The biggest UHF TV transmitter I know uses 10 off 50 KW peak sync power, i.e. 500KW. The input to the aerial will be 50 ohms. So V^2/50 = 500,000 so V = 5,000 and the current 100A. This is a problem for the aerial feeders as the coaxial cable has to withstand this voltage so it has to be very large in diameter. if its very large in diameter, the the RF treats the gap between the inner and outer conductors as a wave guide if the frequency is too high.
The smallest TV transmitter is about 1W for filling gaps in coverage due to shadow effects in valleys.
Should say you are thinking of receiver antennas but didn't actually tell that.you are talking about transmitter. But i was referring to the power generates in TV antenna at the receiver for UHF and VHF.