Parameter Retrieval of Samples on a Substrate From Reflection-Only Waveguide Measurements

A microwave method has been proposed for constitutive parameters' extraction of samples on a known substrate. The advantage of this method is that it relies on noniterative reflection-only (air- and metal-backed) scattering (S-) parameters so that it is a good candidate for the characterization of samples when only one-port measurements are available. It is validated by the X-band (8.2-12.4 GHz) waveguide S-parameter measurements. A sensitivity analysis is followed to evaluate and improve the performance of our method. IEE

Differential uncertainty analysis for evaluating the accuracy of S-parameter retrieval methods for electromagnetic properties of metamaterial slabs

We apply a complete uncertainty analysis, not studied in the literature, to investigate the dependences of retrieved electromagnetic properties of two MM slabs (the first one with only split-ring resonators (SRRs) and the second with SRRs and a continuous wire) with single-band and dual-band resonating properties on the measured/simulated scattering parameters, the slab length, and the operating frequency. Such an analysis is necessary for the selection of a suitable retrieval method together with the correct examination of exotic properties of MM slabs especially in their resonance regions. For this analysis, a differential uncertainty model is developed to monitor minute changes in the dependent variables (electromagnetic properties of MM slabs) in functions of independent variables (scattering (S-) parameters, the slab length, and the operating frequency). Two complementary approaches (the analytical approach and the dispersion model approach) each with different strengths are utilized to retrieve the electromagnetic properties of various MM slabs, which are needed for the application of the uncertainty analysis. We note the following important results from our investigation. First, uncertainties in the retrieved electromagnetic properties of the analyzed MM slabs drastically increase when values of electromagnetic properties shrink to zero or near resonance regions where S-parameters exhibit rapid changes. Second, any low-loss or medium-loss inside the MM slabs due to an imperfect dielectric substrate or a finite conductivity of metals can decrease these uncertainties near resonance regions because these losses hinder abrupt changes in Sparameters. Finally, we note that precise information of especially the slab length and the operating frequency is a prerequisite for accurate analysis of exotic electromagnetic properties of MM slabs (especially multiband MM slabs) near resonance regions.Publisher's Versio

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

A new deembedding technique is proposed for relative complex permittivity epsilon(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 epsilon(r) due to gating process. The objective function derived to determine epsilon(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

Determination of error-corrected full scattering parameters of a two-port device from uncalibrated measurements

A methodology relying on relating terms of a two-port error network to the scattering (S-) parameters of a two-port network or device is applied to extract its full S-parameters. The new methodology has only one sign ambiguity problem (two solutions) in evaluation of S-11 (and thus S-22) while the similar methodology in the literature has two sign ambiguity problems (4 solutions). This ambiguity problem of our method is shown to be eliminated by applying an approach based on continuity of the argument of S-11 in the frequency domain. On the other hand, our methodology, as compared with the thru-reflect-line calibration technique, does not necessitate usage of any reflection standard in determining full S-parameters of a two-port network or device. Finally, it gives information about error networks. For its validation, S-parameters of a microwave phase shifter and a polyethylene sample flushed with the left/bottom terminal of the coaxial cell were extracted

New formalism for characterization of simple non-reciprocal networks free from singularity-point problem

A method has been proposed for accurate characterization of non-reciprocal networks without enforcing the passivity principle. Thanks to the introduced different even and odd coefficients, our method has no singularity-point problem as compared with the conventional method. The proposed method is validated by scattering parameter measurements of a ferrite-loaded waveguide shifter. In addition, it is demonstrated by measurements that our method, as compared with the conventional one, is more resistant to random noise due to post-calibration effects

Mechanical and Electromagnetic Properties of Self-Compacted Geopolymer Concretes With Nano Silica and Steel Fiber Additives

Mechanical and electromagnetic properties (over 2-16 GHz) of self-compacted geopolymer concrete (SCGC) samples with different amounts of nanosilica (NS) and steel-fiber (SF) have been examined. From the mechanical tests, it is observed that, while the amount of NS added to SCGC samples does not make any noticeable change in compressive strength and modulus of elasticity values, an increase in the amount and/or aspect ratio of SF additives improves these values. From the electromagnetic tests, it is noted that the effect of SF on the reflection properties of SCGC samples is relatively smaller than the effect of NS. Besides, while the incorporation of NS improves the resonance characteristics of transmission properties, additives of SF decrease these properties over the entire frequency band. Finally, sample C7, which has 1% SF with a smaller diameter and 2% NS in reference to the mass of the binder, has the optimum NS and SF additives, producing maximum absorbance values