Rotman Lens-Fed Antenna for Generating Multiple Orbital Angular Momentum (OAM) Modes With Gain Enhancement

A compact multi-layer Rotman lens-fed array antenna which can generate nine orbital angular momentum (OAM) modes is presented in this paper. The proposed antenna consists of a microstrip Rotman lens and a nine-element circular array antenna which utilizes high-gain patch element in order to enhance the gain of OAM beam. A stacked patch loaded with two slots is attached above the patch element to effectively enhance the antenna gains. By employing the Rotman lens as the feed network of the circular array, nine OAM-carrying beams of modes number ℓ =0 , ±1, ±2, ±3 and ±4 can be produced when different input ports are excited, respectively. 160°-phase-shift on adjacent output ports can be achieved to meet the phase requirement of OAM modes of ℓ = ±4. Moreover, the Rotman lens is modified by adjusting the deflection angle of the beam ports and array ports so as to achieve uniform amplitude distribution on the output ports. Hence, the pattern characteristics of OAM beams can be effectively improved by making all the output ports are equal in amplitude. The C-band prototype of the antenna is fabricated and measured. Both the simulation and measurement results indicate that nine OAM modes can be generated by using the proposed structure. The proposed antenna can be used in an OAM-based wireless communication system.