## 5 Results and Discussion  
The rectifier, shown in Figure 6, was simulated over a range of input RF powers (\(-25\) dBm to \(20\) dBm) to evaluate its performance regarding output voltage, efficiency, and power. As shown in Figures 10 and 11, both output voltage and efficiency at a \(50\) Ohm load increased consistently with rising RF input. Specifically, the output voltage started at \(0.2\) V at \(-5\) dBm and peaked at \(1.8\) V at \(20\) dBm. Notably, meaningful output power and current were observed only for RF inputs exceeding \(5\) dBm, peaking at \(27\) mA and \(45\) mW at \(20\) dBm (Figures 10 and 11). However, the generated power remains insufficient for IoT devices, prompting the exploration of alternative architectures to enhance the rectifier's output capabilities. Additionally, Figure 11 illustrates that the rectifier achieves an efficiency of \(20\%\) at \(-5\) dBm, increasing to a maximum of \(52\%\). The RF-EH, single antenna, and rectifier were evaluated across a range of load resistances (50\(-\)1000 ohms) and input RF power levels (Figures 12 and 13). As load resistance increased, both efficiency and output voltage generally improved. At an input power of 20 dBm, the output voltage rose significantly for resistances up to 450 ohms, peaking at 6.5 V at 1 kohm. Meanwhile, the efficiency gradually increased with load resistance at all input RF power level values, reaching a maximum of 83% for 450 ohms and 20 dBm (Figure 13). For load resistances above 450 ohms at 20 dBm, efficiency declined because the output voltage increased only slightly compared to the increase in load resistance, while the input power remained constant. Figure 11: The rectifier’s output power measured at the node (Vdc) (refer to Figure 6) and efficiency for different input RF power levels. Figure 10: The proposed rectifier’s output voltage measured at the node (Vdc), shown in Figure 6, and current at different input RF power levels. Various MIMO configurations, ranging from 2 to 16 antennas, were explored to enhance power output for IoT devices. Simulation results (Figures 14-16) demonstrate a steady increase in output voltage, current, and power as the number of antennas increases. Figure 14 shows that MIMO systems can generate output voltage even at \(-10\) dBm input power; practical voltage is achieved only at higher RF input levels. At 20 dBm, the maximum voltages recorded are 6.3 V, 4.5 V, 3.2 V, 2.4 V, and 1.8 V for MIMO configurations with 16, 8, 4, 2, and 1 antennas. Notably, all MIMO setups at low RF input exhibit reduced output, highlighting inadequacy for IoT power requirements. This is due to power dissipation across rectifier diodes, a challenge mitigated by employing diodes with low voltage drop or utilising cascade rectifiers. Figure 12: The output voltage of a single-antenna RF energy harvester across various loads and diverse levels of RF input power. Figure 13: The efficiency of a single–antenna RF energy harvester under different loads and RF input power levels. Figure 16: The MIMO RF-EH output current at varying input RF power levels. Figure 14: The MIMO RF-EH output voltage at various RF input power levels. Figure 15: The output power of the MIMO RF-EH at different RF input power. The MIMO designs' efficiency is assessed using (5) and (9). Figure 17 depicts the system's efficiency, indicating a notable rise in the growing antenna count. Efficiency exceeds 95% at higher input power levels, showcasing the system's effectiveness. Moreover, it underscores that increasing the number of antennas improves efficiency for low inputs. The output voltage, current, and power of the 16-antenna MIMO RF-EH, as depicted in Figures 14-16, peak at 6.1 V, 108 mA, and 649 mW. This highlights the system's ability to power IoT devices under high RF input conditions. However, alternative energy sources are necessary for low RF input scenarios. The I-V and P-V simulation results conducted in ADS and MATLAB are depicted in Figure 18 and Figure 8, respectively.