Hi.
Have two eight feet diametre dishes in my yard; and wondering how low in frequency can be used.
Played a while with 2.4GHz wifi, 4GHz and 12GHz for satellite reception, and wondering how to 'compress' what lower frequency antenna into the focal region keeping somewhat decent performance. Gain nears 40dB at highest ranges.
Looking for some interesting activities... EME ? What else ?
-Yes, I have two amateur licenses-

 

Hello,

This page has a calculator, note that the dimentions are in meters:
https://www.satellite-calculations.com/Satellite/gain_bw.htm

The wiki shows the formulas:
https://en.wikipedia.org/wiki/Parabolic_antenna

Bertus