Television antennas are comprised of a series of metal rods cut to exact lengths and positioned so they receive a particular television frequency. The following design was invented in the 1960s by an engineer named Doyt Hoverman. It is particularly sensitive in the UHF frequency range, the same range used for the majority of digital television transmissions.
This coat hanger antenna isn’t a project of my making, I merely wanted to comment on it in this space. All credit goes to Make:television for posting the (attached) instruction PDF.