Transmission Line Loss Properties of Dielectric Loss Tangent and Conductive Surface Roughness in 5G Millimeter Wave Band

Loss properties of three types of transmission lines—microstrip line (MSL), stripline (SL), and substrate-integrated waveguide (SIW)—were investigated. Specifically, the dielectric loss tangent (Df) and the conductive surface roughness (Rq) in the 5G millimeter wave band were studied for the purpose of base material development and base material selection. Results of Df and Rq for each transmission line type were obtained from electromagnetic simulations. We show that for the SL and SIW, the conductor loss dominates when the substrate is thin, the thickness being of order 100 $\mu$m. In reducing this loss, a copper foil of low roughness is effective. The loss properties of the MSL and SIW were evaluated up to frequencies of 100 GHz and at 28 GHz, respectively. Both the calculated and measured losses were found to be in good agreement.