# A Compact Sub-GHz Wide Tunable Antenna Design for IoT Applications
## 3 Results of Simulation and Measurements
### Radiation Patterns  
The radiation characteristics of the proposed antenna design at different frequency bands characterize the antenna. The proposed antenna simulated 3-D gain patterns at 885 MHz and 1029 MHz are shown in Figure 7a,b, respectively. The gain patterns of the proposed antenna design, omnidirectional behavior was observed at the resonating bands. The gain patterns that result from simulation and measurements and antenna efficiency (\(\%\eta\)) values of the antenna are listed in Table 1 and are shown in Figure 8. From the resulting values, it can be concluded that the proposed antenna will have good performance when operating in the sub-GHz bands. Figure 6: Surface current density at (**a**) 1950 MHz, (**b**) 1750 MHz, (**c**) 964 MHz, and (**d**) 764 MHz. The proposed antenna design radiation characteristics were validated by performing measurements with the setup shown in Figure 9. The 2D simulated and measured gain patterns at 885 MHz and 1029 MHz are shown in Figure 10 for \(\varphi\) = 0\({}^{\circ}\) and \(\varphi\) = 90\({}^{\circ}\) cut. It can be observed that in the given mode of operation at each resonating band, the antenna has omnidirectional behavior. Figure 10a,b show the simulated and measured radiation patterns for \(\varphi\) = 0\({}^{\circ}\) cut while Figs. Figure 10c,d show the simulated and measured radiation patterns for \(\theta\) = 90\({}^{\circ}\). The proposed work is intended to be utilized in 5G-enabled IoT devices that mostly operate at lower power. Therefore, with typical signal power densities, this antenna would work well. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{4}{c}{**Simulated Results**} & \multicolumn{3}{c}{**Measured Results**} \\ \hline \(\mathbf{f_{s}}\) (MH) & **PG (dBi)** & **\%\(\eta\)** & **\(\mathbf{f_{m}}\) (MHz)** & **PG (dBi)** & **\%\(\eta\)** \\ \hline
764 & 0.86 & 55 & 758 & - & - \\ \hline
836 & 0.98 & 60 & 827 & 0.86 & 54 \\ \hline
885 & 1.2 & 63 & 875 & 0.96 & 59 \\ \hline
964 & 1.4 & 67 & 976 & 1.13 & 64 \\ \hline
1029 & 1.8 & 70 & 1033 & 1.42 & 67 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Peak gain (PG) and efficiency (%\(\eta\)) values of the proposed antenna. Figure 8: Simulated and measured realized gains (a) 2.09 pF, 2.5V (b) 0.84 pF, 15V. Figure 7: Simulated 3-D antenna gain patterns at (a) 885 MHz (b) 1029 MHz. Table 2 presents a detailed comparison that compares the distinguishing features of the most relevant IoT antennas available in the literature. The various features included antenna type, size, bands covered, suitability for NB-IoT operation, %\(\eta\), planar structure, percentage miniaturization obtained, continuous frequency sweep, and the number of sub-GHz NB-IoT bands covered. Most of the IoT antennas reported are either wide-band monopole (MP) or non-planar PIFA designs. For such antennas, it is quite challenging to obtain a sub-GHz continuous frequency sweep over a wide band. Although, the proposed antenna design is competitive in terms of its compactness with some of the available designs, it outperformed in sub-GHz bands with wide tunability and NB-IoT operation  
Figure 9: Antenna’s farfield measurement setup. for better power management, long battery life, and enabled devices for long-distance communications, etc. In Table 2, the proposed is compact and better than [2; 3; 4; 5; 6; 15; 2; 7; 8; 9; 16; 17; 18; 19; 20; 21; 22; 23], and [32; 33; 34; 35; 36] in terms of antenna size. Although, some work as cited in [4; 6; 15; 16; 17; 18; 19; 21; 23] covered single sub-GHz bands but without tuning capability to switch between different bands. Some of the designs as presented in [4; 6; 15; 16; 17; 18; 19; 21; 23] are good for covering the sub-GHz band, but the majority of them are not suitable for NB-IoT operations.