# Potential of Sub-GHz Wireless for Future IoT Wearables and Design of Compact 915 MHz Antenna
## 5 Prototype Fabrication and Measurements
### Radiation Pattern  
A detailed explanation of the measurement setup with corresponding measurement results are presented in this section. 3D Radiation Patterns of the antenna system have been measured in an AMS-8050 Antenna Measurement System [75]. The measurements have been performed considering two different scenarios: in free-space and on IXB-063 phantom column. The radiation patterns are measured at a frequency of 915 MHz. Moreover, simulations of the radiation pattern for both cases in free-space and on an IXB-063 phantom column have been reported. For the simulation of the radiation pattern of the antenna on the IXB-063 phantom column in the 3D EM model the antenna system have been placed on a lossy cylinder with \(\varepsilon_{\mathrm{r}}\) = 32.5 and \(\sigma\) = 0.5 S/m at 915 MHz, and same dimensions of the phantom according to the measurement setup. In Figure 12a the 3D radiation pattern measurement setup in free-space scenario is depicted. The antenna system is positioned in order to rotate accordingly to the rotation of the multi-axis positioner (MAPS). The latter is characterized by a turret that enables rotation on the \(\varphi\) axis; the turret is integrated within a rotating table which enables rotation on the \(\vartheta\) axis. The antenna system phase center is also aligned in order to make it be fixed with respect to the observation point during the measurements. In Figure 12b the measured 3D radiation pattern of the proposed antenna system in free-space is reported. The peak realized gain of the antenna results to be equal to \(-\)2.37 dBi at 915 MHz. It can be noticed also that the antenna is characterized by a dipole-like radiation pattern, with omnidirectional properties on the \(xy\) plane. In Figure 12c the simulated 3D radiation pattern of the proposed antenna system in free-space is reported. The simulated peak realized gain of the antenna results to be equal to \(-\)1.25 dBi at 915 MHz. The simulations show also that the antenna is characterized by a dipole-like radiation pattern, with omnidirectional properties on the \(xy\) plane. Slight differences can be noticed between measured and simulated radiation pattern due to the presence of the MAPS in the measurement system, which is not taken into account in 3D EM model used in simulation. Figure 11: Impedance Matching: (**a**) Smith-Chart plot of the antenna impedance without matching network (solid red line), with the matching network on-phantom (dashed green line) and with the matching network in free-space (dotted blue line); (**b**) \(\mid\)S\({}_{11}\mid\) plot of the antenna impedance without matching network (solid red line), with the matching network on-phantom (dashed green line) and with the matching network in free-space (dotted blue line). In Table 7, a comparison between measured and simulated peak realized gain and directivity of the antenna in free-space is reported. A difference between measured and simulated peak realized gain of 1.12 dB and between measured and simulated directivity of 1.37 dB is observed. The difference in these values is mainly due to the fact that the losses associated with the SMA connector, the coaxial to GCPW transition and the matching network are not considered in 3D EM model. The 3D radiation pattern measurement setup of the antenna system on the phantom column IXB-063 scenario is depicted in Figure 13a. The test measurement setup is installed in such a way to make the phase center of the antenna be fixed with respect to the observation point during the measurements. The axis of the IXB-063 phantom column is aligned with the z-axis of the coordinate system used in the 3D Radiation pattern plots in Figure 13b. The antenna system is also secured to the IXB-063 phantom column using a wrist band strap. In Figure 13b the 3D radiation pattern of the antenna system on the IXB-063 phantom column is reported. The peak realized gain of the antenna in this case results to be equal to \(-6.1\) dBi at 915 MHz.