A passive radiator or parasitic element is a radio antenna element which does not have any wired input. Instead, it absorbs radio waves radiated from another active antenna element in close proximity, and re-radiates it. This will change the antenna pattern and coverage area somewhat, though not as much as an active element.

This same effect happens in everyday life, as anything metal near a radio or television set can distort signals in this manner. Likewise, people and larger animals like pets can do the same, as they contain about 70% water, which also conducts radio waves.