To verify the propagation characteristics experimentally in the microwave regime, the proposed structure was constructed from absorption free Al2O3 rods (see Fig. 6). Prior to performing the experimental analyses, the coupling efficiency has been numerically estimated to be in the range of 65–71% and experimentally in the range of 62–74%. The numerical estimation was based on the termination of the simulations at the specific time step where the initial reflections due to air-PhC coupling mismatch have been completely gone through the reflection monitor. Experimentally, on the other hand, a strong microwave absorber was placed inside the PhC structure to similarly avoid the chirping reflections and to account only for the reflections arising from the coupling mismatch. The discrepancy between the experimental and numerical estimations stems mainly from the additional reflections and interferences inside the receiver antenna’s metallic aperture and to the non-ideal absorption (approximately 95%) of the microwave absorber. In contrast to the calculations, in our experimental setup (see Fig. 6) we could scan the electric field distribution only at the top surface of the structure. The monopole antenna was kept parallel to the y- axis and the tip of the antenna was placed 2 mm above the top of structure. A motorized linear stage was used to move the monopole antenna with 1 mm lateral resolutions in the x- and z- directions, as shown in Fig. 6. In this way, the y- component of the electric field at the top surface of the structure was measured and shown in Fig. 7(a–c) for frequencies equal to 7.52 GHz (a/λ = 0.450), 7.80 GHz (a/λ = 0.467) and 7.91 GHz (a/λ = 0.473), respectively. On the other hand, the electric field distribution was numerically calculated at the same surface and is in Fig. 7(d–f) for frequencies equal to 7.52 GHz, 7.80 GHz and 7.91 GHz, respectively. Comparing Fig. 7(a) with Fig. 7(d), Fig. 7(b) with Fig. 7(e) and Fig. 7(c) with Fig. 7(f), we note that the turning points in the numerical and experimental cases are in good agreement. We attribute the discrepancy in the field distributions between the two cases to the difference of the experimental and numerical source beam shapes.Figure 6Microwave experimental setup. Schematic illustration of the experimental setup is shown. The lower left inset depicts the photographic view of the constructed woodpile PC. Figure 7Steady-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.