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

Antenna bandwidth is the range of frequencies over which the antenna maintains an acceptable SWR and performance. The physical thickness of the antenna elements is a primary factor in determining this bandwidth. Using elements with a larger diameter reduces the antenna's Q factor (quality factor). A lower Q factor flattens and broadens the resonance curve, thereby increasing the usable bandwidth. Other options, such as closer element spacing or adding loading coils, generally narrow the bandwidth or are used for physical shortening rather than increasing the frequency range.