Conductor surface-roughness effect in the loss tangent measurement of low-loss organic substrates from 30 GHz to 70 GHz

This work shows the effect of the conductor surface roughness (CSR) in the measurement of the loss tangent using the microstrip ring resonator method (RRM) in three low-loss, organic dielectric substrates (RT/duroid 6002, 6202 and 5880) and each, with two types of copper metallization. In addition, relative permittivity and loss tangent measurements are presented from 30 GHz to 70 GHz for the three substrates for the first time using the RRM. The copper metallization types used for the study are the rolled metallization with a root mean square (RMS) CSR value of 0.27 um and the Electro-deposited (ED), with an RMS CSR of 1.89 um. Results show that the extracted loss tangent values from the ED metallization are in excellent agreement with the values extracted with a Split Cylinder Cavity at about 34 GHz for all materials studied. On the other hand, the loss tangent values extracted with ring resonators fabricated on a rolled metallization, show errors of about 50%, when compared to those extracted with the same Split-Cylinder cavity. No significant errors were detected in the extracted relative permittivity with the two CSR values, and errors below 6% were achieved when compared to the values extracted with the Split Cylinder method.