Design of High-Directivity Directional Couplers With 2-bit Fragment-type Structure

In this paper, a novel 2-bit scheme based on fragment-type structure on the microstrip line is presented. The 2-bit scheme is adding two new states in one cell on the basis of the traditional 1-bit scheme by introducing gap and thin line inside the cell. Without manual preset and optimization of parameters, suitable structure will be automatically searched combined with the multi-objective optimization algorithm MOEA/D-GO. For demonstration, two 2-bit wideband directional couplers at 2 GHz with the coupling of 10-dB and 20-dB are designed. They both provide excellent directivity, with maximum performance directivity of 65 dB and 49 dB, respectively. Compared with the traditional 1-bit fragmentation structure, the number of iterations achieving the same design objections is less without preset.