Directivity describes the directionality of the radiation pattern of a
sensor element or array of sensor elements.
Higher directivity is desired when you want to transmit more radiation in a specific
direction. Directivity is the ratio of the transmitted radiant intensity in a specified
direction to the radiant intensity transmitted by an isotropic radiator with the same total
transmitted power
where
Urad(θ,φ) is the radiant
intensity of a transmitter in the direction (θ,φ) and
Ptotal is the total power transmitted by an
isotropic radiator. For a receiving element or array, directivity measures the sensitivity
toward radiation arriving from a specific direction. The principle of reciprocity shows that
the directivity of an element or array used for reception equals the directivity of the same
element or array used for transmission. When converted to decibels, the directivity is
denoted as dBi. For information on directivity, read the notes on Element Directivity and Array Directivity.
Computing directivity requires integrating the far-field transmitted
radiant intensity over all directions in space to obtain the total
transmitted power. There is a difference between how that integration
is performed when Antenna
Toolbox™ antennas are used in a phased
array and when Phased Array
System Toolbox antennas are used. When
an array contains Antenna
Toolbox antennas, the directivity computation
is performed using a triangular mesh created from 500 regularly spaced
points over a sphere. For Phased Array
System Toolbox antennas,
the integration uses a uniform rectangular mesh of points spaced 1°
apart in azimuth and elevation over a sphere. There may be significant
differences in computed directivity, especially for large arrays.