Steady-state field and group index measurements. (a–c) Experimentally measured and (c–e) numerically calculated steady state electric field distributions at the top xz- surface of the structure for frequencies (a–d) 7.52 GHz, (b–e) 7.80 GHz and (c–f) 7.91 GHz are shown. Experimentally measured average group indices for frequencies (g) 7.52 GHz, (h) 7.80 GHz and (i) 7.91 GHz are given. The colored areas denote the localization regions. The upper left insets show the calculated bandstructure for layer indexes equal to 16, 20 and 24; which are determined as the localized positions of the frequencies 7.52 GHz, 7.80 GHz and 7.91 GHz, respectively. The dashed red lines reveal the operational frequencies.