# Smart Gateway for Healthcare Networks Based on Beam Steering Technology
## 3 Directivity Measurements
### Beam Steering Function  
In the AOA estimation function of the proposed antenna, since the weights for \(E_{\Delta}\), which indicate the mixing ratio of each element, are the same value, a generalized equal power combiner is sufficient. However, for the beam steering function, the weight \(w_{i}\) of each element is different, as shown in Table 1, so an unequal power combiner is needed to create the beam. In this paper, we unavoidably conducted a preliminary experiment for evaluating the radiation pattern of the beam steering function by using an equal power combiner. The development of a five-way unequal power combiner circuit, such as a two-way combiner [35], will be a subject for our future studies. Figure 15 illustrates the configuration of the beamforming network. The unequal power combiner, which is needed to embody the weight functions, is substituted with the available equal power combiner and attenuators. Furthermore, the phase shift is achieved by using differing lengths of fabricated coaxial cables that connect with the antenna. To the best of our knowledge, a five-way equal power combiner has not been commercially available so far. Thus, we used a six-way equal power combiner/divider (mini circuit, ZN6 PD-63W-S+) for the experiments. Applying this results in a power loss due to one wasted port, which is loaded at 50 \(\Omega\). In addition, the attenuators required to make non-uniform weighting also generate serious power losses. To evaluate the beam of the proposed antenna, the total input power of the antennas must be calibrated while considering the power losses in the power combiner/divider, attenuators, and coaxial cables. Otherwise, the proposed antenna performance would be underestimated compared to the analytical outcomes. In our previous study, a calibration method to achieve Gaussian angular power spectra in a three-dimensional OTA apparatus was proposed [36]. The calibration of the beamforming for the proposed antenna is an extension of that method. Figure 15: Configuration of a beamforming network. The principle of the calibration method is explained while considering it to be a transmitting antenna based on the reciprocal theorem. To obtain the reference gain for the directivity measurement, the average received power \(E\Big{[}\big{|}S_{21}\big{|}^{2}\Big{]}\) of the half-wavelength dipole antenna in the full-azimuth angle was measured in an anechoic chamber. Then, the reference level \(REF\) is calculated using \(E\Big{[}\big{|}S_{21}\big{|}^{2}\Big{]}\) based on the following equation:  
\[REF=\frac{E\Big{[}\big{|}S_{21}\big{|}^{2}\Big{]}}{G} \tag{11}\]  
where \(G\) is the ratio of the input power \(P_{in}\) of the beamforming network to the output power \(P_{out}\) of the proposed antenna. The output power of the proposed antenna constructed by the five dipole antennas is calculated as follows:  
\[P_{out}=P_{1}+P_{2}+P_{3}+P_{4}+P_{5} \tag{12}\]  
where \(P_{i}\) indicates the output power of each element and is calculated, considering the power loss of each component, by the following equation:  
\[P_{i}=P_{in}PL_{PDi}PL_{ATTi}PL_{Ci} \tag{13}\]  
where \(PL_{PDi}\) denotes the ratio of the input to the output power of the equal power combiner/divider, which value is ideally one-sixth. However, the measured value \(PL_{PDi}\) is small due to the power losses that occur in the device. \(PL_{ATTi}\) is the insertion loss of the attenuator, whereas \(PL_{Ci}\) is the power loss of the coaxial cable. The attenuator is utilized to represent the weight \(w_{i}\) mentioned in Section 2.3. The weight is defined by the voltage, which is converted to power-based value by squaring. Thereby, the attenuator of each element can be set as listed in Table 2. It should be noted that the attenuator is set up in 0.5 dB increments, considering that it has negligible effect on the beam to be formed. The setting of the attenuators is applied to the directivity measurements in the anechoic chamber, and the propagation experiments in an indoor situation are described in Section 5.