## 4 Results
#### 4.1.2 Correlation Between Antenna Geometry and Performance Metrics
Despite their inherent geometric complexity, fractal antennas consistently demonstrate a moderate mean area (\(\approx\)2000 mm\({}^{2}\)). Nonetheless, their area distribution displays significant variability, which may be attributed to the scale-dependent characteristics of their design. Bow-tie antennas, conversely, present a comparable mean area (\(\approx\)2500 mm\({}^{2}\)) coupled with relatively limited variability. It is worth noting, however, that specific configurations can exhibit extended upper bounds, implying occasional demands for expanded footprints. Overall, the results highlight a trade-off between compactness and performance flexibility, with certain designs offering predictable spatial constraints, while others--especially those in the \"other\" category--reflect experimental or application-specific adaptations that may prioritize functional gains over spatial efficiency. * Efficiency vs. antenna design  
To further investigate antenna geometry's influence on system performance, this section examines radiation efficiency distribution across various antenna design categories. The boxplot analysis assesses the variability and central tendencies of efficiency values for each design type, offering insight into how structural characteristics may impact energy conversion capabilities in rectenna-based harvesting systems. The analysis presented in Figure 6 reveals distinct patterns in radiation efficiency across evaluated antenna designs. Array antennas exhibit a mean efficiency of approximately 68%, accompanied by a relatively wide distribution and a low lower bound, indicating considerable variability and potential for low-efficiency outcomes in certain configurations. Rectangular antennas demonstrate a similar trend, with a mean efficiency of around 60% and a broad distribution that extends to values as low as 5%, suggesting significant performance dispersion. Circular antennas show a mean efficiency of roughly 55%, with a distribution comparable to the rectangular type but slightly narrower at both extremes, indicating moderate variability and a tendency toward lower efficiency values. Bow-tie antennas, in contrast, display a narrow distribution centered around a mean of 60%, reflecting low variability and generally stable performance near the average. Designs grouped under the \"other\" category exhibit a mean efficiency close to 55%, but with a wide distribution and a notably low lower bound. This signals high variability  
Figure 6: Boxplot showing efficiency distribution of different antenna designs for energy harvesting. and the possibility of both very low and relatively high efficiencies, depending on specific structure. Slot antennas average around 60% efficiency, showing a tight distribution with outliers on both the lower and upper ends, suggesting stable performance punctuated by occasional deviations. Spiral antennas stand out with the highest mean efficiency (\(\approx\)96%) and an extremely narrow distribution, indicating both low variability and consistently high performance. Similarly, fractal antennas exhibit a mean efficiency of approximately 80%, accompanied by a tight and elevated distribution, reinforcing their potential for delivering high efficiency with minimal performance fluctuation. * Operation frequency vs. antenna design  
This subsection explores the relationship between antenna design and operating frequency, a critical parameter in the performance of energy harvesting systems. By employing boxplot analysis, frequency distributions associated with each antenna type are examined, enabling the identification of typical operating ranges, design-specific trends, and potential trade-offs between geometry and spectral behavior. This analysis provides valuable insight into the suitability of different antenna structures for specific frequency bands used in ambient RF energy harvesting. The analysis of operating frequency distributions, as shown in Figure 7, highlights notable differences across antenna designs.