## 4 Results
#### 4.3.2 Correlation Between Rectifiers and Performance Metrics
Microwave rectifiers, while maintaining a similar average frequency (\(\approx\)2.5 GHz), display a narrow distribution with high-end outliers, indicating a design orientation toward higher-frequency operation with minimal variability--an attractive feature for high-frequency applications such as millimeter-wave sensing or compact wireless power transfer systems. Taken together, the results suggest that rectifier topology influences not only conversion performance but also spectral behavior. Configurations like Schottky, multi-step, single-step, and microwave rectifiers demonstrate stable frequency profiles that align well with systems requiring tight spectral control. In contrast, absence of a rectifier stage corresponds to greater variability, making such configurations less suitable for frequency-sensitive applications. * Gain vs. rectifier  
This subsection explores the relationship between rectifier topology and antenna gain in RF energy harvesting systems. Although gain is primarily influenced by antenna geometry and operating frequency, rectifier design can impact the overall system's electromagnetic behavior through impedance matching and loading effects. Certain rectifier configurations may be better suited to preserve or enhance directional performance, depending on their integration characteristics and coupling strategies. By analyzing the distribution of gain across different rectifier types, this section aims to identify patterns that inform design choices where both energy conversion and signal reception efficiency are critical. Figure 23 shows the distribution of antenna gain across different rectifier configurations, revealing distinct patterns that reflect both design characteristics and application constraints. Schottky rectifiers exhibit a mean gain of approximately 5 dBi with a narrow distribution, indicating low variability and consistent directional performance. This makes them particularly suitable for applications that prioritize stable and predictable gain, such as low-power wireless communication systems. Similarly, Half-wave rectifiers demon  
Figure 22: Boxplot showing frequency distribution of different rectifier designs for energy harvesting. strate a comparable mean gain (\(\approx\)5 dBi) and a tight distribution with minor low outliers, reinforcing their suitability for systems where gain uniformity is essential. Single-step rectifiers present a median gain also near 5 dBi, though with occasional negative outliers, suggesting a generally stable behavior with limited high-end performance. These rectifiers may be preferred in scenarios where gain consistency is required, even if absolute values remain modest. In contrast, multi-step rectifiers show a slightly lower average gain (\(\approx\)4 dBi) and a broader distribution with significant positive and negative outliers. This high variability implies that, while high gain may be achieved in some configurations, the system's performance is more sensitive to implementation details--necessitating robust design strategies to mitigate signal loss. Full-wave rectifiers display a mean gain of around 3 dBi and a wide distribution, reflecting substantial variability. Such variability suggests the potential for both high and low performance depending on conditions, again requiring careful system-level optimization. Microwave rectifiers are characterized by the lowest average gain (\(\approx\)2 dBi) and the narrowest distribution, pointing to very low variability and consistent but limited directional capability. This configuration is best suited for space-constrained applications where gain uniformity is prioritized over amplification strength. Systems without a clearly defined rectifier show the highest mean gain (\(\approx\)6 dBi) but also the broadest distribution, indicating high variability and inconsistent performance. While these systems may yield high gain under favorable conditions, they lack the predictability required in applications demanding controlled and reliable reception.