An off air HD antenna is not any special kind of antenna. It is just a normal type of aerial for VHF or UHF reception. The digital data is transmitted from the station either on UHF or VHF frequency band and is received by the antenna. Today the HDTV channels are mostly broadcasted on the UHF band.
The best off air HD antenna for you setup depends on the distance, directions, transmitter's power, height of the transmitter, type of terrain between your antenna and transmitter, buildings and the transmission path. These factors contribute to the strength or weakness of the signals that you receive. A good choice antenna will be an outdoor VHF/UHF antenna with a good size. If the transmission path is not obstructed then a multidirectional antenna works well and in case of building, trees you require a directional antenna. In case of great distances or placing the outdoor antenna in the attic you will have to use a preamplifier as well.
Over-the-air HDTV is the best you can get
Off air HD antenna is the best way to catch the high resolution quality audio and video. There are many benefits related to off air reception. HD off air antenna reception produces best picture quality because there is no compression in screen resolution and audio. Almost 99% of the people can receive one digital station and 89% can receive 5 stations in the cities. In case someone lives in a large city he will be able to pull in many digital stations with his off air HD antenna for free.
The antenna is engineered to receive local HDTV channels, with an operating bandwidth covering either the VHF (channels 2 to 13) or UHF (channels 14 to 69) frequency ranges or both (see specifications above).