Design and Implementation of Nonuniform Broadband 3 dB Tandem Directional Coupler

In this paper, a high-performance nonuniform broadband 3 dB tandem directional coupler based on multilayer process is proposed. In the process of design synthesis, the least square method is used to iteratively solve the weight factors, and this new approach provides flatter coupling response to the design rather than relying on design tables. To verify the rationality of the improved synthesis process, a nonuniform tandem coupler operating at 1-10 GHz was designed. The result shows that the design has good performance over a relative bandwidth of 163.6%, which is promising for broadband applications.