ABSTRACT

The radiation intensity is the power-per-unit solid angle in the direction and denoted by . The average radiation intensity over radians (solid angle) is the total power divided by . Hence, Eq. (15.1) can be written as

It follows that

As an approximation, it is customary to rewrite Eq. (15.3) as

where and are the antenna half-power (3-dB) beamwidths in either direction. The antenna power gain and its directivity are related by

where is the radiation efficiency factor. In this book, the antenna power gain will be denoted as gain. The radiation efficiency factor accounts for the ohmic losses associated with

GD G Ae

GD maximum radiation intensity average radiation intensity

--------------------------------------------------------------------------------=

   P    4

4

GD 4 maximum radiated power unit solid angle 

total radiated power -------------------------------------------------------------------------------------------------------------------------------------=

GD 4 P   max

P    d d 0

 ---------------------------------------=

GD 4 33----------

3 3

G rGD= r

the antenna. Therefore, the definition for the antenna gain is also given in Eq. (15.1). The antenna effective aperture is related to gain by

where is the wavelength. The relationship between the antenna’s effective aperture and the physical aperture is

is referred to as the aperture efficiency, and good antennas require (in this book is always assumed, i.e., ).