Generating Tunable Orbital Angular Momentum Radio Beams With Dual-Circular-Polarization and Dual-Mode Characteristics

In this paper, a mode and circular-polarization (CP) simultaneously reconfigurable patch array antenna for orbital angular momentum (OAM) beams generation is presented and experimentally investigated. The array antenna simply consists of a 1:4 power divider and four antenna elements, each of which is fed with two switchable ports and a quadrature phase shift. Besides, the four elements are arranged using an orthogonal configuration. In this manner, switchable CPs are generated for each element, and switchable ±90° phase differences are obtained between adjacent elements. By strategically varying the ON/OFF status of the p-i-n diodes loaded as switches, the antenna could operate among left-hand CP (LHCP) with OAM-mode +1 or −1 and right-hand CP (RHCP) with OAM-mode +1 or −1. Without additional phase-shifting networks, the design method can be easily extended to large-scale antenna arrays. According to the measured results, an overlapped operational band of 2.39 to 2.64 GHz is obtained among the four states. In addition, both far-field and near-field distributions are performed to verify the design. Owing to its flexibility of OAM mode and polarization reconfigurablity as well as symmetrical and simple configuration, the antenna could be a promising application in future OAM-based communications system.