Counterpoise (ground system)

The ground serves as a capacitor plate to receive the displacement current from the antenna element and return it to the feedline from the transmitter.

A common design for a counterpoise is a series of radial wires suspended a few feet above the ground, extending from the base of the antenna in all directions in a "star" pattern, connected at the center.

[2] Since the radio frequency alternating currents from the transmitter can pass through a capacitor, the counterpoise functions as a low-resistance ground connection.

There should not be any closed loops in the wires of a counterpoise system, as the strong fields of the antenna will induce circular currents in it which will dissipate transmitter power.

However, at low frequencies, the resistance of even a good ground system in high conductivity soil can consume a major portion of the transmitter power.

Another source of resistance is dielectric losses from the penetration of radio waves into the ground near the antenna due to the large skin depth at low frequencies.

Ground screen, similar to a counterpoise, at base of mast antenna of AM radio station KTBS
Diagram of counterpoise under the antenna mast of an AM radio station. It consists of a network of radial copper wires suspended above the ground, connected to the transmitter feedline ground. It is suspended about 8 feet above ground, so technicians can get access to the helix house at the foot of the tower.
Antenna used in Lodge-Muirhead wireless system around 1900, the first counterpoise.
Inverted-L antenna with counterpoise, in a powerful amateur radio station, Colorado, 1920. The counterpoise is the lower grid of horizontal wires, suspended below the antenna.