A T-aerial is an antenna (radio)

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 used for VLF, LF, MF and shortwave

Shortwave

Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 transmission or reception.

It consists of a horizontal wire suspended between (and insulated from) two radio masts or towers

Radio masts and towers

Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...

. A vertical wire is connected to the middle of the horizontal wire and hangs down close to the ground, where it is connected to the transmitter or receiver. The two wires form a T shape, hence the name.

Sometimes a group of parallel wires, known as a cage, is used instead of a single wire. This reduces the Q factor

Q factor

In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency....

 of the antenna and broadens the bandwidth over which it will provide good impedance matching

Impedance matching

In electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or minimize reflections from the load....

.

T-aerials are frequently used as transmitting aerial for long and medium wave broadcasting.