In order to receive digital TV signals from all stations your antenna should be able to receive both VHF and UHF channels.  Indoor TV antenna commonly known as "rabbit ears" need to be augmented with an additional "loop" antenna in order to pick up signals in the UHF range.

Before shopping for a new digital TV antenna try your existing antenna first as you might find to your surprise that it actually can pick up UHF signals. If you don't try you'll never know would you?

You could also check to see if your existing antenna works by using your digital to analog converter box or digital TV to see if you can receive digital signals.  Digital TV reception can be improved by moving the digital TV antenna even if it is only a couple of inches but make sure to move it slowly as it takes time for the new signal to be detected.