Practical_Antenna_Handbook_0071639586

C h a p t e r 2 1 : A n t e n n a N o i s e T e m p e r a t u r e 495
In a typical system (Fig. 21.1) the main lobe will be pointed toward the sky noise
source, while the sidelobes will pick up noise from the ground. The total noise temperature
of the antenna is thus
T = ( M × T ) + ξ(1 – M ) T + T
ANT SKY GND R (21.10)
where T ANT = equivalent noise temperature of antenna
T SKY = noise temperature of sky
T GND = noise temperature of ground
= feedpoint loss resistance noise temperature
T R
M
x
= fraction of total energy that enters main lobe
= fraction of sidelobes that are viewing the ground (only one of several
sidelobes is shown in Fig. 21.1)