A Dimension-Reduction Multibeam Antenna Scheme With Dual Integrated Butler Matrix Networks for Low-Complex Massive MIMO Systems

In this letter, a multiple-beam antenna (MBA) scheme with reduced port dimension is proposed for low-complex massive multiple-input-multiple-output (MIMO) systems. From practical scenario consideration, two 2-port and 8-element subarrays with dual 2-to-8 Butler matrix networks are designed for 3 dB beam coverage within 60° sector. Based on channel capacity analysis of an 8-subarray (8 × 8-element) antenna system, it is proved that only 25% number of radio frequency (RF) chains are utilized in the proposed scheme to achieve a competitive data transmission rate, compared with a regular 8 × 8-element and 64-chain massive MIMO system, with the advantages of low cost, low system weight, and low complexity of signal processing. The proposed 8-subarray system is built and measured to verify the antenna performance. The proposed multibeam antenna scheme exhibits potential possibilities in low-complex and low-cost massive MIMO systems for the fifth-generation (5G) applications.