When TV changed over from the NTSC analog to the new HDTV digital, the same frequencies were used except a portion of the highest UHF frequencies were taken away for other uses. This means that an old analog combination VHF/UHF antenna works fine with the new HDTV. From a technical perspective, the term "Digital" added to "Antenna" is meaningless. Digital antenna is only a marketing term to make someone think it is better.
Don't think that hooking multiple antennas together will help. There are a lot of technical issues that I won't get into (some of the same nature as Amelia problems with the antenna changes on her plane just before her last attempt). In the old analog days it might have helped, but with the new digital signals are easily distorted by phase delays and multipath. It comes down to the modulation scheme chosen by the committees for the new digital signals. Some technical experts claim that cable companies used their influence in the modulation method that was approved so that the new digital over-the-air method would be more susceptible to multipath (multiple signals from the same station arriving at the antenna, but different path lengths i.e phase delay - direct signals and signals reflected off tall buildings). The cable companies wanted to insure that in large metropolitan areas (lots of tall buildings) where the TV signals are the strongest, the signal distortion would increase the number of people choosing to pay for cable.
When you see a strong signal, but your TV picture occasionally freezes, breaks up into blocks, looks like cubist artwork, and then returns to a strong signal again, you can usually blame multipath. I have the issue with cars passing in front of my house. Even though I don't have cable, I blame the cable companies for my TV reception issues! I only pay the cable companies for internet, and the price for just that has slowly crept up to the point that I am considering other internet options.
Hey - I got Amelia into my reply to this thread!