Designs of deformed eight-way Butler matrix with port reduction for massive array beamforming

Massive-MIMO technology has been proposed for 5G systems, in which beamforming is one of the essential features. In this work, folding deformation technique is proposed to reduce the size of the Butler matrix (BM) used in array system. Based on the mirror symmetry of the conventional BMs, partial components can be saved. By embedding some switches from the feeding network into the internal BMs, the number of building blocks and input ports is decreased. For demonstration, both 4 x 8 BMs and 2 x 8 BMs deformed from a conventional 8 x 8 BM are designed and implemented in this work. Up to 25% reduction in size is achieved when compared to a conventional 8 x 8 BM. The proposed BMs not only can generate eight orthogonal beams, but also can perform the beam synthesis, showing a great potential for future communication systems.