Design of Planar 8-by-16 Butler Matrix for 16-Element Switch-Beam Antenna Array

In this paper, a planar 8x16 Butler matrix is designed using microstrip technology to build up a 16-element switched-beam antenna array. By connecting 180 degrees hybrid couplers with 8 output ports of the conventional 8x8 Butler matrix, each original output is split into two ports with an equal power division and a 180 degrees phase difference. Hence, the outputs of the Butler matrix can be expanded to 16 outputs. As the developed matrix is integrated with 16 microstrip antenna elements, one can form a 16-element switch-beam antenna array with 8 switched beams pointing to 8 different azimuth angles. The measured radiation patterns of the developed antenna array demonstrate that the main-beam directions point to azimuth angles of -47 degrees, -33 degrees, -19 degrees, -4 degrees, 5 degrees, 17 degrees, 30 degrees, and 46 degrees at 9.4 GHz and agree the theoretical results very well.