# Smart Gateway for Healthcare Networks Based on Beam Steering Technology
## 3 Directivity Measurements
### Beam Steering Function
Figure 16 shows a photograph of the fabricated antenna with the beamforming network described in Figure 15. Four dipole antennas (#1-#4), which are mounted on a circle with a radius \(a\), are employed in the form of a spertopf dipole antenna, which is easy to adjust in terms of the element length of the antenna. However, we cannot locate it at the center of the circle because it has a structure with a spertopf balun. Therefore, another dipole antenna (#5) is used as a sleeve dipole antenna. The length of the dipole antenna is 6.8 cm (0.45 \(\lambda\)). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & & \(\mathbf{\phi}\) = 0\({}^{\circ}\) & & & \(\mathbf{\phi}\) = 22.5\({}^{\circ}\) & & & \(\mathbf{\phi}\) = 45\({}^{\circ}\) & \\ \cline{2-10}  & \(\mathbf{w}\) & \(\mathbf{w^{2}}\) & **Att. [dB]** & \(\mathbf{w}\) & \(\mathbf{w^{2}}\) & **Att. [dB]** & \(\mathbf{w}\) & \(\mathbf{w^{2}}\) & **Att. [dB]** \\ \hline \#1 & 0.17 & 0.03 & 15.5 & 0.37 & 0.14 & 8.5 & 1.00 & 1.00 & 0.0 \\ \#2 & 0.42 & 0.18 & 7.5 & 0.37 & 0.14 & 8.5 & 0.62 & 0.38 & 4.0 \\ \#3 & 0.42 & 0.18 & 7.5 & 0.50 & 0.25 & 6.0 & 0.54 & 0.29 & 5.5 \\ \#4 &Figure 17 shows the results of applying the calibration method to the measured directivity using a beamforming network composed of the weight function according to the desired angle. Figure 17a-c indicate the cases when the desired beamforming direction is set to \(0^{\circ}\), \(22.5^{\circ}\), and \(45^{\circ}\), respectively. The solid and broken curves are the measured result and the calculated outcome, respectively. The red arrows are the full width at half maximum of the measured radiation gain. It can be seen from Figure 17 that the beam direction changes depending on the desired beamforming direction, so the weight function works to control the beamforming. The measured results show a radiation pattern that is a little smaller than the calculated outcomes, but the shapes are almost identical. As can be seen from Figure 16, the cause of this radiation gain reduction is expected to a significant factor: the phase variation due to the bending of the coaxial cable between the attenuator and the antenna, which creates the error between the desired phase shift value and the phase of the cable. In addition, the full width at half maximum is somewhat wider than the analytical results illustrated in Figure 11, indicating that the approach is very suitable for beam steering. By determining the optimal weight function according to the estimated angle of the incoming wave, the beam can be continuously steered in the direction of the sensor device. Since the estimated angle of the incoming wave has an error, it is unrealistic to continuously change the weight functions. Taking advantage of the large half-width of the beamforming in the proposed antenna shown in Figure 17, we investigated the number of beam steering  
Figure 16: Fabricated antenna with a beamforming network. divisions in multiple areas at the full-azimuth angle to absorb the estimation error of the angle of the incoming wave. Figure 18 draws four division patterns of the beamforming area in the full-azimuth angle. The patterns for the four divisions are shown in Figure 18a,b. The beamforming area shown in Figure 18a indicates 90\({}^{\circ}\) intervals from 0\({}^{\circ}\). In this case, the beam is best oriented at 45\({}^{\circ}\), which is the center of the division region, so only the directivity shown in Figure 17b is used. Note that the characters (a, b, and c) in Figure 18 are associated with the directivity of Figure 17. Since the proposed antenna has a symmetrical structure, the same weight function can be applied by changing the elements connected to the beamforming network even if the beam direction changes in 90\({}^{\circ}\) intervals. In the same way, the beamforming area shown in Figure 18b has 90\({}^{\circ}\) intervals from 45\({}^{\circ}\), and only the directivity shown in Figure 17a is used. Two patterns with finer divisions in all directions were considered.