# Design of 1-Bit Digital Reconfigurable Reflective Metasurface for Beam-Scanning
## 3 Results and Discussion
### Simulation and Experimental Results of the RRM  
Figure 6 shows the radiation pattern of the 1-bit digital RRM when the main beam direction is \(0^{\circ}\), \(30^{\circ}\) and \(60^{\circ}\), respectively. From the simulation results, the characteristics of beam-scanning have been verified. For the sake of comparing the radiation characteristics in different reflection angles, the far-field performances are given in Table 2. From Table 2, we can see that when the scanning angle increases, the gain of the RRM decreases slightly. It can be seen that the 1-bit digital RRM can radiate in the same reflection angle, as assumed. The far-field radiation patterns are plotted in Figure 7 with different scanning angles and the gain of the RRM decreases slightly with the increase of the reflection angle. Then, by adjusting the coding of the 1-bit digital RRM, it can scan from \(-60^{\circ}\) to \(+60^{\circ}\). These simulation results verify the validity and practicability of the 1-bit RRM.  
Figure 5: Reflection phase characteristics versus frequencies (**a**) With different capacitance; (**b**) At 3.5 GHz.  
Figure 6: Radiation patterns of the proposed 1-bit digital RRM at (**a**) \(\theta_{r}=0^{\circ}\); (**b**) \(\theta_{r}=30^{\circ}\); (**c**) \(\theta_{r}=60^{\circ}\).  
We test the performances of the proposed 1-bit digital RRM while \((\theta_{i},\varphi_{i})=(30^{\circ},0^{\circ})\) and \((\theta_{r},\varphi_{r})=(60^{\circ},90^{\circ})\) by using fixed capacitors. The simulated and measured results are given in Figure 8. From the simulation results, the 1-bit digital RRM can work from 3.47 GHz to 4.23 GHz, and the relative bandwidth is about 22%. The actual 3 dB bandwidth is 16.6%. The measured gain is slightly decreased. The deviation between the simulation and the measurement results may be caused by the fabrication error and capacitance error. The varactor diode is connected between the two patches by solder, which may lead to the introduction of additional impedance. The welding technique is very important because if the tin solder is too heavy much, the capacitance value of the varactor may not be the same as its original value. The additional impedance is uncontrollable and may result in errors for the measurement results. It is believed that these deficiencies will be readily compensated and thus superior radiation characteristics can be obtained. It is worth pointing out that these experimental results agree well with the simulations results. As a result, if we want to design an RRM with much wider broadband, the digital method maybe a better choice.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \((\theta_{r},\varphi_{r})\) & **Gain (dB)** & **Beam Point Error** & \((\theta_{r},\varphi_{r})\) & **Gain (dB)** & **Beam Point Error** \\ \hline \((0^{\circ},90^{\circ})\) & 19.89 & \(0^{\circ}\) & \((50^{\circ},90^{\circ})\) & 16.16 & \(0^{\circ}\) \\ \((30^{\circ},90^{\circ})\) & 18.65 & \(0^{\circ}\) & \((60^{\circ},90^{\circ})\) & 15.85 & \(0^{\circ}\) \\ \((40^{\circ},90^{\circ})\) & 17.59 & \(0^{\circ}\) & & & \\ \hline \end{tabular}
\end{table}
Table 2: The gain of the 1-bit digital RRM at different main beam directions and beam point errors for different scanning angles.  
Figure 8: Comparison of measured and simulated results of the fabricated RRM (**a**) Normalized radiation pattern at 3.5 GHz; (**b**) Gain characteristics.  
Figure 7: Scanning main beam characteristics of the 1-bit digital RRM.