Broadband Complex Permittivity Measurements Using Multimode Split-Rectangular Waveguide Resonator

This paper discusses a method for measuring the complex permittivity of the dielectric substrates, over a wide band from microwave to millimeter-wave frequencies using a split-rectangular waveguide resonator. In this resonator, a waveguide short-circuited at both ends is split in the center along the E-plane, and the test substrate is inserted in the split plane with a spacer. The relative permittivity
$\varepsilon_{rt}$
and dielectric loss tangent
$\boldsymbol{\tan\delta_{t}}$
in the tangential direction of the dielectric substrates are extracted from the resonant frequency and unloaded Q-factor of the
$\mathbf{TE}_{10p}$
resonant mode. The frequency dependence of
$\varepsilon_{rt}$
and
$\boldsymbol{\tan\delta_{t}}$
for three different dielectric substrates at 20–60 GHz was evaluated using the split-rectangular waveguide resonator to demonstrate an effectiveness of this method.