Dielectric Characterization at Millimeter Waves With Hybrid Microstrip-Line Method

This paper proposes a hybrid microstrip-line method for characterizing materials with unknown dielectric properties at millimeter-wave (mm-Wave) frequencies. The proposed method introduces two error boxes, representing the impedance mismatch and discontinuities caused by signal path transitions between two different types of transmission lines. Therefore, unlike conventional covered- or two-transmission-line methods, the proposed method requires neither a perfect impedance match between the test fixture and the coaxial cables nor a high reproducibility of the transitions' radio frequency characteristics. We applied the proposed method to characterize two types of dielectric materials: Rogers RT/d5880 standard high-frequency substrate and a plain-woven polyester fabric substrate, using a single setup with an in-house designed universal test fixture in the 37-39 GHz range. The accuracy of the proposed method under imperfect fixture conditions is demonstrated.