A Miniaturized Wideband 4×8 Butler Matrix for Beamforming in Millimeter-Wave Applications

This article presents our study on a wideband miniaturized
$4\times8$
Butler matrix (BM) beamforming network based on a stacked metallic waveguide layout in millimeter-wave band. The size and complexity of the
$4\times8$
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
$H$
-plane and
$E$
-plane and a broadband 45° phase shifter realized by loading inductive and capacitive irises in both paths, the operating bandwidth of the proposed
$4\times8$
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
$S_{11}< -15$
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
$4\times8$
BM, the bandwidth is increased by threefold and the size is reduced by more than 50%.