What is antenna directivity?

• A. The electrical length of the antenna.
• B. The antenna radiation pattern or how focused it is.
• C. The impedance matching quality.
• D. The total power delivered to the antenna.

Answer: (B)

Directivity describes how focused the antenna’s radiated energy is in particular directions, as shown by its radiation pattern. It compares the power radiated in a given direction to the average power radiated in all directions (an isotropic radiator). A high directivity means most of the energy is concentrated into a narrow beam, while low directivity means energy is spread more evenly. This property comes from the antenna’s physical size and shape relative to the wavelength, not from how long the antenna is electrically, nor from how well the feed is matched, nor from the total power you drive into the antenna. Impedance matching affects how much power actually gets to the antenna, and total power is about input power, while directivity specifically describes the directional distribution of that radiation.