# Compact N-Band Tree-Shaped Multiplexer-Based Antenna Structures for 5G/IoT Mobile Devices
## 5 Results and Measurements  
The previously described prototypes were simulated and built and they are shown in Figure 6. It is important to mention that regarding the tri-band structure, Figure 6b presents a connectorized version of the antenna, where the length of the 50 \(\Omega\) input feed line is excessive and just needed to place the connector. The antennas were measured, and the main results obtained are presented throughout this section. Figure 7 exhibits the simulated and measured results of the reflection coefficient for the dual-band structure. For this prototype, a good impedance matching was achieved, with both curves presenting a similar behavior despite some frequency shifts of 680 MHz and 410 MHz from the desired 28 and 38 GHz, respectively. These small discrepancies seen might be justified either by slight construction imperfections (which is something natural given the antennas' small size). Nevertheless, the measured values of S\({}_{11}\) at the operation frequencies are \(-\)13.64 dB and \(-\)16.94 dB, respectively, making of these results quite satisfactory. Regarding the bandwidth, and considering the S\({}_{11}\) < 10 dB criteria, the prototype achieved an operating band of 2.55 GHz [27.54-30.09 GHz], representing 8.8% bandwidth around 28 GHz. On the other hand, around 38 GHz, a 1.98 GHz [37.2-39.18 GHz] band was reached, meaning 5.2%. Table 3 summarizes the measured and simulated results of the dual-band radiating element. Figure 6: Prototypes Built: (**a**) Dual-Band and (**b**) Tri-Band Antennas. Figure 7: Simulated and Measured Reflection Coefficient of the Dual-Band Antenna. The second prototype built proves the concept here proposed in a tri-band antenna. Figure 8 identifies a reasonable impedance matching between simulated and measured results in respect to the reflection coefficient, since the minimum value for S\({}_{11}\) occurs at the frequencies of interest, despite the slight frequency shifts around 20 GHz and 38 GHz. These minor mismatches can be once again justified by the same reasons presented for the previous prototype: construction imperfections, or dielectric permittivity variations. Regarding the first operation band (at 20 GHz), the antenna shows a measured bandwidth of 0.62 GHz, equivalent to 3%. At the other operation frequencies, 0.4 GHz and 2.16 GHz are seen at 28 and 38 GHz respectively. Table 4 summarizes the measured and simulated results of the tri-band radiating structure. Through the reflection coefficient of the latest prototype analyzed it is possible to confirm the adequacy of the prototypes built and more importantly the principle of design proposed seems to guarantee the impedance matching. Other aspect that sustains the appropriate performance of these antennas in 5G and the massive IoT scenario is the information about the antennas' efficiency, which is presented in Figures 9 and 10, regarding the dual and the tri-band radiating structures, respectively. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Measured Frequency Shift** & **Simulated Bandwidth** & **Measured Bandwidth** \\ \hline \multirow{3}{*}{Around 20 GHz} & \multirow{3}{*}{330 MHz} & 0.88 GHz & 0.62 GHz \\  & & [19.56–20.44 GHz] & [20.05–20.67 GHz] \\  & & 4.4\% & 3\% \\  & & 0.29 GHz & 0.4 GHz \\ Around 28 GHz & 190 MHz & [27.64–27.93 GHz] & [27.61–28.01 GHz] \\  & & 1.1\% & 1.4\% \\  & & 4.03 GHz & 2.16 GHz \\ Around 38 GHz & 1.5 GHz & [34.60–38.62 GHz] & [35.45–37.61 GHz] \\  & & 11\% & 5.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tri-Band S\({}_{11}\) Parameter Characteristics. Figure 8: Simulated and Measured Reflection Coefficient of the Tri-Band Antenna.