Cost-Effective 3-D-Printable Image Dielectric Guides Based 3-dB Coupler for Millimeter-Wave Applications

Low-cost 3-D-printing techniques are proposed to fabricate image-dielectric guides (IDGs) for millimeter-wave (mm-wave) applications in the Ka band. The 3-D-printed IDG is fabricated by the stereolithography (SLA) process using a polymer resin. An open-ended coaxial probe technique has been employed to characterize the electrical properties of the 3-D material from 26 to 40 GHz. The conventional IDG design is modified by introducing a thinner dielectric layer between the dielectric guides (DGs) and the ground plane. This layer improves the fabrication and measurement accuracy without affecting the IDG performance. Furthermore, the two-line transmission lines technique is used to characterize the propagation constant. The measurement shows an insertion loss of 0.025 dB/mm. Taking advantage of the low-cost and low-loss attributes of IDGs, a 3-dB IDG-based coupler has been designed. The proposed techniques allow the customization of the IDG-coupler for different coupling levels just by varying the slot width and rotation. Due to structure simplicity, the proposed coupler prototypes are fabricated using just copper tape and a 3-D printer. The 3-dB coupler reveals a bandwidth of 5 GHz with ±0.7 dB of power equality and 20 dB of isolation. The simplest structure, high isolation and matching, control over coupling ratio, and much lower fabrication cost emphasize the use of the proposed coupler in mm-wave applications.