A 4 × 4 Millimeterwave-Frequency Butler Matrix in Grounded Co-Planar Waveguide Technology for Compact Integration With 5G Antenna Arrays
Laura Van Messem, Arno Moerman, Olivier Caytan, Igor Lima de Paula, Bram Hoflack, Bram Stroobandt, Sam Lemey, Marc Moeneclaey, Hendrik Rogier
Abstract
This article presents a novel <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> Butler matrix implemented in the grounded co-planar waveguide (GCPW) technology, compactly integrated with a highly efficient and broadband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> air-filled substrate integrated waveguide (AFSIW) cavity-backed patch antenna array (AA), giving rise to a broad operational frequency range [23.75, 31 GHz] (26.5%) covering the n257, n258, and n261 fifth-generation (5G) bands. Three novel quadrature hybrid couplers and two crossovers are designed and compared to obtain the optimal building blocks for the Butler matrix. Within each of the supported 5G bands, the measured excess insertion loss of the optimized Butler matrix remains smaller than 3.5dB with a maximal amplitude imbalance of ±0.9dB. Isolation between input ports is higher than 16.4dB. A maximal measured realized gain of 12.3dBi is obtained for the Butler matrix with integrated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> AA while ensuring a −3-dB beamwidth coverage of 110°. The main beamsteering directions of [−40°, −14°, 14°, 40°] exhibit measured deviations that stay within ±3°. The fabricated Butler matrix with AA features a very compact footprint of 21.4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> 46.0 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 mm [ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\lambda _{0} \times 4.3\lambda _{0} \times 0.2\lambda _{0}$ </tex-math></inline-formula> ].