Design of Wideband 16 × 16 3-D Butler Matrix for Multimode OAM Generation

Vortex electromagnetic waves carry different orbital angular momentum (OAM) modes that are orthogonal to each other. The reuse of these OAM modes can greatly improve channel capacity. To satisfy the need for high-order mode and multimode OAM, a novel topology calculate method and 3-D connect technology is introduced in OAM generate type <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times 16$</tex-math> </inline-formula> Butler matrix (BM) for the first time in this article. The BM provides the phase distribution of −7- to +7-mode OAM with a simplified connection and high integration through a 3-D design. The BM is connected to a 16-element uniform circular antenna array (UCA) to generate −7- to +7-mode vortex waves in the S-band. In addition, the BM and UCA achieve a 33% relative bandwidth, further improving the communication rate. To verify the proposed design method, the BM and UCA were fabricated and measured. The results indicate that the amplitude and phase imbalance of the designed BM are below 1.2 dB and 15°, respectively, for all OAM modes in the 5–7 GHz. The generation of −7- to +7-mode OAM is observed using near-field and far-field measurements. The results demonstrate that high-order and multimode OAM can be achieved for multiplexing. The proposed BM and OAM antennas hold great potential for various applications, such as enhancing channel capacity and improving MIMO system in 6G communication.