# Smart Gateway for Healthcare Networks Based on Beam Steering Technology
## 2 Smart Gateway Antenna
### Beam Steering Function  
In 5G, which is currently in practical use around the world, beamforming technology is utilized to reduce the impact on communication performance caused by increased propagation loss from the use of millimeter-wave band. Controlling the beam in the direction of the sensor leads to increased received signal levels, resulting in high-reliable communications. The beamforming in the ESPER antenna, which element arrangement is similar to the proposed antenna, is achieved by exciting only one element and terminating the other elements with load impedances in order to act as a radiator or reflector, similar to a Yagi-Uda array antenna. Unlike the ESPER antenna, the elements on the circle of the proposed antenna are employed as excitation elements during the AOA estimation. Therefore, those are also used as excitation elements to create a beam toward the direction of the sensor. With regard to a phased array antenna, the received signals of each element are combined with a phase difference to achieve in-phase excitation in a desired direction, which yields a strong radiation gain. When isotropic point sources are used in the proposed antenna, the weight functions can be uniquely determined by the geometric phase difference between the antennas. However, when dipole antennas are applied, the directivity of each element changes from omnidirectional due to the electromagnetic mutual coupling, so it is necessary to find the optimal weight functions, which depend on the distorted directivity. The weight functions are determined in such a way that the gain in the communication direction of the combined radiation pattern yields a maximum value [31]. All elements are phase-shifted by \(\tau_{i}\) to be in the in-phase state at the angle of the incoming wave in consideration of the electromagnetic mutual coupling. Furthermore, the amplitude of the excitation voltage of each element, \(w_{i}\), is controlled according to the radiation gain in each element at the angle of the incoming wave. As the four elements form a circular arrangement with \(90^{\circ}\) intervals, the beam can be rotated every \(90^{\circ}\) in the azimuth plane by applying the same weight function. Moreover, by taking advantage of the symmetry feature of the circular array, the beam direction should be considered in the range of 0 to \(45^{\circ}\). Table 1 summarizes the optimal weight functions in all elements of the proposed antenna for creating the beam toward the azimuth angle \(\phi\). In Table 1, the weight \(w_{i}\) is normalized by the maximum value, and the phase shift \(\tau_{i}\) is based on the element with the greatest weight. The directivity of each element, which is utilized in the search for the optimal weight function, is calculated using the method of moments. All dipole antennas are terminated with 50 \(\Omega\). Figure 11 shows the \(\theta\)-polarized radiation beam based on Table 1 in the _xy_-plane as a function of the angle of the incoming wave. The black arrows in the figure indicate the angle of the incoming wave. The red arrows are the full width at half maximum of the radiation gain. As can be seen from Figure 11, the beam can be formed in the desired direction and produce a radiation gain of about 7 dBd (9 dBi) at the angle of the incoming wave, which results in a large SNR. This maximum radiation gain is greater than that reported in the literature [32]. Moreover, a full width at half maximum of \(60^{\circ}\) or more can be observed, so a high radiation gain can be expected in all directions by beam steering according to the estimated angle of the incoming wave.