Master Thesis

2.5.5 Directivity
Figure 2.7 Spherical Coordinate Systems for Antenna Analysis
Directivity is “the ratio of the radiation intensity in a given direction from the antenna to the
radiation intensity averaged over all directions” (IEEE, 1993). It is a function of direction but
it is often defined only to the direction of the major lobe Directivity can be expressed as
Where ω is the radiation density per solid angle and pt is the total power transmitted by the
antenna and is the solid angle (Lindell & Nikoskinen, 1995).
2.5.6 Gain
The directivity was defined from the radiation intensity in the main beam direction and the
total radiated power. The antenna gain has the same definition, except that the total
radiated power is replaced by the total power delivered to the antenna port [1]. This may be
expressed by using the directivity as
Where erad is the total radiation efficiency and epol is the polarization efficiency.
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