Caracteristicas de las antenas

Caracteristicas de una antena

Una de las caracteristicas mas importantes en las antenas es la ganancia.
Las antenas suelen ser muy direccionales, su energía es propagada en mayor cantidad en unas direcciones que en otras;
La ganancia es la relación entre la cantidad de energía propagada en estas direcciones en comparación con la energía que se propaga si la antena no es direccional

¿Como se consigue directividad?

La directividad se consigue cuando hay relacion entre la intensidad de radiación de una antena en la mejor dir ección y la intensidad de radiación de una antena isotrópica que radia con la misma potencia total.

Las antenas YAGI son las antenas conocidas como antenas direccionales formada por elementos como son los dipolos, un reflector y unos cuantos directores, normalmente el reflector suele ser 5% mas largo que el dipolo y sus directores algo mas cortos que el dipolo.
Asi con este diseño la ganancia y la direccionalidad mejoran.

Relacion delante-atras

La relacion delante-atras

Antenna Gain

Independent of the use of a given antenna for transmitting or receiving, an important characteristic of this antenna is the gain. Some antennas are highly directional; that is, more energy is propaga ted in certain directions than in others. The ratio between the amount of energy propagated in these directions compared to the energy that would be propagated if the antenna were not directional (Isotropic Radiation) is known as its gain.


Yagi

A Yagi-Uda is a directional antenna consisting of a driven element (typically a dipole or folded dipole) and additional parasitic elements (usually a so-called reflector and one or more directors). The reflector element is slightly longer (typically 5% longer) than the driven dipole, whereas the so-called directors are a little bit shorter. This design achieves a very substantial increase in the antenna's directionality and gain compared to a simple dipole

The front-to-back

The front-to-back ratio of an antenna is the proportion of energy radiated in the principal direction of radiation to the energy radiated in the opposite direction. A high front-to-back ratio is desirable because this means that a minimum amount of energy is radiated in the undesired direction.

Beam Width

The angular range of the antenna pattern in which at least half of the maximum power is still emitted is described as a „Beam With”. Bordering points of this major lobe are therefore the points at which the field strength has fallen in the room around 3 dB regarding the maximum field strength. This angle is then described as beam width or aperture angle or half power (- 3 dB) angle