The Ground Plane Antena

A typical mobile cb antenna does not transmit horizontally it radiates in a downward pattern.

The ground plane antena. The image is a tool for understanding the earth s effect on patterns. A ground plane antenna is a form of dipole antenna designed to work with an unbalanced feed line. I know that an antenna that has half a wavelength does not need the ground plane example a dipole antenna and when using a wavelength of 1 4 it is usually necessary to have the ground plane planar antennas pcb. I can t understand why we need to use a ground plane at 1 4 wavelength and not at 1 2 wavelength.

In telecommunication a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna to reflect the radio waves from the other antenna elements. Often the conductor is simulated by a number of radials often a quarter wavelength long. Clarification needed ground plane shape and size play major roles in determining its radiation characteristics including gain. Read more about the antenna ground plane.

The image antenna just represents all of the currents induced in the ground all around the antenna. Ease of fabrication and cost makes the ground plane antenna one of the popular antennas in communication systems. A ground plane antenna is a variant of the dipole antenna designed for use with an unbalanced feed line such as coaxial cable. An antenna ground plane is not to be confused with an electrical ground.

What is an antenna ground plane. Since the image is 180 degrees out of phase with the antenna and effectively the same distance below ground as. There are two or more radials each measuring 1 4. Ground currents all around the antenna make the image work.

Ahh the good old quarter wave ground plane. This is a simulated ground made from a sheet of conductor which typically extends out to a quarter wavelength from the antenna. This calculator can be used to design a quarter wave ground plane antenna with radials. The horizontal radiation pattern is a circle where the antenna radiates equally well in all directions.

A ground plane antenna is more of less one half of the dipole and mounted above the ground plane. It resembles a coaxial antenna whose lower section consists of straight elements called radials instead of a hollow conducting cylinder. It is found that for a monopole antenna like a quarter wavelength vertical the ground acts as a plane to reflect the radio waves so that an image of the top half of the antenna is seen in the earth. The ground plane antenna is omnidirectional.

As the name indicates the antenna ground plane acts as a simulated ground. Figure 6 shows the vertical radiation pattern. The radiating element is a quarter wave λ 4 and the radials are 12 longer. Many vertical antennas employ what is called a ground plane.

A metal surface the larger and flatter the better is required underneath the cb antenna to launch the signal out into the atmosphere.