Very compact 3D-printed folded branch-line hybrid coupler based on loaded helical-microstrip transmission lines

Abstract

This paper presents a 3D topology for high miniaturization of the well-known hybrid branch-line coupler at the UHF band. A preliminary work already proposed the use of helical-microstrip TLs combined with a folded structure for this purpose. This extended work includes a compactness enhancement by loading the TL segments with capacitors. An study of loaded helical-microstrip TL is reported as well. The coupler prototypes have been simulated and fabricated by using a combination of Additive Manufacturing and copper electroplating. The performance results have been compared to the conventional model showing a good agreement. In order to place the designed devices within the state of the art a figure of merit that combines the compactness and the relative bandwidth has been proposed, showing very good results in terms of miniaturization.