Substrate characterization: simulation and measurement at high microwave frequencies

In this paper we present new measured loss tangent data for commercially available substrates, and these data are supported by simulations that show how practical variations in loss tangent affect the performance of microwave interconnections and devices. The paper reviews the measurement techniques that are currently available to measure the dielectric constant and loss tangent of substrate materials, and includes a new variation on an existing method that enables substrate parameters to be more easily measured but retains high accuracy. Simulations have been performed on microstrip lines fabricated on 10mil thick substrates using gold conductors to show the relative contributions of conductor and dielectric loss to the total line loss over the frequency range 0‐40GHz. Included in these simulations are the effects of conductor surface roughness. The simulated data are related to measured line microstrip line loss data over the frequency range 50MHz‐40GHz. The measured values, for an etched gold line on alumina, vary from 0.0045dB/mm at 50MHz to 0.04dB/mm at 40GHz.