# Development of a Metalens for Radio Wave Ground- Penetrating Radars
## 3 Experimental Study  
To conduct an experimental study, a previously simulated material was made on the basis of ring elements located according to the data obtained in the simulation. The developed layout of the structure is shown in Figure 9 At the current stage, an experimental layout for one antenna was created; this approach allowed us to test the possibility of focusing. To verify the simulation, a setup was developed that allows one to see the distribution of the field at a distance from the surface of the metamaterial after radiation by the antenna from the georadar. The installation diagram is shown in Figure 9a. The setup consisted of an antenna (1) (Figure 9b), an experimental metamaterial sample (2) (Figure 9c), and a two-coordinate scanner (3) with a receiving antenna (4), both antennas connected to the PNA-L NetworkAnalyzer of the Agilent Technologies company. The scanner was rearranged at different distances from the metamaterial, starting from 10 cm and, then, with a step of 20 cm, up to 110 cm. The data were obtained in the frequency range of 0.5-3 GHz. The construction of the obtained wave projections was carried out using digital processing of the recorded  
Figure 8: The dependence of the width of the focus area on the frequency. Figure 9: Experimental setup for testing the focusing properties of a metamaterial. Installation scheme (**a**), Top view of the installation without metamaterial (**b**), Top view of the installation with metamaterial (**c**), Side view of the installation with metamaterial (**d**). amplitude-phase distribution of the field. These algorithms were used in the work. The principle of UWB data processing is based on the technology of aperture synthesis and software and hardware focusing of radiation. The method of synthesizing the aperture consists of the fact that the radar data received at each moment of sounding time are stored together with the data on the location of the receiving antenna corresponding to these time periods. The image was constructed by successively summing the received signals with the equalization of the time delays of the pulses scattered by a point with given coordinates. To do this, delays were introduced into the received signal, corresponding to the total time of signal propagation from the transmitter to the object and back. To do this, the delay time was calculated for each of the pulses. In this case, all signals registered at different points of emission-reception were summed in phase for each given point with the correction of the existing delay. Figure 10 shows the distribution of the field amplitude over the scanning surface at different heights from the metamaterial at a frequency of 2 GHz. It can be seen that, as the distance from the metamaterial increases, the electromagnetic field begins to gather into a beam and, at a distance of 50 cm, is focused into a spot with transverse dimensions of 12 cm and continues to decrease. Starting from a distance of 70 cm, the size of the main lobe decreases to a size of 7 cm and remains the same as the distance increases. It can also be observed that, at a small distance, the spot is rather blurred. This experiment shows the consistency of the simulation and allowed us to find the application of such a configuration in a georadar. For a comparison, an experimental study of the focusing properties of the antenna without the developed metamaterial was also carried out. The resulting distributions of the electric component of the field are shown in Figure 11.  
The focusing properties were considered at a distance of 70 cm (**a**) and 90 cm (**b**). Such heights were chosen on the basis of an earlier experiment with a metamaterial. As can be seen from the obtained images, although the electric component of the field is narrowed by 90 cm (Figure 11b), the resulting focusing spot is quite blurry and has dimensions of at least 17 cm. Thus, the use of the developed material makes it possible to focus the radiation from the antenna.