NTSC, ATSC HD and whatever 4k format is eventually chosen are all sent as formats on a carrier signal. That signal is on the TV bands which range from 54 MHz to around 600 MHz. The TV antenna is a tuned piece of wire which is designed to receive signals at that frequency. The decoding of the signal occurs in the TV or external tuner.
Basically, any antenna that is tuned for these frequencies will receive old TV, current TV or future TV signals. Yeah, I know scum companies will be out there trying to sell special HD or 4K antennas. It is total BS and in most cases those antennas will not work as well as the one you already have.