# Wideband Ring-Monopole Flexible Antenna with Stub for WLAN/C-Band/X-Band Applications
## 3 Antenna Fabrication and Analysis  
### Antenna Fabrication and Antenna Characteristics  
The antenna was fabricated by printing a copper radiating surface on a 0.2 mm polyimide substrate with a dielectric constant of 3.5. Figure 7 is a picture of the fabricated antenna and a picture of when the SMA connector was attached for measurement. S-parameters were measured using the vector network analysis (VNA) model ZVA67. In addition, gain measurement was performed at the Korea Electromagnetic Waves Technology Institute. Figure 8 compares the results of measuring the S-parameter of the manufactured antenna and the S-parameter of the simulation. Furthermore, Figure 9 compares the matching characteristics of the fabricated antenna with the simulation using VSWR. The measured data and simulations show reasonably consistent graphs. There is a slight difference between the simulation result and the measurement result. This could be seen as the effect of soldering the SMA connector to the measurement antenna and the loss effect of the connected cable. The simulation results and measurement results differ more at high frequencies than at low frequencies. This is because the antenna is more sensitive to soldering or connected cables at high frequencies. In the simulation, the S-parameter was formed below \(-10\) dB in the band of 2.31-2.78 GHz, 3.39\(\sim\)11.73 GHz. However, in the measured value, it had a bandwidth of 2.36 GHz-2.87 GHz, 3.4 GHz-12 GHz. The measured results showed that the antenna could operate in WLAN (2.4-2.48 GHz, 5.1-5.8 GHz)/C-band (4-8 GHz)/X-band (8-12 GHz). Figure 6: S-parameter according to the size of Wsh1. Figure 7: Photo of the antenna; (a) antenna without SMA connector; (b) antenna with SMA connector. The radiation efficiency and polarization of the proposed antenna are shown by simulation. Figure 10 is the simulated radiation efficiency of the proposed antenna, and Figure 11 is the axial ratio of the proposed antenna. Radiation efficiency was close to 100% at the antenna operating bandwidth. The axial ratio showed that the proposed antenna had a linear polarization. Figure 8: Comparison of the antenna S-parameters between measurement and simulation. Figure 10: Simulated radiation efficiency of the proposed antenna. Figure 9: Comparison of the antenna VSWR between measurement and simulation. Figure 12 compares the 2D radiation patterns between measurements and simulations at 2.4, 3.5, 6.3, and 10 GHz, which appeared as resonance frequency in S-parameters. At 2.4 and 3.5 GHz, a radiation pattern close to omnidirectional is shown, but the distortion of the radiation pattern as it goes to a high frequency is due to the high order mode. The proposed antenna had a gain of 1.3 dB at 2.4 GHz, 1.6 dB at 3.5 GHz, 1.3 dB at 6.3 GHz, and 1.7 dB at 10 GHz. Figure 13 is a simulated 3D radiation pattern. The 3D radiation pattern showed that the antenna was distorted by the higher-order mode at high frequencies. Figure 11: Simulated axial ratio of the proposed antenna. Figure 12: _Cont._  
Figure 12: Comparison of the antenna 2D radiation pattern between measurement and simulation. (**a**) E-plane at 2.4 GHz; (**b**) H-plane at 2.4 GHz; (**c**) E-plane at 3.5 GHz; (**d**) H-plane at 3.5 GHz; (**e**) E-plane at 6.3 GHz; (**f**) H-plane at 6.3 GHz; (**g**) E-plane at 10 GHz; (**h**) H-plane at 10 GHz. Figure 13: _Cont._  
Figure 14 shows the peak gain of the antenna for each frequency. The gain was the lowest at 2.87\(\sim\)3.4 GHz, where the antenna was not operating. Furthermore, compared with Figure 8, in the band where the antenna operates, it can be confirmed that the S-parameter  
Figure 13: Simulated antenna 3D radiation pattern of the proposed antenna; (**a**) 3D radiation pattern at 2.4 GHz; (**b**) 3D radiation pattern at 3.5 GHz; (**c**) 3D radiation pattern at 6.3 GHz; (**d**) 3D radiation pattern at 10 GHz. had a large influence on the gain tendency.