Thickness-Independent Reference-Plane-Invariant Noniterative Permittivity Extraction of Low-Loss Solid Dielectric Samples by Combined Use of Frequency- and Time-Domain Analyses

A novel noniterative microwave method is proposed for relative permittivity
$\varepsilon _{r}$
extraction of solid samples using thickness-independent reference-plane-invariant (RPI) expressions. The main idea behind our method is the usage of the frequency-domain first reflection coefficient (in addition to full scattering parameters) obtained from gating the first peak inside the sample using a proper time-gating procedure. To validate and examine its accuracy, measurements of
$\varepsilon _{r}$
have been performed over 0.01–26.5 GHz for three different dielectric materials [acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol (PETG), and the polylactic acid (PLA)] with different thicknesses positioned into a 50-
$\Omega $
coaxial airline. The effects of a number of frequency points, the value of IF bandwidth (BW), the window type, and the span of the window on
$\varepsilon _{r}$
by our method are examined.