This paper proposes a broadband omnidirectional circularly polarized (CP) antenna based on a loop-dipole configuration.The antenna consists of four pairs of titled dipoles and a broadband feeding network.The four pairs of titled dipoles are wrapped around a cylinder.Each pair of titled dipoles includes a driven dipole and a parasitic element which is introduced to enhance the bandwidth.The feeding network is composed of four broadband baluns and an impedance matching circuit.Experimental results show that this CP antenna has a 15-dB return loss bandwidth of 31%(1.68-2.31GHz) and a 3-dB axial ratio bandwidth of 30%(1.7-2.3GHz).The gain variation in the horizontal plane is less than 1dB