Abstract: In this paper the measurement of complex permittivity of substrate of microwave printed circuit board are investigated. Vector network analyzer (VNA) is used, and strip lines matched with coaxial line port are used as the structure to be measure. The information of complex permittivity of the strip line is included in the characteristic impendence and complex propagation constant of the strip line, which can be obtained from ABCD matrix. S parameters of the strip line can be measured by VNA, and they can be transformed into ABCD matrix, then the complex permittivity of the substrate can be obtained. To get correct results, the measurement system have to be calibrated. Here a calibration method result from TRL calibration principle is used.

Key words: Permittivity, Loss tangent, ⁺Strip line, TRL calibration technique