Which preposition to use with radar

as Occurrences 1%

It appeared on radar as a faint blip, allowing the Earth ships to locate it without difficulty.

in Occurrences 1%

"The pirates should be seeing that on their radar in a few minutes," said Zip.

within Occurrences 1%

Even if they could pilot the ship, it was certain that the pirates would locate them by radar within seconds of their departure and the chances of their escape would be practically nil.

Which preposition to use with  radar