Multiobjective Optimization Design of High‐Directivity Microstrip Tight‐Coupling Directional Coupler With Node‐Segment‐Type Structure

ABSTRACT In this paper, a novel technique for the design of microstrip tight‐coupling directional coupler with node‐segment‐type structure (NSTS) is proposed. The NSTS is configured by connecting microstrip line segments among free nodes distributed on the print circuit board (PCB). L‐shaped line segments characterized by constraint nodes and individual width are proposed for detailed geometry description of NSTS. The optimal NSTS can be acquired by implementing multiobjective optimization search for the optimal distribution of the nodes and the line widths. For demonstration, a 3‐dB microstrip directional coupler working at 1.75 GHz is designed with NSTS in a compact size. The measurement indicates that high directivity over 36 dB and amplitude imbalance of < ±1 dB in an operation bandwidth of 33% can be obtained.