Permittivity Estimation of Dielectric Substrate Materials via Enhanced SIW Sensor

An enhanced substrate integrated waveguide (SIW) cavity sensor is proposed and designed in this work operating under sub -6 GHz 5G band suitable for the accurate permittivity estimation of low-loss dielectric materials. The proposed SIW sensor is designed for the fundamental TE
₁₀₁
mode at the resonance frequency of 3 GHz. The designed sensor is excited by employing a newly optimized external coupling topology incorporating a transition offset, contrary to the conventional microstrip feed. Due to which, a fully planar SIW sensor is developed for the first time without incorporating any active component, exhibiting a substantially high unloaded quality factor of nearly 515 basically required for the accurate testing of low loss tangents. Besides, the designed sensor is yielding a high sensitivity of 20 MHz (equivalent to 0.67% in terms of normalized sensitivity) desirable for segregating nearly resembling dielectric constants. Several standard dielectric samples are tested for the performance validation revealing that the proposed sensor is efficiently differentiating between Plexiglass ( ε
_r
= 2.6) and PVC ( ε
_r
= 2.65). Simultaneously, the sensor is accurately determining even the low loss tangent of Teflon (tan δ = 3.2×10
^-4
). The measurement results are in close agreement with the references available in the literature. A thorough comparison with the state of the art literature corroborates the advantages offered by the proposed sensor and hence, its usability. Apart from characterizing the commercial grade dielectrics, this resonator is also potentially appropriate for designing high performance RF filters, oscillators and other devices.