In a directional antenna in which the objective is to emit the radio waves in one particular direction, the antenna is designed to radiate most of its power in the lobe directed in the desired direction. Therefore in the radiation plot this lobe appears larger than the others; it is called the ""main lobe"". The axis of maximum radiation, passing through the center of the main lobe, is called the ""beam axis"" or "boresight axis"". In some antennas, such as split-beam antennas, there may exist more than one major lobe. The other lobes beside the main lobe, representing unwanted radiation in other directions, are called minor lobes. The minor lobes oriented at an angle to the main lobe are called ""side lobes"". The minor lobe in the opposite direction (180°) from the main lobe is called the ""back lobe"".