Staircase Array Antenna With Stacked Butler Matrix for Concurrent Multi-Beams

Massive Multiple-Input Multiple-Output (Massive MIMO), which uses a large number of antenna, has been investigated to realize high-speed wireless communications. However, as the number of antenna increases, the number of components also increases. In addition, it has the problem that circuit mounting becomes difficult due to the narrow antenna spacing and increased loss and phase deviation. To solve these problems, this paper proposes a compact configuration for concurrent multi-beams. The proposed antenna is composed of a one-dimensional patch array antenna and a Butler matrix, which are stacked on top of each other in a staircase configuration. The proposed antenna is fabricated by stacking several identical substrates, reducing design and manufacturing costs. Fixed beam steering can be realized depending on the input port of the Butler matrix. In addition, the phase shifter can steer beams in the direction orthogonal to beam steering by the Butler matrix. To verify the design results, the prototype antenna, an $8 \times 8$ patch array antenna consisting of eight substrates, is fabricated at 28 GHz. Beam steering was achieved in the range of −55° to 55° by inputting the outputs to the respective ports of the Butler matrix and in the range of −29° to 25° by phase shifter