# Broadband Flexible Microstrip Antenna Array with Conformal Load-Bearing Structure
## 4 Analysis of Simulation and Measurement Results
### Antenna Array  
The measurement environment and prototype of the fabricated antenna array are depicted in Figure 15. Its simulated and measured reflection coefficient has been plotted in Figure 16. On account of the mutual coupling between the antenna elements, the bandwidth of the antenna array has been broadened. In the flat state, its measured operating frequency band is 11.67-13.76 GHz and 14.33-14.825 GHz with a relative bandwidth up to 20.68%. In a bending state, the deformation of the power divider leads to impedance discontinuity in the microstrip line, and this is typically a complex problem that affects the transmission of electrical signals. Since electrical signals can be maintained by the coupled aperture, in the deformation with 30\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\) in the _yoz_ plane, the operating frequency band of the antenna array still covers 11.08-14.1 GHz, 10.63-13.5 GHz, and 11.55-14.33 GHz, and their relative bandwidths are 24.16%, 23.82%, and 23.12%, respectively. In Figure 17, its simulated and measured gain and cross-polarization radiation patterns are shown at 12.5 GHz. With the increment of bending angle, the cross-polarization of the antenna array is boosted, and the distortion of the antenna array radiation pattern occurs. The peak gain of the antenna array keeps stable radiation at the _z_-axis, both in a flat state and under different bending states. The performance characteristics of the proposed antenna array are listed in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**State** & **BW** & **Peak Gain (dBi)** & **3 dB Beam Angle (\({}^{\circ}\))** \\ \hline Planar & 20.68\% & 8.32 & 67.0 \\
30\({}^{\circ}\) & 24.16\% & 8.25 & 67.4 \\
60\({}^{\circ}\) & 23.82\% & 8.12 & 67.8 \\
90\({}^{\circ}\) & 23.12\% & 8.03 & 68.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Performance characteristics of the proposed antenna element.  
Figure 14: Simulated and measured results for gain radiation patterns and cross-polarization radiation patterns of the proposed antenna element in flat state and under various bending states at 12.5 GHz, (**a**–**h**) E-plane and H-plane with various states.  
Figure 16: The simulated and measured reflection coefficient of the proposed antenna array under various bending states and on the plane. The inset illustrated the bending state.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**State** & **BW** & **Peak Gain (dBi)** & **3 dB Beam Angle (\({}^{\circ}\))** \\ \hline Planar & 20.68\% & 14.7 & 38.6 \\
30\({}^{\circ}\) & 24.16\% & 14.4 & 37.8 \\
60\({}^{\circ}\) & 23.82\% & 12.9 & 38.7 \\
90\({}^{\circ}\) & 23.12\% & 12.7 & 39.1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance characteristics of the proposed antenna array.  
Figure 15: The photograph of the proposed antenna array: (**a**) measurement environment, (**b**) top layer with radiation patches, (**c**) the ground with coupling apertures on the middle layer, (**d**) the feeding network with Wilkinson power divider and ground with four coupling apertures on the middle layer, and (**e**) reflection surface on the back surface of the lower substrate layer.