A novel broadband electronically beam scanning structure based on Luneburg lens phased array is investigated in this paper. The radiation elements of the phased array are mounted on the surface of a Luneburg lens. Without amplitude and phase control of the elements, only discrete scanning angles are available. In this paper, beam scanning to arbitrary angle is demonstrated by fully controlling the amplitude and phase. Compare to conventional phased array beam scanning system, the proposed structure has no scan angle coverage limit and has a broadband working frequency. Also, due to the symmetry of Luneburg lens, no beam shape variation would occur during angle scanning. Moreover, this structure requires much less system complexity to achieve a highly directional beam and therefore the cost of this system could be much lower than conventional phased array.