The most widely used class of antenna, a dipole antenna consists of two symmetrical radiators such as metal rods or wires, with one side of the balanced feedline from the transmitter or receiver attached to each. A horizontal dipole radiates in two lobes perpendicular to the antenna's axis. A half-wave dipole the most common type, has two collinear elements each a quarter wavelength long and a gain of 2.15 dBi. Used individually as low gain antennas, dipoles are also used as driven elements in many more complicated higher gain types of antennas.

Question: What is the most widley used antenna class?
Answer: dipole antenna

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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   What radiates two lobes perpendicular to the antennas axis?                                                                                                                                       
Answer: horizontal dipole

Question: Besides low gain antennas, what is also used as driven elements in complicated higher gain types of antennas?
Answer: dipoles

Question: How much gain does a half-wave dipole have?
Answer: 2.15 dBi