Winegard Sensar Pro, has several modes, In sleep mode it is powering two amplifiers (the original batwing amp and it's own internal amp) and as I recall is drawing less than 1 amp.. However that said the ON-Line manual does not list the reqirements.
The paper one in my motor home, about half a mile away, does.
But the question is not how many amps, but how many Miliamps (1/1000th amps) It does not draw much.
EXCEPTION: Some very old antennas can go into osclation, causing all sorts of interference, The odds you have one of these approaches zero (Far as I know they have ALL been replaced so the odds are zero but my knowledge is not absolute)
IF you really need to know, break out the mulit-meter,, Find the fuse that feeds it (or simply remove the wall plate with the 12 volt outlet, switch, led and antenna connector and pull one of the 12 volt wires off)
Put the meter in series, choose the highest current range UNDER 10 amps and go down till you get a useful reading.
Home is where I park it!