Microstrip Transmission Line Method for Broadband Permittivity Measurement of Dielectric Substrates

This paper presents a novel microstrip transmission line method for broadband relative permittivity measurement of planar dielectric substrate materials. The method requires three sets of S-parameter measurements of the microstrip line together with an obstacle in three equidistant positions over the line. The measurement and simulation results for the broadband relative permittivity of high-frequency substrates, TLX-8, RF60A, CER10, and the widely used FR4 are presented. The errors are calculated based on the manufacturers' data sheet value. Both the simulation and measurement results are found to be within 16% of the data sheet values for CER10 and 10% for all other substrates. The proposed method can minimize errors due to the nonreproducibility of connectors and impedance mismatch problems, prevalent in transmission line methods. However, the method is highly sensitive to the positioning of the obstacle, which can be overcome through the use of high accuracy obstacle positioning methods.