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Antenna Gain & EIRP

9006-003

 

9006-003a


The gain of a 100% efficient antenna over an isotropic radiating or receiving antenna is given by:

 
    4.pi.A
G = ------
      Wl2
 

where:

A = At for area of transmitting antenna or telescope (78.5 m2),
A = Ar for area receiving antenna or telescope (78.5 m2),
Wl = wavelength (656 nm).

 

The gain is normally expressed in dBs by taking 10.log(G).

For the above 10 meter diameter telescope:

 

G = 2.29 x 1015 = 153.6 dB

 

9006-003b


The Effective Isotropic Radiated Power (EIRP) is the apparent power transmitted towards the receiver, if it is assumed that the signal is radiated equally in all directions, i.e. as a spherical wave emanating from a point source. This power is given by:

 
EIRP = Gt.Pt  Watts
 

where:

Gt = gain of transmitter antenna or telescope (153.6 dB),
Pt = power transmitted (1 kW).

 

For the above 1 kW visible transmitter:

 

EIRP = 2.29 x 1018 W

 

This is a little over one million trillion watts! Now the Sun has a radius of 6.96 x 108 m and a luminosity of 3.9 x 1026 W. Thus the output from every square meter of the Sun's surface is equal to 64 megawatts. Clearly, the spectral radiance of this 1 kW visible transmitter is enormous.

 

The Columbus Optical SETI Observatory
Copyright (c), 1990

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Last modified:  10/28/06
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