This disclosure provides an antenna, an antenna system, and a vehicle, and pertains to the field of wireless communication technologies. The antenna includes a main antenna, a parasitic antenna, and a mainboard, where the main antenna and the parasitic antenna are both located on a surface of the mainboard, and a plane on which the main antenna is located and a plane on which the parasitic antenna is located are parallel, and are opposite to each other. A feeding point of the main antenna is connected to a feeding transmission line of the mainboard, and the parasitic antenna is connected to a second ground end of the mainboard. A difference between a resonance frequency point of the main antenna and a resonance frequency point of the parasitic antenna is less than a target threshold.