## 4 Results
#### 4.1.2 Correlation Between Antenna Geometry and Performance Metrics  
To deepen the understanding of how antenna design influences system performance, this subsection analyzes the relationship between geometric and electromagnetic parameters--such as area, efficiency, operating frequency, and gain--across the different antenna categories identified previously. A series of box plot visualizations is employed \begin{table}
\begin{tabular}{c c c c c} \hline
**Ref.** & **Frequency (GHz)** & **BW (MHz)** & **Substrate** & **Thickness (mm)** \\ \hline
[47] & 0.868 & 13.5, 14.3 & Not conventional & — \\ \hline
[90] & 0.9, 1.17 & — & FR4 & 1.6 \\ \hline
[62] & 0.868, 0.92–0.96, 1.8 & 500, 680 & FR4 & 1.6 \\ \hline
[34] & 0.915, 2.45, 0.45 & — & FR4, not conventional & 1.57, 0.76, 1.6 \\ \hline
[56] & 0.4 & 165 & RT Duroid 5880 & 0.8 \\ \hline
[69] & 1.8 & — & FR4 & 1.6 \\ \hline
[93] & 0.82 & 2700 & Textil & 0.2 \\ \hline
[98] & 2.4, 12.6 & — & Not conventional & 3 \\ \hline
[33] & 2.4 & 400 & Not conventional & 0.5 \\ \hline \end{tabular}
\end{table} 
Table 12: Construction characteristics of antennas within the other geometry classification. Resonant frequencies, bandwidth at each frequency, substrate used, and antenna width are included. to highlight statistical trends and variations within each design type, enabling comparative insights into performance trade-offs relevant to energy harvesting applications. This methodological approach has been previously reported and validated in related literature, where similar analyses were used to extract meaningful patterns across antenna configurations [109]. * Area vs. antenna design  
Antenna geometry's influence on occupied surface area is a critical factor in energy harvesting applications, particularly given space constraints and integration demands with other system components. Figure 5 illustrates antenna area distribution across various design categories via boxplot analysis. This visualization facilitates a comparative assessment of spatial requirements, revealing variability within each design and highlighting designs such as array and circular antennas with a wider range of occupied area, in contrast to more compact configurations like spiral and fractal geometries. In all boxplot visualizations, the yellow horizontal line denotes the distribution mean value, whereas the central line within the box indicates the median. This convention is used consistently across all boxplot figures presented in the study. Figure 5 shows the distribution of occupied surface area for various antenna designs commonly employed in energy harvesting systems. Analysis reveals marked differences in spatial requirements and variability across design categories. Array antennas, for instance, exhibit a moderate mean area (\(\approx\)2000 mm\({}^{2}\)) but also show substantial dispersion and the presence of high outliers, suggesting that while many configurations remain compact, certain implementations can demand significantly larger surfaces. Rectangular and slot antennas display comparable mean values (around 2000-2500 mm\({}^{2}\)) but differ in variability: rectangular designs tend to be more consistent, whereas slot antennas exhibit broader distributions and higher outliers, indicating less predictable area requirements. Circular and spiral antennas both present relatively small mean areas (\(\approx\)1000 mm\({}^{2}\)), but differ in statistical dispersion. Circular designs show higher variability due to outliers, while spiral antennas are characterized by a narrow distribution, reflecting consistent compactness. Conversely, antennas categorized under \"other\" display the largest mean  
Figure 5: Boxplot showing the area distribution of different antenna designs for energy harvesting. area (\(\approx\)7000 mm\({}^{2}\)) and a wide interquartile range. This is expected given the heterogeneous nature of this group, which encompasses unconventional and hybrid geometries.