# 5G/B5G Internet of Things MIMO Antenna Design
## 3 Simulation and Measurement Results and Discussions  
The proposed MIMO antenna is simulated using a high frequency structured simulator (HFSS). The design was fabricated and tested at the University of Queensland, Australia. A photograph of the fabricated prototype is provided in Figure 2. A DC-40 GHz 2.92 mm connector was assembled, with each antenna feeding via soldering for measurement purposes. Figure 5 shows the measurement setup used in an anechoic chamber for radiation and gain patterns. Figure 4: The 3D radiation patterns of the proposed MIMO antenna at (**a**) 28 GHz and (**b**) 3.6 GHz. Figure 5: The proposed MIMO antenna design installed inside an anechoic chamber in the antenna measurement lab. The simulated S-parameter curves for Ant. 1, Ant. 2, Ant. 3, and Ant. 4 are shown in Figure 5(a), while the measured S-parameter curves for Ant. 1, Ant. 2, Ant. 3, and Ant. 4 are shown in Figure 5(b). These results are plotted for the Sub-6 GHz band. It can be seen that the proposed MIMO antenna (S\({}_{11}\), S\({}_{22}\), S\({}_{33}\), and S\({}_{44}\)) operates at 3.6 GHz. An impedance matching bandwidth of approximately 300 MHz with \(-10\) dB impedance matching is achieved in the simulation and measured versions. A slight shift in measurements is observed, attributable to the fabrication and measurement tolerances. Isolation in both simulated and measured versions is more than 17 dB in the whole operated band. See Figure 5(a) for S\({}_{12}\) (Ant. 1 and Ant. 2), S\({}_{13}\) (Ant. 1 and Ant. 3), and S\({}_{24}\) (Ant. 1 and Ant. 2). The simulated and measured S-parameter curves for Ant. 1, Ant. 2, Ant. 3, and Ant. 4 for mm-wave bands are shown in Figure 6(a),b. Both the simulated and measured results show good agreement. All the antenna elements (S\({}_{11}\), S\({}_{22}\), S\({}_{33}\), and S\({}_{44}\)) show \(-10\) dB impedance matching from 25 GHz to 29 GHz. A slight discrepancy in the measured curves, especially for Ant. 3, is attributable to fabrication and measurement tolerances. The isolation in the mm-wave band is more than 30 dB between all antennas (Ant. 1 to Ant. 4). The normalized simulated and measured 2D radiation patterns, in terms of gain for Ant. 1, Ant. 2, Ant. 3, and Ant. 4 at 3.6 GHz, are shown in Figure 8. The simulated plots follow the measured plot trend, showing good agreement. Each plot has a directional radiational pattern with wider beamwidth, illustrating the MIMO pattern diversity performances. Figure 6: S-parameter curves for Ant. 1 to Ant. 4 at 5G Sub-6 GHz band: (**a**) simulated and (**b**) measured. Figure 7: S-parameter curves for Ant. 1 to Ant. 4 at 5G mm-wave band: (**a**) simulated and (**b**) measured. The normalized simulated and measured 2D radiation patterns, in terms of gain for Ant. 1, Ant. 2, Ant. 3, and Ant. 4 at 28 GHz, are shown in Figure 9. The simulated plots follow the measured plot trend, showing good agreement. Each plot has a more directional radiational pattern with a narrow beamwidth, compared to the 3.6 GHz band. This is an advantage, because more directive antennas are needed at the mm-wave band to compensate for higher path loss. The results also indicate that MIMO radiation pattern diversity performances are at the mm-wave band. As shown in Figure 8, at \(\theta=90^{\circ}\) (X-Y plane), the main beam of Ant. 1 is pointing (i.e., the propagating direction of the signal) in the \(x\)-direction (\(\varphi=180^{\circ}\)); Ant. 2 is pointing in the \(x\)-direction (\(\varphi=0^{\circ}\)); Ant. 3 is pointing in the \(y\)-direction (\(\varphi=-90^{\circ}\)); and Ant. 4 is pointing in the \(y\)-direction (\(\varphi=90^{\circ}\)), covering most of the azimuth plane (X-Y plane) of special coverage. The peak simulated and measured realized gain of each antenna is more than 3.5 dBi in the whole covered band at Sub-6 GHz band, as shown in Figure 10a. While, the peak simulated and measured realized gain of each antenna is more than 8 dBi in the whole covered band at mm-wave, as shown in Figure 10b.