Some good info on dish antennas can be found here. The key to high gain is to have a narrow beamwidth. Many simple dish antennas have beamwidths as wide as 14 degrees. Most high powered satellite and radar antennas have much narrower beams and much higher gains. Some of the Air Force Satellite Control Network (AFSCN) antennas we used to control satellites had a beamwidth of 0.1 degree and a gain of 63 dB, or a multiplication factor of 2 million. Narrow beamwidth parabolic dish antennas frequently have gains well in excess of 50 dB (100,000). As for radars, it depends on the type of radar you're talking about. Search type antennas used for things like air traffic control emit a narrow vertical beam of energy. Tracking antennas used for things like air defense emit very narrow spot beams.

The key factor to consider is EIRP (Effective Isotropic Radiated Power).

Other references:

Antenna Models

CAMRa radar specs

Antenna Gain and EIRP

ESA Uplink Stations. Note that the EIRP ratings for these antennas are all over 60 dBW, or an effective 1 million watts. One of them has an EIRP of 71 dBW (~12.6 million watts). The uplinks available here are even more powerful at 75 dBW (~31.6 million watts).