A Miniaturized Wideband 4×8 Butler Matrix for Beamforming in Millimeter-Wave Applications
Wen Sun, Xin Rao, Guodong Su, Lingling Sun, Chao Shu, Xiaodong Chen
Abstract
This article presents our study on a wideband miniaturized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times8$ </tex-math></inline-formula> Butler matrix (BM) beamforming network based on a stacked metallic waveguide layout in millimeter-wave band. The size and complexity of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times8$ </tex-math></inline-formula> BM have been substantially reduced by introducing a double-layer structure to avoid eight cross-overs and by using reverse feeding to eliminate four band limiting 180° phase shifters. Additionally, by introducing two kinds of wideband hybrid couplers in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -plane and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -plane and a broadband 45° phase shifter realized by loading inductive and capacitive irises in both paths, the operating bandwidth of the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times8$ </tex-math></inline-formula> BM has been substantially increased. Furthermore, a Chebyshev amplitude distribution among the eight outputs has been realized through the unequal power dividers to suppress the sidelobes. The beamforming network and magnetoelectric (ME)-dipole array have been verified in the experiment, showing an operating bandwidth of 60–80 GHz with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}< -15$ </tex-math></inline-formula> dB. The sidelobe of the radiation pattern is below −14 dB at 70 GHz and the peak gain is 18 dBi in the operating band. The beam switching angles are ±11° and ±35° for each port, respectively. Compared with the reported similar work on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times8$ </tex-math></inline-formula> BM, the bandwidth is increased by threefold and the size is reduced by more than 50%.