# Extremely Low-Profile Monopolar Microstrip Antenna with Wide Bandwidth
## 3 Implementation and Measurement Results
It is analyzed that the reason that the measured results was higher than those of the simulation at approximately 5.6 GHz was reflected by the additionally radiated electromagnetic radiation from the 12 mm-long coaxial cable and the measuring cable connected to the proposed antenna. The deviation between the simulation and the measurement result is considered to be a reasonable value within the calibration error range occurring in the anechoic chamber. Figure 8 exhibits the far-field radiation patterns of the proposed antenna. The radiation patterns were measured at the test frequencies of 5.54 GHz supported by the maximum antenna realized gains, which showed that the patterns were omni-directional, that is, monopolar radiations with co-polarization of the vertical linear polarization. As expected, the proposed antenna was identical to the monopole antenna mounted vertically with the radiation pattern and the polarization, as shown in Figure 8a. The measured peak gains were observed at \(\theta=40\) degree, as shown in Figure 8b. At the test frequency of 5.54 GHz, the directivity of the proposed antenna was different from that of an ideal monopole, that  
Figure 7: Simulated and measured results of the proposed antenna: (**a**) reflection coefficients and (**b**) realized antenna gains. is, an electrically small antenna due to the radiator of 1.5 wavelength. At \(\theta=40\) degree, as shown in Figure 8b, the horizontal polarization (\(E\varphi\)), that is, the cross-polarization of the proposed antenna, was observed to be \(-30.45\) dB at the normalized radiation pattern. The proposed antenna successfully demonstrated omni-directional radiation in the simulation results, and the hypothesis of the degenerated TM\({}_{02}\) mode of the proposed antenna holds. The key performances of the proposed antenna and the recent monopolar microstrip antennas are summarized in Table 2. This study reports a minimum thickness of the substrate over 10 times higher than the previous results in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline
**Ref., Work Year** & **Ground Size, mm\({}^{2}\) (\(I\)/\(\lambda_{\text{min}}\)1)** & **Height, mm (\(I\)/\(\lambda_{\text{min}}\)1)** & **BW(\%)** & **Antenna Type** \\ \hline
[30], 2009 & \(35\times 35\) & 0.76 & & \\  & (0.502 \(\times\) 0.502) & (0.011) & & \\  & \(\pi\times 32\times 32\) & 3 & & \\
[7], 2016 & \(\pi\times\) (0.514 \(\times\) 0.514) & (0.048) & 32.2\% & Monopolar Microstrip \\  & \(\pi\times\) 30.8 \(\times\) 30.8 & 6.3 & & \\
[33], 2016 & \(\pi\times\) (0.572 \(\times\) 0.572) & (0.117) & 15.4\% & Monopolar Microstrip \\  & \(\pi\times\) 80 \(\times\) 80 & 10 & & \\
[10], 2019 & \(\pi\times\) (0.987 \(\times\) 0.987) & (0.123) & 12.7\% & Monopolar Microstrip \\  & \(\pi\times\) 130 \(\times\) 130 & 3.18 & & \\
[34], 2017 & \(\pi\times\) (2.5 \(\times\) 2.5) & (0.08) & 2.3\% & Tripolarized Monopolar Microstrip \\  & \(\pi\times\) 113 \(\times\) 113 & 10.508 & & \\
[35], 2019 & \(\pi\times\) (0.859 \(\times\) 0.859) & (0.08) & 14.0\% & Tripolarized Monopolar Microstrip \\  & \(\pi\times\) 120 \(\times\) 120 & 9.2 & & \\
[36], 2019 & \(\pi\times\) (0.876 \(\times\) 0.876) & (0.07) & 24.45\% & Tripolarized Monopolar Microstrip \\  & \(\pi\times\) 35 \(\times\) 35 & 1.6 & & \\  & \(\pi\times\) (0.651 \(\times\) 0.651) & (0.03) & & \\ This Work & \(\pi\times\) 35(0.651) \(\times\) 35(0.651) & 0.254 & & Monopolar Microstrip \\  & & (0.0044) & 15.24\% & Monopolar Microstrip \\ \hline \end{tabular}
\end{table} 
Table 2: Performance comparison of state-of-the-art monopolar microstrip antenna. Figure 8: Far-field radiation patterns of the proposed antenna at the resonant frequency of 5.54 GHz: (**a**) \(H\)-plane (_xy_-plane) and (**b**) \(E\)-plane (_zx_-plane).