A 0.38–67-GHz Directional Coupler With GSG Interface for Compact VNA System

This letter introduces an ultrawideband directional coupler with ground-signal-ground (GSG) interfaces that can be seamlessly integrated with the monolithic microwave integrated circuit (MMIC) mixers within a compact 67-GHz vector network analyzer (VNA) system. The coupler is fabricated through metal copper additive manufacturing process. To mitigate the impact of the polymer strips on the coupler’s raw directivity, the coupled lines were designed with a special impedance function, which effectively increases the average spacing between them, so the parasitic couplings from the polymer can be reduced. Additionally, enhancements to the polymer fabrication process now allow for the supporting strips to be meshed, further enhancing the directivity of the coupler. The fabricated coupler shows good performance in the operating frequency of 0.38–67 GHz, and the simulation results are in good agreement with the measured results: coupling of $13.5~\pm ~0.17$ dB, insertion loss <3>13 dB, and directivity of >12 dB (>15 dB at 1.72–67 GHz).