On the dielectric properties of substrates with different surface conditions for submillimeter-wave and terahertz applications

Dielectric constant and loss tangent are essential material parameters in designing and predicting the performance of submillimeter-wave and terahertz devices. In this paper we investigate dielectric properties of substrate materials using pulsed time-domain spectroscopy. It is found that these dielectric properties depend on the preparation process of the sample under test as different process results in different surface condition. Two different substrates, namely, printed-circuit board laminate and 3D printing polymer, with different preparation methods are used to illustrate the impact of surface condition of the sample to the extracted dielectric properties. A Fresnel zone-plate lens with a circular grating reflecting plane operating at 0.3 THz is designed and measured. Good agreement between simulation and measurement results is achieved when proper dielectric properties and surface model are employed.