Yes and no. In the first place, there is no such thing an an HD antenna. A TV antenna is a TV antenna, period. No antenna cares whether the signal it receives is analog or digital, it works exactly the same way.
Now, assuming your plasma TV is an HD set, your cable is an obvious source for HD programming. You just need a subscription to the right channel package and an HD set top box.
If you don't like the expense of that, you can leave the cable and go with an over the air (OTA) antenna for free HD from your local broadcast stations. But if you make that choice, be aware that you do need a very good OTA antenna unless you are really close to the TV transmitting towers. Very good for most people means, realistically, outside rather than inside, as high as possible, and on a rotor if your stations are in different directions from you. Check the references for guidance if you're considering OTA.
