Detailed Analysis of Multilayer Broad-Side Coupler with a Symmetric Structure

Abstract

A detailed analysis of a multilayer symmetric coupler employing symmetrical broad-side coupled lines is presented. We confirm that the coupler can be designed using a well-known even-odd mode analysis of two strip lines while the coupler has four strip lines. We also confirm that the previously reported poor isolation originates from port mismatching. To verify the analysis, couplers that have different dimensions are fabricated. One example exhibits a coupling loss of 4.5±0.5dB, a return loss better than 15dB, and isolation characteristics higher than 12dB in the 6.5 to 15.1GHz frequency range. These results agree well with the obtained simulation results. The results show that the coupler has the potential to provide tight and ideal coupling.