Application of 3-D Printing Technology for the Realization of High-Performance Directional Couplers in Suspended Stripline Technique

In this paper, a novel approach for the realization of high-performance coupled-line directional couplers in suspended stripline technique is proposed, taking advantage of the recent development in 3-D printing technology. An enhanced 2.5-D dielectric structure is introduced, allowing to combine the advantages of strip transmission line techniques, for which the circuit can still be considered as a quasi-planar structure, with the 3-D printing flexibility allowing to realize locally variable air layer thicknesses limited only by technological constraints. It is shown that the proposed approach is especially useful when tight coupling, as for which thick air layer in the coupled-line region is required and compact structure is of need. Moreover, compensating elements, often required to improve couplers' performance, can easily be realized as a combination of a circuit mosaic and varied ground plane for better circuit volume utilization. An example of a 3-dB coupled-line directional coupler operating within the ISM 5.8-GHz band is designed, manufactured, and measured for the experimental verification. The obtained results confirm the applicability of the proposed approach.