Hi All,

Modern engineering text indicates that for the same frequency, a large
fully illuminated dish will provide more gain than it’s smaller
equivalent. Why is this ?

Consider the following scenario:

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Take a 10GHz RF source, and attach an appropriate feed horn to fully
illuminate a 2m dia dish.

Adjust focus so that the wave front out of the dish is parallel (2m
diameter ?)

At a distance, arrange the same setup, except the RF source is
replaced by a detector.

Make a note of received signal strength.

======

Repeat the same experiment at the same frequency, but with a
3mdiameter dish at each end, and appropriate feed horns .

Make a note of received signal strength.

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Also, see http://www.idesignz.org/misc/dishproblem.pdf

In both cases all of the TX energy is transmitted in a parallel beam,
whose diameter is the same as the respective dish.

It would seem that if you can fully convert all of the TX RF into
parallel waves, at some point the diameter of the dishes should not
make any difference to the transfer efficiency of the system.

So, why would the received signal for the 3m + 3m dish be greater than
that of the 2m + 2m dish experiment ?

Thoughts please.

Mark

http://www.idesignz.org/AMPS/AMPS_BS.html – Experimental AMPS micro
Base Station project

http://www.idesignz.org/UAV/index.html – Early work on the four rotor
FlyingThingy