A device used in radio astronomy to detect radio waves; also known as an aerial. In an antenna, radio waves induce an oscillating electric current in a conductor. The simplest antenna is a dipole antenna, which is a simple metal rod. More complex antennas, such as the Yagi antenna, may consist of a dipole or folded dipole (the driven element) with other conducting rods (parasitic elements) which direct or reflect the waves on to the dipole and so increase the antenna’s directivity and gain. The most powerful radio telescopes, especially at high frequencies, use parabolic (dish) antennas to collect waves and bring them to a focus. Large numbers of antennas may be combined in an array to achieve high resolution. Antennas may also be used to transmit radio waves.