3-D Compact 3-dB Branch-Line Directional Couplers Based on Through-Silicon Via Technology for Millimeter-Wave Applications

A bandwidth optimization model for a novel equivalent 90° transmission-line section is proposed in this paper. Furthermore, the structure of 3-D compact 3-dB branch-line directional coupler and its equivalent-circuit model are presented. They can achieve both excellent isolations between each branch and high-density integration by using equivalent 90° transmission-line sections and coaxial through-silicon via technology in 3-D integrated circuits. Finally, a 3-D coupler is designed with the center frequency of 100 GHz, as well as the bandwidth and size reach 20 GHz and 174 × 236.9 × 208.7 μm
³
, respectively. The results of the 3-D full-wave field solver High-Frequency Structure Simulator and the proposed model are well matched, showing that the proposed model can be used to quickly evaluate the electrical performance of the 3-D coupler before manufacture, thus effectively promoting the design efficiency and quality.