It’s a regular UHF antenna that has been named a “4K” antenna by someone in “marketing” who realized that many people are buying new 4K TVs, and will need antennas to go with them.
Most digital TV broadcast channels are in the UHF channels. Some are in the VHF channels. That’s why the old “rabbit ears and loop” antennas from the 70s and 80s will function to receive these signals.
4K TV Antennas for 4K TV Shows?
Nope. Sorry. There are no 4K broadcasts yet. So if you get a 4K TV you need a source of 4K TV. That means satellite TV, cable TV, internet streaming services, or 4K discs.
Odds are, you will not even get great 4K programming, because the digital channels are still the same – the amount of data transmitted is limited, and the broadcasters need to make business decisions about how much signal a TV show gets.
Some of the technical details about digital “channels” are described in HDTV Data Multiplexing by Peter Putnam from back in the early days of digital TV. Digital TV already requires MPEG-2 compression to fit 1080i/60 broadcasts into TV channels. Compression = removing some picture quality.
Additionally, according to 4K HDR Compression and Compromises: Something’s Gotta Give by Jeff Boccaccio, 4K TV itself starts to touch some physical limits of copper wires to carry the picture signal. So, like HDTV, it requires compression, but also needs better cables that match a new technical standard, and likely need fiber optic cables, which don’t yet exist.
The standard to broadcast 4K TV, also called NextGen, is called ATSC 3.0. As of January 2019, ATSC 3.0 is still being defined.
This is another way to say: as of 2018 4K TVs exist, and new 4K HDMI cords exist, and some 4K programming exists, and some is delivered over cable or satellite, using proprietary standards, but the standards to broadcast 4K programming over terrestrial radio don’t exist, which means that 4K TV stations don’t exist.