A ground-plane antenna, also called a quarter-wave or a monopole antenna, is widely used in radio communication systems. It is relatively simple in design and consists of a vertical conductor, typically a metal rod or wire, mounted above a conducting surface known as the ground-plane. The ground-plane acts as a mirror or a reflector for the radio waves, enhancing the antenna's performance. The ground-plane can be a large conducting surface, such as a metallic roof, the body of a car, or a set of radial wires or rods extending horizontally from the base of the vertical element.
It is called a quarter-wave antenna because its physical length is one-quarter of the wavelength of the radio waves. The following formula determines the length:
Note
Where: \(C\) = speed of light. \(f\) = Frequency. \(λ\) = wavelength. \(V_f\) = the velocity factor of the material used. \(L\) = length of the vertical element.
Ground-plane antenna uses typically include ham radio, CB, WiFi, base station antennas, and mobile communication. They are also found in aviation communication and many other wireless applications.
Velocity factor
The velocity factor in the formula depends on the type of conductor you are using and the type and thickness of the insulation. Velocity factors range from about 0.93 to about 0.98. For best results, use bare copper. The default velocity factor in the following calculator is 97%, corresponding to uninsulated copper wire. You might have to trim the elements slightly to get the antenna resonant at your desired frequency.
Easy to build
A ground-plane antenna's key advantages are its simplicity, good matching, and ease of installation. The absence of complex matching networks or additional elements makes it cost-effective and efficient for countless applications. It is an actual unbalanced antenna with a feed impedance of around 50Ω. The 50Ω impedance can be reached by adjusting the radials to an angle between 42º and 45º.
Overall, the ground-plane antenna is straightforward with an effective design that provides reliable communication capabilities, making it a popular choice in numerous wireless systems.