Development of Crossover-Free 8 × 8 Butler Matrix for 2.4 GHz Beamsteering Applications

In this paper, a crossover-free $8 \times 8$ Butler matrix is developed for 2.4 GHz beamsteering applications. The design aims to address the limitations of conventional $8 \times 8$ Butler matrices, which suffer from significant insertion losses and large physical dimensions due to the excessive use of crossovers. By eliminating crossovers, the proposed $8 \times 8$ Butler matrix achieves a more compact design with improved phase alignment and reduced insertion loss. The design is deployed on an FR4 Epoxy substrate with the dielectric constant of 4.3 and the thickness of 0.8 mm. The total size of crossover-free $8 \times 8$ Butler matrix takes 178.6 mm by 137.8 mm, representing a 55.4% size reduction compared to the conventional one. The results show that the reflection coefficients for all inputs and isolated ports are under $-\mathbf{2 0 ~ d B}$, and the insertion loss at the output port ranges between -10 dB and -11 dB, nearing the theoretical prediction of 9 dB. Furthermore, the proposed $8 \times 8$ Butler matrix achieves the fractional bandwidth of 13.75% at Port 1 and 25.4% at Port 4, indicating its wideband characteristics. In addition, the design of crossover-free $8 \times 8$ Butler matrix offers significant size reduction and improved performances, making it suitable for compact beamsteering antenna array applications.