# Dual-Polarization Conversion and Coding Metasurface for Wideband Radar Cross-Section Reduction
## 6 Experimental Results  
To experimentally validate the properties of the designed 1-bit CM, 5 \(\times\) 5 lattices with a total size of 180 \(\times\) 180 mm\({}^{2}\) were fabricated, as illustrated in Figure 12a. Printed circuit technology was employed to etch metallic copper patterns onto the thin layer of the Rogers RT5880 substrate. The Rogers RT5880 layer had a thickness of 0.127 mm, while the metal layer was 35 \(\upmu\)m thick. On the back side of the substrate, which includes an air gap, a metallic copper plate was employed to achieve complete reflection. The measurements were conducted in an anechoic chamber to eliminate environmental noise and reflections, ensuring precise results, as depicted in Figure 12b.  
The reflected waves were measured using two different sets of linearly polarized horn antennas, covering two frequency sweeps (8-18 GHz and 18-40 GHz). These antennas were connected to an Agilent vector network analyzer N5230. The antennas' centers should align with the center of the sample for accurate measurements. In order to calculate LP-CP conversion, it is necessary to measure both the co-polarized and cross-polarized reflection coefficients. Hence, two horn antennas were aligned in the same orientation,  
Figure 11: RCS reduction of 1-bit coding metasurface at different incident angles (\(\theta^{\circ}\)).  
Figure 12: (**a**) Prototype of 1-bit CM, and (**b**) experimental setup.  
either vertically (\(y\)-polarized) or horizontally (\(x\)-polarized), to measure the co-reflection coefficient. For measuring the cross-reflection coefficient, the transmitting antenna was placed vertically, while the receiving antenna was positioned horizontally. Figure 13a illustrates the conversion performance of a planar CM from linear polarization to circular polarization under normal incident waves. From Figure 13a, it is evident that an axial ratio of less than 3 dB is achieved within different frequency ranges of 11.80-12.29, 13.17-18.44, and 33.33-40.35 GHz. Additionally, the axial ratio values remain consistently below 3 dB in the frequency bands, as mentioned above. Nevertheless, in monostatic RCS measurement, it is necessary to maintain a separation of over 2 m between the antennas and the sample to fulfill the far-field condition. The angular separation between antennas must be kept under 5\({}^{\circ}\). The gate-reflect-line calibration was employed to effectively filter out additional noise and interference from the surrounding environment. A metal sheet of the same size was also measured as a reference to determine the actual reduction in the radar cross-section. Figure 13b illustrates the simulated and measured results of the radar cross-section reduction for the planar surface. A reduction in the RCS of more than 10 dB is observed within a single frequency band, specifically from 13.1 to 13.80 and 20.4 to 30.9 GHz. The simulated and measured results show good agreement, but there was minimal impact on the radar cross-section reduction due to channeling and experimental effects. Nonetheless, minor discrepancies between the simulation and measurement results occur due to manufacturing and measurement errors, such as misaligned horn antennas and the finite number of unit cells in the MS structure.  
Table 1 compares the performance of the proposed metasurface with that of a recently published article. Our compact design achieves maximum linear polarization and linear-to-circular polarization conversion, as demonstrated by the data presented in Table 1. This dual-polarization capability with angular stability is a key feature of our design. In [35], the cited work exhibits good angular stability, although the polarization conversion ratio (PCR) falls below the proposed design. Additionally, these works operate within dual-frequency bands. The results indicate that the proposed structure performs well in both RCS reduction and LP-CP conversion.  
Figure 13: Measured and simulated results of (**a**) (AR \(\leq\) 3 dB) and (**b**) monostatic RCS reduction.