, the waves are partially reflected and partially transmitted through.

The vast majority of antennas are simple vertical rods a quarter of a wavelength long. Such antennas are simple in construction, usually inexpensive, and both radiate in and receive from all horizontal directions (omnidirectional). One limitation of this antenna is that it does not radiate or receive in the direction in which the rod points. This region is called the antenna blind cone or null.

There are two fundamental types of antennas, which, with reference to a specific three dimensional (usually horizontal or vertical) plane are either:

1. Omni-directional (radiates equally in all directions), such as a vertical rod or

2. Directional (radiates more in one direction than in the other).

In colloquial usage omni-directional usually refers to all horizontal directions with reception above and below the antenna being reduced in favor of better reception (and thus range) in other directions. Also directional antennas are usually meant to refer to one targeting a single specific direction such as a telescope, satellite dish, or possibly a 120° horizontal reception and transmission area.

All antennas radiate some energy in all directions in free space but careful construction results in substantial transmission of energy in a preferred direction and negligible energy radiated in other directions.

By adding additional conducting rods or coils (called elements) and varying their length, spacing, and orientation (or changing the direction of the antenna beam), an antenna with specific desired properties can be created, such as a Yagi-Uda Antenna (often abbreviated to "Yagi").

An antenna array is two or more antennas coupled to a common source or load to produce a specific directional radiation pattern. The spatial relationship between individual antennas contributes to the directivity of the antenna.

The term active element is intended to describe an element whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input.

An antenna lead-in is the medium, for example, a transmission line or feed line for conveying the signal energy between the signal source or receiver and the antenna. The antenna feed refers to the components between the antenna and an amplifier.

An antenna counterpoise is a structure of conductive material most closely associated with ground that may be insulated from or capacitively coupled to the natural ground. It aids in the function of the natural ground, particularly where variations (or limitations) of the characteristics of the natural ground interfere with its proper function. Such structures are usually connected to the terminal of a receiver or source opposite to the antenna terminal.

An antenna component is a portion of the antenna performing a distinct function and limited for use in an antenna, as for example, a reflector, director, or active antenna.

Parasitic elements are usually metallic conductive structures which reradiate into free space impinging electromagnetic radiation coming from or going to the active antenna.

An electromagnetic wave refractor is a structure which is shaped or positioned to delay or accelerate transmitted electromagnetic waves, passing through such structure, an amount which varies over the wave front. The refractor alters the direction of propagation of the waves emitted from the structure with respect to the waves impinging on the structure. It can alternatively bring the wave to a focus or alter the wave front in other ways, such as to convert a spherical wave front to a planar wave front (or vice versa). The velocity of the waves radiated have a component which is in the same direction (director) or in the opposite direction (reflector) that of the velocity of the impinging wave.

A director is usually a metallic conductive structure which reradiates into free space impinging electromagnetic radiation coming from or going to the active antenna, the velocity of the reradiated wave having a component in the direction of velocity of the impinging wave. The director modifies the radiation pattern of the active antenna and there is no significant potential relationship between the active antenna and this conductive structure.

A reflector is usually a metallic conductive structure (e.g., screen, rod or plate) which reradiates back into free space impinging electromagnetic radiation coming from or going to the active antenna. The velocity of the returned wave having a component in a direction opposite to the direction of velocity of the impinging wave. The reflector modifies the radiation of the active antenna. There is no significant potential relationship between the active antenna and this conductive structure.

An antenna coupling network is a passive network (which may be any combination of a resistive, inductive or capacitive circuit(s)) for transmitting the signal energy between the active antenna and a source (or receiver) of such signal energy.

Typically, antennas are designed to operate in a relatively narrow frequency range. The design criteria for receiving and transmitting antennas differ slightly, but generally an antenna can receive and transmit equally well. This property is called reciprocity.

Антенна (радио)

От Wikipedia, свободной энциклопедии

Антенна - преобразователь, разработанный, чтобы передать или получить электромагнитные волны. Другими словами, антенны преобразовывают электромагнитные волны в электрические потоки и наоборот. Антенны используются в системах, таких как радио и радиовещание телевидения, двухточечная радио-коммуникация, беспроводная ЛВС, радар, и исследование космоса. Антенны обычно работают в воздухе или космосе, но могут также управляться под водой или даже через почву и скалу в определенных частотах для коротких расстояний.

Физически, антенна - договоренность проводников, которые производят исходящую электромагнитную область в ответ на прикладное переменное напряжение и связанный переменный электрический ток, или могут быть помещены в электромагнитную область так, чтобы область вызвала переменный ток в антенне и напряжении между его терминалами. Некоторые устройства антенны (параболическая антенна, Роговая Антенна) только приспосабливают свободное место к другому типу антенны.

К 1885 Томас Edison использовал антенны. Edison запатентовал свою систему в американских Доступных 465 971. Антенны также использовались в 1888 Heinrich Hertz (1857-1894), чтобы доказать существование электромагнитных волн, предсказанных в соответствии с теорией Джеймса Clerk Maxwell. Герц поместил диполь эмитента в фокус параболического отражателя. Он издал свою работу и инсталляционные рисунки в Annalen der Physik und Chemie (издание 36, 1889).

Терминология

Антенна слов (множественное число: антенны ^[1]), и "антенна" используются попеременно; но обычно твердую металлическую структуру называют антенной, и проводной формат называют антенной. В Великобритании и другой британский вариант английского языка, говоря области термин антенна больше характерен, даже для твердых типов. Антенна существительного иногда пишется с маркой diaresis - aërial - с учетом оригинального правописания прилагательного aërial, из которого получено существительное.

Происхождение антенны слова относительно беспроводного аппарата приписано Guglielmo Marconi. В 1895, проверяя ранний радио-аппарат в швейцарских Альпах в Salvan, Швейцария в Монбланской области, Marconi экспериментировал с ранним беспроводным оборудованием. Полюс 2.5 метра длиной, вдоль которого несся провод, использовался как излучение и получение воздушного элемента. На итальянском языке столб для палатки известен как l'antenna centrale, и полюс с проводом рядом с используемым, поскольку антенну просто назвали l'antenna. До тех пор излучение радио передавшие и получающие элементы было известно просто как антенны или терминалы. Использование Marconi's антенны слова (итальянский язык для полюса) стало бы популярным сроком для того, что сегодня однородно известно как антенна. ^[2].