## 7 Active Transparent Antenna Results and Discussion  
The fabrication method for the transparent antenna was showcased in Section 4. The technique and procedure for achieving transparency in the antenna remain consistent, with the only distinction being the utilization of individual masks for each antenna. It is important to note that, in the case of the active antenna, diodes are employed in place of the metallic strip. The fabricated active antenna is presented in Figure 10.  
Figure 11a presents a detailed view of the central section of the transparent antenna before the PIN diodes are installed. In contrast, Figure 11b illustrates the identical region after the diodes have been incorporated.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**States** & **V1** & **V2** & & \\ \hline State 1 & \(>\)0 & \(<\)0 & V1 \(>\) V2 & V1 = 2.9 V, V2 = \(-\)2.9 V \\ \hline State 2 & \(<\)0 & \(<\)0 & V1 \(<\) V2 & V1 = \(-\)4.3 V, V2 = \(-\)2.9 V \\ \hline State 3 & \(>\)0 & \(>\)0 & V1 \(<\) V2 & V1 = 2.9 V, V2 = 4.3V \\ \hline \end{tabular}
\end{table}
Table 1: Configuration states.  
\begin{table}
\begin{tabular}{c c c c} \hline
**State** & **D1** & **D2** & **D3** \\ \hline State 1 & ON & ON & OFF \\ \hline State 2 & OFF & ON & ON \\ \hline State 3 & ON & OFF & ON \\ \hline \end{tabular}
\end{table}
Table 2: Diodes’ states.  
Figure 9: Feeding strategy and geometries of the active antenna: (**a**) front side, (**b**) back side, and (**c**) diodes’ states.  
Figure 12 provides a close-up view of the biasing section used for the active transparent antenna. It utilizes a DC-feed inductor and resistor protection mechanism.  
To assess the performance of the active transparent antenna, we present the return losses depicted in Figure 13. It is worth mentioning that the experimental measurements exhibit fluctuations or ripples, which could be attributed to potential errors in the measurement process.  
The active transparent prototypes demonstrate improved matching compared to the results shown in Figure 3 for the opaque passive antenna and Figure 8 for the transparent passive antenna. This enhancement could be attributed to the inclusion of PIN diodes and their associated losses. The antennas show a capacity to operate within a frequency range from approximately 15 to 48 GHz for state 1, with a range from 17 to 48 GHz for states 2 and 3.  
Figure 11: Zoomed view using an optical microscope. Mesh ground with the petals (**a**) before the implementation of the diodes, (**b**) after the implementation of the diodes.  
Figure 12: The positions of the inductor and resistor in the fabricated active antenna.  
Figure 10: The active transparent antenna that has been fabricated.  
As depicted in Figure 14, the radiation pattern orientation can be altered as anticipated by adjusting the DC bias of the diodes.  
Figure 15 showcases the gain results for each state of the antenna, presenting a comprehensive overview that includes both the measured and simulated outcomes.  
In the simulation, state 1 exhibits a gain of 6.5 dBi at 26 GHz, while the measured gain at the same frequency is 6.7 dBi. For state 2, the simulation shows a gain of 4.4 dBi, whereas the measured gain is 4 dBi. In the case of state 3, the simulation yields a gain of 5.5 dBi, while the measured gain is 5.1 dBi, with both detected at the same frequency. The variation in gain can be attributed to the increased level of rear radiation in states 2 and 3. Importantly, the comparison between the simulated and measured results demonstrates good agreement.  
Figure 14: Measured radiation patterns \(\mathrm{E}_{\varphi}\) versus \(\varphi\) of active transparent antenna operating in (a) state 1, (b) state 2, and (c) state 3 at frequencies of 26, 27, and 28 GHz.  
Figure 13: Return losses of the transparent active antenna.  
Figure 15: A comparison of the gain between simulations and measurements for the active transparent antenna operating in states 1, 2, and 3.