Design Of A Small Size 8 × 8 Butler Matrix In C-Band

This paper presents the design of 4 × 4 and 8 × 8 Butler matrices in C band at 5.8 GHz center frequency. These matrices have been designed in C band with the intention of using them in avalanche detection system in future. The topology used for designing the Butler matrices has dimensions much smaller as compared to the conventional topology and it is easy to design and fabricate as well. However, being designed at a higher frequency, the input and output ports are so close to each other that placement of connectors becomes very challenging. This paper also addresses this issue wherein, the entire network has been redesigned and rigorously optimized so that the connections can be made easily and obtained results are not disturbed much as well. The network has been designed on Rogers RT5880 (Lossy) substrate. The performance of the fabricated 4 × 4 Butler matrix has been evaluated. The experimental results shows that transmission coefficients obtained are approximately 6.7 dB across the output ports with a maximum amplitude imbalance of 0.5 dB. Isolation and Return loss obtained are below -17dB and -21 dB respectively. Maximum insertion loss obtained is 0.8 dB, whereas average insertion loss is 0.65 dB. Phase shifts at the output ports achieved are satisfactory as well. Once the 4 × 4 Butler matrix was designed successfully with desired results, it has been used for the designing of 8 × 8 Butler matrix. The simulation results obtained for 8 × 8 Butler matrix are satisfactory. The transmission coefficients obtained are approximately -10 dB with maximum amplitude imbalance of 0.7 dB. The isolation between the ports and return loss obtained are better than -16.5 dB and -17 dB. Phase shifts obtained are also satisfactory.