Improved Method for Permittivity Determination of Dielectric Samples by Free-Space Measurements

Abstract

A new deembedding technique is proposed for relative complex permittivity ε r determination of dielectric materials using gated free-space measurements. Its three main features are 1) it does not require any formal calibration procedure (calibration-free); 2) it is position-insensitive; and 3) it extracts ripple-free ε r due to gating process. The objective function derived to determine ε r by the proposed method is validated by free-space measurements of three dielectric samples (polypropylene, polyethylene, and polyoxymethylene). Besides, the accuracy of our method is compared with the accuracy of other calibrationfree and calibration-dependent methods in the literature.

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“…4. Different from the free-space measurement setup based on an arching reflection method in the study [36], our measurement setup, similar to those in the studies [11], [15]- [18], [37], is useful for measuring both reflection and transmission properties of prepared SCGC samples with different NS and SF additives. It includes a vector network analyzer (VNA) instrument, two horn antennas, and two coaxial-line cables [37]- [39].…”

“…Different from the free-space measurement setup based on an arching reflection method in the study [36], our measurement setup, similar to those in the studies [11], [15]- [18], [37], is useful for measuring both reflection and transmission properties of prepared SCGC samples with different NS and SF additives. It includes a vector network analyzer (VNA) instrument, two horn antennas, and two coaxial-line cables [37]- [39]. The VNA instrument (Keysight Instruments with model N9918A) Because we used the time-gating option of the VNA, to be discussed in Section IV-B, which was set around the sample region by selecting a proper time interval in the time-gating process [37] and because prepared samples had relatively larger transverse planes in square form (500 × 500 mm 2 ), it was observed that microwave absorbers positioned near the SCGC samples did not much improve our free-space measurements [38], [39].…”

“…It includes a vector network analyzer (VNA) instrument, two horn antennas, and two coaxial-line cables [37]- [39]. The VNA instrument (Keysight Instruments with model N9918A) Because we used the time-gating option of the VNA, to be discussed in Section IV-B, which was set around the sample region by selecting a proper time interval in the time-gating process [37] and because prepared samples had relatively larger transverse planes in square form (500 × 500 mm 2 ), it was observed that microwave absorbers positioned near the SCGC samples did not much improve our free-space measurements [38], [39]. For this reason, we continued our measurements without using absorbers for the sake of simplicity and easiness.…”

“…On the other hand, the larger transverse dimension (500 × 500 mm 2 ) of SCGC samples removed the diffraction effects, which might appear in their corners and edges (sharp points). Finally, the time-domain gating feature of the VNA was activated to eliminate any possible reflections from the stage that the samples were located and between transmitting and receiving horn antennas [15], [28], [37]- [39].…”

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“… 18 . These effects can also be removed by using spot-focusing antennas 15 – 17 which in turn limit the frequency band and increase overall budget of the measurement system especially for high-frequency measurements. Another issue related to free-space measurements is the effects of undesired signals from ground or between the antenna and the sample, which can overall affect the accuracy of the measurements.…”