What is Antenna Directivity?

Directivity is the measure of the concentration of an antennas's radiation pattern in a particular direction. Directivity is expressed in dB. The higher the directivity, the more concentrated or focussed is the beam radiated by an antenna. A higher directivity also means that the beam will travel further.

An antenna that radiated equally well in all directions would be omni-directional and have a directivity of 1 (0 dB).

Gain is the product of directivity and efficiency. Where efficiency accounts for the losses on the antenna such as manufacturing faults, surface coating losses, dielectric, resistance, VSWR, or any other factor.

A high directivity is not always better, for example, many applications like mobile devices require omni-directional antennas and thus require antennas with a low/no directivity. High-directivity antennas are used in permanent installations such as satellite television, wireless backhaul etc. as they need to transmit and receive information over longer distances, in a particular direction.

Depending upon the physical construction of an antenna, every antenna has a three dimensional radiation pattern. This can either be Omni directional or directional in respect to plane parallel to earth. Any antenna with a radiation pattern that is less than 360° in such a plane, is known as a directional antenna. This means that a directional antenna will radiate and receive more effectively in a specific direction, which is true of all practical antenna. For example, a dipole antenna is an Omni directional antenna, where a Yagi antenna or parabolic antennas are directional. Directivity is a measure of how directional an antenna is. Directivity is typically given as the peak directivity of the main lobe of the antenna’s radiation pattern.