When constructing a field expedient ground plane antenna, what is the recommended length for the vertical and ground plane elements?

In the design of a field expedient ground plane antenna, the recommended length for both the vertical and the ground plane elements is one-quarter wavelength of the desired operating frequency. This length is particularly effective because a ground plane antenna relies on the combination of the vertical element, which acts as the radiating element, and the ground plane elements, which effectively act as reflectors to enhance the radiating efficiency.

When each element is one-quarter wavelength, it optimizes the impedance characteristics and matching with the transmission line, leading to better performance in terms of radiation pattern and efficiency. At this length, the antenna can produce a strong signal and a desirable pattern with minimal losses.

Choosing lengths different from one-quarter wavelength, such as one-eighth, one-half, or full wave, would not yield the same advantage in terms of efficiency and radiation pattern. A one-eighth wave element would be too short, resulting in a poor match, while a one-half or full wave would lead to an inefficient antenna design with the potential for increased ground losses and unpredictable radiation characteristics. Thus, using a quarter wave length for both the vertical and ground plane elements is a widely accepted practice in antenna design, especially for expedient setups.