A Novel Spatial Three-dimensional Spherical Array Antenna for OAM Waves Generation

Further demands on data transmission bring new challenges for the capability of wireless network due to the rapid developments of wireless communication technology. Since different orbital angular momentum (OAM) modes are orthogonal to each other and multiple signals can be transmitted at the same frequency, OAM multiplexing technology is an effective method to increase the capacity of wireless channel, which has attracted much attention in recent years. The investigations on generation of OAM waves is significant for the application and advance of OAM multiplexing technology.In this paper, a new three-dimensional configuration of array antenna is presented to generate vortex electromagnetic waves carrying orbital angular momentum. The proposed spherical array antenna (SAA), which is made up with M layers uniform circular array antenna (UCA) and each UCA contains N antenna elements, is a spatial expansion based on UCA and all antenna elements are distributed on a spherical surface of the same radius. Different OAM modes are obtained by changing the phase distribution of antenna elements when the amplitudes are uniformly distributed. To demonstrate the feasibility of the array design, the theoretical analysis of the far-field and vector potential expressions are elaborately deduced. Besides, two spherical array antennas with different structures are simulated and the simulation results demonstrate that different OAM modes can be generated, which further verify the theoretical discussion. This new array pattern performs better in radiation directivity compared with the conventional UCA, so that the beam is more concentrated and beneficial to long-distance transmission and reception for the vortex electromagnetic waves.