thumb|[[KVLY-TV mast]]
Radio masts and towers are typically tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.
A mast radiator or radiating tower is one in which the metal mast or tower itself is energized and functions as the transmitting antenna.
==Terminology==<!-- This section is linked from List of tallest structures in the world -->
thumb|right|A radio mast base showing how virtually all lateral support is provided by the guy-wires
The terms "mast" and "tower" are often used interchangeably. However, in structural engineering terms, a tower is a self-supporting or cantilevered structure, while a mast is held up by stays or guy-wires.
; A mast: is a guyed mast, a thin structure without the sheer strength to stand unsupported, that uses attached guy lines for stability. They may be mounted on the ground or on top of buildings. Typical masts are of steel lattice or tubular steel construction. Masts tend to be cheaper to build but require an extended area surrounding them to accommodate the guy wires.
; A tower: is a self-supporting structure, possibly also placed on a rooftop, that accomplishes the same purpose of raising actual radiating antennas to a functional height. Since it does not require land area from which to anchor guy lines, towers are more commonly used in cities where land is in short supply.
thumb|left|The [[Tokyo Skytree was, in 2012, the tallest freestanding tower in the world]]
There are a few borderline designs that are partly free-standing and partly guyed, called additionally guyed towers. Examples:
; Gerbrandy tower: consists of a self-supporting tower with a guyed mast on top.
; Blaw-Knox towers: Those few of the towers still standing do the opposite: They have a guyed lower section surmounted by a freestanding part.
; Zendstation Smilde: is a tall tower with a guyed mast on top with guys which go to ground.
; Torre de Collserola: is a guyed tower with a guyed mast on top where the tower portion is not free-standing.
History
The first experiments in radio communication were conducted by Guglielmo Marconi beginning in 1894. In 1895–1896 he invented the vertical monopole or Marconi antenna, which was initially a wire suspended from a tall wooden pole. He found that the higher the antenna was suspended, the further he could transmit, the first recognition of the need for height in antennas. Radio began to be used commercially for radiotelegraphic communication around 1900.
thumb|Multiwire broadcast [[T-antenna of early AM station WBZ, Springfield, Massachusetts, 1925.]]
AM radio broadcasting began around 1920. The allocation of the medium wave frequencies for broadcasting raised the possibility of using single vertical masts without top loading. The antenna used for broadcasting through the 1920s was the T-antenna, which consisted of two masts with loading wires on top, strung between them, requiring twice the construction costs and land area of a single mast.
He found that the radiation resistance increased to a maximum at a length of so a mast around that length had an input resistance that was much higher than the ground resistance, reducing the fraction of transmitter power that was lost in the ground system without assistance from a capacitive top-load. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached a maximum at a mast height of