What is the smallest size of radio telescopes?
One thing is certain: all of the radio telescopes positioned in space exploration centers have one thing in common. nThey are all colossal in size. A radio telescope with a wavelength between 3 and 30cm can have a diameter of more than 100 meters.
The diameter of radio telescopes that operate in the wavelength range 30cm to 90cm can vary between 3 and 90 meters. You may build a functional radio telescope on your property and use it as you desire.