An antenna (or aerial) is a transducer that transmits or receives electromagnetic waves. In other words, antennas convert electromagnetic radiation into electrical 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.
Physically, an antenna is an arrangement of one or more conductors, usually called elements in this context. 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 (such as parabolic and horn types) 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 (1857-1894) 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. He published his work and installation drawings in Annalen der Physik und Chemie
The words antenna (plural: antennas 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 diaeresis 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 apparatuses 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.
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). 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.
In colloquial usage, the word antenna may refer broadly to an entire assembly including support structure, enclosure (if any), etc. in addition to the purely functional components.
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* Brief overview to the area of Systems theory.
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Systems theory is a set of theoretical concepts used to describe a wide variety of thing in terms of a model called a system. To give it context lets talk a bit about it’s origins.
Of cause people have been coming up with abstract theories about how the world work for a long time. Some ancient Greeks thought everything was made of earth, water, fire and air, whilst others came to the conclusion that it was the expression of perfect geometric forms.
Over the years our theoretical systems have grown into large and sophisticated bodies of knowledge such as philosophy, mathematics and the many areas of theoretical science, although these theoretical frameworks are often limited to relatively specific area of interest.
During the 20th century Systems theory emerged as a new theory that draws upon many core concepts within these pre-existing methods to develop a more abstract framework that is design to be universally applicable to all domains.
In order to achieve such a general relevance, system theory starts with the abstract concept of a system and then applies this to modeling various different phenomena from biological to social and technical systems.
The model of a system can be loosely defined as a set of parts often called elements that form a whole, which is referred to as the system. A system exists within an environment and has a boundary that differentiated the systems exterior from its interior.
An example of this might be a country, interior to which are all the people, institution and other elements that constitutes the nation as an entire system. Whilst exterior to its boundary is the international political environment.
A system can be either open or isolated, isolated systems do not interact with their environment, but most systems are open meaning there is an exchange of energy and resources between the system and its environment.
The passing of energy or resources from the exterior of the systems boundary to the interior is termed an input whilst the reverse is termed an output.
Systems develop or function through the input of energy or resources from their environment, they process this energy by transforming it to create an output, if this output is of some value to its environment it can be termed energy.
If on the other hand it is of negative value it may be termed entropy, a scientific term for lack of order, disarrangement or in more familiar terms we might call it waste.
An early use of this type of model was during the development of the steam-engine where scientist and engineers were thinking about the amount of fuel inputted to the engine relative to the power out put and heat energy wasted. By using this model they could create a quantifiable ration between them that we would now term the efficiency of the system.
Of cause this same reasoning can be applied to a wide variety of phenomena from the processing of energy within a plant cell to the efficiency of a business organization.
We can model systems on various scales, thus elements can form part of systems that themselves form part of larger systems and so on, this is termed nesting or encapsulation and helps us to analyst a system on various levels whilst hiding away the underlining complexity.
Systems theory explores many other areas such as Emergence that raises key question about the relationship between the parts within a system and the hole, that is how elements can function together or self organize to create some new and emergent structure as an entirety…
Complexity Science: 4 Systems Theory