Design of Fabrication Error-Tolerant Microstrip Directional Coupler

In this paper, an error tolerance design technique is proposed and demonstrated by 28GHz microstrip directional coupler. By including the tolerance requirement of PCB fabrication errors as one of the objective functions, multi-objective optimization searching for the optimal fragment-type structure of the directional coupler can be implemented to acquire both high performance indices and high error tolerance. Design and test of 10-dB directional coupler operating at 28 GHz band on PCB of area of 2.54mm×5.76mm indicates that return loss of 24dB, directivity over 25dB in an operation bandwidth of approximately 22% can be acquired. In addition, the coupler has almost the same fabrication error tolerance as the microstrip coupler operating at the 2 GHz band.