Two optimiser approach to transmission line metamaterial dispersion characterisation

The left-handed propagation behaviour of metamaterial structures offers a new paradigm for electromagnetic device and antenna design. To exploit the potential of such structures, accurate methods for characterising the dispersion of a given structure are required. A Bloch-Floquet analysis can be used to retrieve the complex propagation coefficient and Bloch impedance of the corresponding infinite cascade of unit cells, using knowledge of the unit cell´s electrical characteristics (such as equivalent circuit, 2-Port or effective media parameters or eigenfrequencies). However inaccuracies in the extracted dispersion information can arise if assumptions regarding the form of the equivalent circuit or structure homogenisation are not met, or if errors in extracted parameters propagate through the solution. As an example Figure 1 illustrates the effect of overlooking component losses and parasitic elements, creating a large disparity between the predicted frequency response calculated assuming ideal lossless L and C component values and the measured performance. Correct diagnosis of the cause of such behaviour can reduce design time, improve device yields and achieve accurate dispersion extraction.