Computing the Relative Permittivity and Loss Tangent of Sub-strates by the Numerical Model of a Microstrip Transmission Line

Abstract

The microstrip transmission line numerical model is used to search out the relative permittivity and loss tangent of the materials of the substrate at the high-frequency range (400 MHz – 3GHz). This thesis shows outcomes of the transmission line numerical model in simulation software ADS and those of practical implementation. The microstrip transmission line was measured by vector network analyzer. There are multiple substrate materials employed namely, FR4, AR1000, EPDM cell rubber foam, wood, wood wet. The substrate material FR4 and AR1000 play as reference material to examine the efficiency of the numerical model. The wood wet was used to check the increase of the relative permittivity and loss tangent when the moisture in the substrate levels up. Additionally, the surface roughness measurement data is also added to the model in order to make the model as similar to the real device under test as possible. The dimension and size of the microstrip lines in the model are identical to the practical line to reduce the mismatch of the outcomes.

The choosing results of the relative permittivity and loss tangent based on the maximum attainable power gain comparison between the model and practical measurement results. The best data is selected based on the least squares method estimation. In order to assess the accuracy of the found relative permittivity and loss tangent, the low pass filter and passive UHF RFID antenna are employed. The comparison between the model and measurement results of these devices are used.

In this thesis, fundamental knowledge related to microstrip transmission lines and the least squares method will be taken into account. Finally, the future works to improve the transmission line model will be discussed in the conclusion part.