# Compact N-Band Tree-Shaped Multiplexer-Based Antenna Structures for 5G/IoT Mobile Devices
## 5 Results and Measurements
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Measured Frequency Shift** & **Simulated Bandwidth** & **Measured Bandwidth** \\ \hline \multirow{3}{*}{Around 28 GHz} & \multirow{3}{*}{680 MHz} & 1.48 GHz & 2.55 GHz \\  & & [27.22–28.7 GHz] & [27.54–30.09 GHz] \\  & & 5.3\% & 8.8\% \\  & & 3.84 GHz & 1.98 GHz \\ Around 38 GHz & 410 MHz & [36.08–39.92 GHz] & [37.2–39.18 GHz] \\  & & 10.1\% & 5.2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dual-Band S\({}_{11}\) Parameter Characteristics. Figure 9 presents the simulated efficiency of the dual-band antenna over the frequency. Naturally two local maximums are highlighted. These maximums are according to expected since they appear adjacent to the frequencies of operation. Their magnitude is higher than 85% in both operating frequencies, an important value given the structure's compactness and size. Similarly, for the tri-band antenna, there are clearly three local maximums in Figure 10, which are once again, near the frequencies of interest, in this case 20, 28 and 38 GHz, confirming the proper functioning of the antenna. Besides the efficiency peaks, the surface current distribution also confirms the proper functioning of the feeding network, verifying once again the frequency multiplexed structure achieved. Figure 11 starts by presenting the surface current distribution at the operating frequencies of the dual-band antenna, 28 GHz and 38 GHz. It can be easily observed that, for both frequencies, only the respective resonant monopole is being fed. The opposite monopole has no current flowing at all. Figure 11: Surface Current Distribution at (a) 28 GHz and (b) 38 GHz. Figure 10: Efficiency Variation Over Frequency of the Tri-Band Antenna. Figure 9: Efficiency Variation Over Frequency of the Dual-Band Antenna. Figure 12 exhibits the respective results for the tri-band structure, denoting the surface current distribution for the three operating frequencies. Once again at each one of the resonant frequencies, only the respective monopole has any current through it, all the others remain not fed. With this, it is possible to state that the frequency multiplexing concept proposed allowed to isolate, in frequency, each radiating element, maintaining a single input feed and without requiring any additional filters. Figures 13 and 14 show the gain variation of both prototypes over frequency, highlighting the respective values at the operating frequencies. It is possible to verify that, in the tri-band case, the gain values vary between 2.5 dBi and 4.5 dBi, in the frequencies of interest and they are mainly dependent on the antenna structure. Regarding the gain of the antennas, in Figure 15 it is possible to observe the simulation and measured results of the two main radiation planes at both frequencies of interest, 28/38 GHz, for the dual band antenna. Figure 14: Gain Variation Over Frequency of the Tri-Band Antenna. Figure 12: Surface Current Distribution at (a) 20 GHz, (b) 28 GHz and (c) 38 GHz. Figure 13: Gain Variation Over Frequency of the Dual-Band Antenna. As it is natural in very compact structures, particularly in multi-band antennas, the radiation patterns obtained seem a bit distorted from what was expected to be seen in monopoles. Apart from that, the dual-band antenna presents a maximum simulated gain of 3.3 dBi at 28 GHz, while at 38 GHz that value is 3.4 dBi. When it comes to the tri-band antenna, the same two radiation planes are shown, but now for the three frequencies of interest. These results are presented in Figure 16 and a similar distortion in the radiation pattern shapes is observed. This radiating structure achieved a maximum simulated gain of 3.1, 2.5 and 4.5 dBi at 20, 28 and 38 GHz. Figure 16: Simulated and Measured Normalized Radiation Pattern of the Tri-Band Antenna at 20/28/38 GHz. Figure 15: Simulated and Measured Normalized Radiation Pattern of the Dual-Band Antenna at 28 GHz and 38 GHz.