Ham Radio General Class Practice Test

What is the approximate length of the driven element of a Yagi antenna?

1. 1/4 wavelength

2. 1/2 wavelength

3. 3/4 wavelength

4. 1 wavelength

The correct answer is: 1/2 wavelength

The driven element of a Yagi antenna is typically designed to be approximately 1/2 wavelength long. This length allows the driven element to efficiently convert the RF energy supplied by the transmitter into electromagnetic waves, which are then radiated into space. When an element is a half-wavelength long, it achieves resonance and provides optimal performance in terms of gain and bandwidth. The resonance occurs because the length of the element matches the wavelength of the frequency it is designed to transmit or receive. This resonant condition is essential for effective radiation and reception of radio waves. In contrast, different lengths such as 1/4 wavelength, 3/4 wavelength, or full wavelength do not provide the same level of efficiency and effectiveness for the driven element within the context of a Yagi antenna's specific design and function. A 1/4 wavelength element is typically used for other applications, while 3/4 wavelength and 1 wavelength configurations do not align well with the optimized design criteria for Yagi antennas. Thus, a half-wavelength is the standard that ensures the antenna operates efficiently within its intended frequency range.