If your HDTV does not have a coaxial cable input, you will likely need a Digital TV Tuner set top box in order to receive free over-the-air digital broadcasts. Something like this
Digital 1080p HD DTV Tuner should be what you're looking for.
Caveat: I have no experience with this device and have no idea if it will work in your area. Specifications say it should work, reality may be different.
-Wolf sends