The design of Substrate Integrated Coaxial Line (SICL) based wideband baluns for K-band application are presented in this work. The proposed two-section branch-line balun realized in SICL technology can be fabricated using traditional PCB technology. The performance of the planar and folded balun are evaluated to demonstrate low amplitude and phase imbalance in the entire K-band covering 18 GHz to 26 GHz. Fractional bandwidth of 40.68% and 37.27% are achieved by the proposed planar and folded balun, respectively. The size of planar SICL balun is 0.73λg × 0.78λg × 0.05λg, and the folded balun covers only 58% lateral area as compared to the planar balun. The wide-band single mode TEM characteristics of these baluns realized in SICL technology have enhanced shielding capability which motivates their usage in densely integrated millimeter-wave systems. © 2018 IEEE.