Circuit Analysis of a Coplanar Waveguide (CPW) Terminated With a Step-Impedance Resonator (SIR) for Highly Sensitive One-Port Permittivity Sensing

This paper presents a single-frequency reflective-mode phase-variation microwave sensor devoted to the dielectric characterization of materials. The device is implemented in coplanar waveguide (CPW) technology and consists two parts: (i) sensing region, step-impedance resonator (SIR) as termination CPW transmission line, (ii) design cascade high/low impedance quarter-wavelength inverters, used boost up sensitivity. By placing so-called material under test (MUT) on top capacitance SIR altered due effects constant MUT. modifies phase reflection coefficient seen from input port, output variable. From circuit analysis, it demonstrated that sensitivity for small perturbations vicinity reference (REF) can be optimized by setting operation frequency resonance loaded with such REF material. maximum one reported sensors high 66.5°, main figure merit, defined ratio between area region expressed terms squared guided wavelength, FoM = 3643°/λ2. Such merit represents significant improvement compared equivalent means an open-ended line. equivalence semi-lumped element (i.e., SIR-based) fully distributed counterpart also analyzed paper.