Counterpoises are part of the antenna — wires or metal tubes acting as an artificial ground, enhancing the antenna's efficiency. They are used instead of conventional grounding and serve to reduce the physical size of the antenna. The counterpoises of a stationary antenna are connected to the outer part of the antenna connector of the station (amplifier) or to the "Ground" contact; for vertical elements — to the grounded base part.
Typically, counterpoises in the form of structural antenna elements (radials, discs, mesh structures) are used in stationary antennas. For mobile antennas, the vehicle body serves as the counterpoise (artificial ground). For handheld radios, the operator's body acts as the ground (counterpoise).
Counterpoises are classified as resonant and non-resonant. Resonant counterpoises have a specific length that allows them to resonate with the signal radiated by the antenna. Depending on the antenna type, resonant counterpoises may be quarter-wave, half-wave, etc. Resonant counterpoises are the most efficient for antenna operation. Non-resonant counterpoises have arbitrary lengths and are not tuned to resonance with the antenna's radiated signal.
Some antenna designs do not include classic counterpoises in the form of radials extending outward, such as collinear antennas. These “counterpoise-free” antennas have a stronger mechanical design and are easier to install.
Related articles: stationary antenna, SWR, Radiation Pattern, Wave Polarization.