Not so very long ago, the public was told that they could no longer use an antenna to obtain our television broadcasts. The truth of the matter is that we can no longer receive analog signals in the traditional manner. But we can receive digital signals.
Yes, this means you can use an antenna. But what about high definition channels? How might we obtain those with an antenna? The quick answer is that you can't. The long version is you can't, at least not without an upgraded antenna.
A high definition antenna will deliver high definition programming over the air (OTA). If you'd like an even better option, get one that's meant to go outside, a la the old style roof mounted television antennas.