Ham Radio General Class Practice Test

Which of the following would increase the bandwidth of a Yagi antenna?

1. Larger diameter elements

2. Closer element spacing

3. Loading coils in series with the element

4. Tapered-diameter elements

The correct answer is: Larger diameter elements

Increasing the bandwidth of a Yagi antenna can be achieved through various modifications. Larger diameter elements are effective in achieving this because they reduce the Q-factor of the antenna. A lower Q-factor indicates a broader bandwidth, as it results in less energy being stored in the antenna and more being radiated as a wider range of frequencies. When the diameter of the elements is increased, this causes more lossless radiation and therefore helps to spread the frequency response, providing a wider operational bandwidth. This principle is crucial in antenna design, as it helps ensure that the antenna performs well across a range of frequencies, which is particularly beneficial for versatile communication applications. In contrast, closer element spacing tends to narrow the bandwidth because it can increase interaction between elements, while loading coils typically restrict bandwidth by adding reactance. Tapered-diameter elements can also affect bandwidth, but not as directly as larger diameter elements.