Optical SETI Map Conferences Map Illustrations Map Photo Galleries Map Observations Map Constructing Map
Search Engines Contents Complete Site Map Tech. Support Map Order Equip. Map OSETI Network

Search WWW Search www.coseti.org Search www.oseti.net Search www.photonstar.org Search www.opticalseti.org

colorbar.gif (4491 bytes)


Antenna Gain & EIRP




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

G = ------


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



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


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

Home Glossary
SPIE's OSETI I Conference SPIE's OSETI II Conference
SPIE's OSETI III Conference
The Columbus Optical SETI Observatory
Copyright , 1990-2006 Personal Web Site:
Last modified:  10/28/06
Contact Info