What is happening next year in the TV world is that all analog broadcast will end. Digital broadcasts, Which are already there, will continue, and/or increase.
Now: The antenna. There is no such thing as a "Digital" (or Analog) antenna, there are only RF-Antennas. it's all the same to the antenna. The antenna could care less if it's digital or analog.
The only thing the antenna worries about is the wavelength (or if you like the frequency) Antennas like a fairly small slice of the frequency spectrum. The Television portion is divided into 3 parts: VHF-low (Channels 2,3,4,5,6) VHF-HIGH (7-13) and UHF 14-69)
Digital will be using the UHF band, 14-59 for most markets, in some of the more dense markets they may also use VHF-High (7-13)
So... Your existing antenna, if it works for UHF, will continue to work, You will need to either replace the TV or put an adapter in front of it unless it's already digital ready (I'll tell you how to figure that out in a bit)
What won't work, in all markets, is the piece of junk that is being sold at rallies and on the internet for around 99.95.. It is a 20 dollar UHF only antenna. So if you are in one of the saturated markets.... You will not get all the stations. But odds are your existing antenna will do just fine (There is one Wineguard model that needs a UHF upgrade)
How to tell if your TV is Digital ready.. ASK IT.
Often if they say are they will say so, on the front, or back (look for either "Digital" or the letters ATSC)
Look at your remote.. If there is a "Guide" button.. Good chance it's digital
Try to tune to a channel like 20-2 or 7-1 (pick a station that you can see, 20 and 7 are both active here in Detroit) But if you are watching say channel 5, then try to tune in 5-1.. If you don't have a "-" key (NOTE: some remotes may have a "." key in which case it's 5.1) then it's NOT digital.
On my digital adapter when I press "guide" it shows me the current show, and the next show no the existing channel (different sets will be different) Just so you know.
But if your antenna works for UHF now, IT will continue to work for UHF for a long time to come unless it's damaged or just plain fails (happens some times) from the antenna's point of view.. Nothing is changing at all.