Dual-Band Permittivity Measurement of Thin Dielectric Layers with a Simple Planar Device

An improvement of a method for permittivity measurement is introduced based on a dual-band four port planar structure, consisting of two cascaded cross-coupled quadrature hybrids connected through two transmission lines. The applicability of the method to permittivity measurement of thin dielectrics is then demonstrated: permittivities are evaluated at two different frequencies f0 and n*f0 (n=1,2,3..) by simply detecting the two output amplitudes, thus avoiding any phase measurement and allowing a remarkable space reduction. A prototype has been fabricated in microstrip technology and experimentally tested exhibiting very good accuracy for permittivity measurement at two different frequencies spaced by an octave band.