Hi Guys,
You might be interested in some experiments I did with something similar a couple of years back.
http://www.threehillsobservatory.co....stronomy_1.htm
You can detect the microwaves from the black body spectrum of the sun and moon (and people if they stand in front of the dish) but I found it is not sensitive enough (the Ku band frequency is too high really) or stable enough to detect anything more distant.
Cheers
Robin