Caracteristicas de las antenas.

Características de las antenas.

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 de antena.

Independientemente del uso dado a una determinada antena para transmitir o recibir, una característica importante de la antena es la ganancia. Algunas antenas son altamente direccionales; esto es, se propaga más energía en ciertas direcciones que en otras. El ratio entre la cantidad de energía propagada en esas direcciones comparada a la energía que sería propagada si la antena no fuera direccional (radiación isotrópica) es conocida como su ganancia.

¿Como se consigue directividad?

Se consigue directividad añadiendo al dipolo elementos reflectores y directores como en las antenas Yagi

al colocar los elementos reflectores y directores consigo un diagrama de radiación con mayor directividad como se muestra en la imagen.

La antena Yagi

 

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.



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 Ratio

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 Width”. 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