radio beacon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A fixed radio transmitter that broadcasts distinctive signals as a navigational aid.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun communication A beacon that emits radio wave signal to guide ships and/or aircraft.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a characteristic signal emitted by a transmitter used for navigation
• noun a radio station that broadcasts a directional signal for navigational purposes