Ganancia:
En la imagen de la figura veo el diagrama de radiación de un dipolo, puesto en comparación con un diagrama de radiación isotrópico (antenas omni direccionales).
Ganancia es la relacion entre la tension maxima captada por la antena y la tension maxima captada por una antena de referencia de ganancia unidad. Algunas antenas son direccionables: se propaga mas energia en unas direcciones k en otras. El ratio entre la cantidad de energia propagada en esas direcciones comparada a la energia que seria propagada si la antena no fuera direccional (isotropica).
¿Como conseguir derectividad?
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 es una antena YAGI
Relacion delante/atras: Es la relación entre la ganacia en la direccion maxima de radiación y el valor en la dirección opuesta.
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 propagated 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. When a transmitting antenna with a certain gain is used as a receiving antenna, it will also have the same gain for receiving.
Antena YAGI
Yagi antenna, 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.
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
