A ‘T’-antenna, ‘T’-aerial, or flat-top antenna is a monopole radio antenna consisting of one or more horizontal wires suspended between two supporting radio masts or buildings and insulated from them at the ends. A vertical wire is connected to the center of the horizontal wires and hangs down close to the ground, connected to the transmitter or receiver. The shape of the antenna resembles the letter "T", hence the name. The transmitter power is applied, or the receiver is connected, between the bottom of the vertical wire and a ground connection.
A 1935 photo of WOR / 710AM's facility in Carteret, New Jersey. In this case there are three radiators: the two towers and the center ‘T’-antenna, suspended in the middle.
Multiwire broadcast T-antenna of early AM station WBZ, in Springfield, MA, 1925.
One of the first uses of ‘T’ aerials in the early 20th century was on ships, since they could be strung between masts. This is the antenna of RMS Titanic, which broadcast the rescue call during her sinking in 1912. It was a multiwire ‘T’ with a 50 metre (160′) vertical wire and four 120 metre (400′) horizontal wires.
An amateur radio cage ‘T’-antenna 60 ft high by 90 ft long built in 1922, owned by the Historic Radio Engineers Club, Riverhead, New York. The conductor is made of a 'cage' of 6 wires held apart by wooden spreaders. This antenna achieved transatlantic contacts on 1.5 MHz, at a power of 440 W.
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane.
The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.
A typical mast radiator monopole antenna of an AM radio station in Chapel Hill, North Carolina. The mast itself is connected to the transmitter and radiates the radio waves. It is mounted on a ceramic insulator to isolate it from the ground. The other terminal of the transmitter is connected to a ground system consisting of cables buried under the field.
Marconi's first monopole transmitter
One of Marconi's early monopole antennas at his Poldhu, Cornwall transmitting station, 1900, consisting of a small metal plate suspended from a wooden arm with a long wire running down to the transmitter in the building.
Multi-lobed radiation pattern of a 3/ 2 wavelength monopole. Monopole antennas up to 1/ 2 wavelength long have a single "lobe", with field strength declining monotonically from a maximum in the horizontal direction, but longer monopoles have more complicated patterns with several conical "lobes" (radiation maxima) directed at angles into the sky.
