Miniaturized SIW Multibeam Antenna Array Fed by Dual-Layer 8 × 8 Butler Matrix

This letter presents a multibeam antenna array fed by a substrate integrated waveguide 8 × 8 dual-layer Butler matrix within the band from 28 to 31 GHz. The dual-layer structure is adopted aiming to achieve miniature, so that the size of the structure is reduced by more than 50% compared with similar single-layer design. The utilization of dual-layer structure also decreases the complexity of the whole Butler matrix. A 2 × 8 slot antenna array is used as the radiating portion to obtain high gains and relatively low side lobe levels. The proposed multibeam antenna array is fabricated and tested to verify the performances.