## 4 Results
#### 4.1.3 Influence of Substrate Materials on Antenna Behavior
RT Duroid substrates show a slightly higher median near 2.5 GHz, accompanied by reduced variability, indicating improved stability and reliability for systems operating at moderately high frequencies. Rogers substrates demonstrate consistent behavior centered around a median frequency of 3 GHz, with minimal dispersion and outliers. This performance profile makes Rogers a dependable choice for low-to-mid-frequency applications where consistent spectral response is essential. In contrast, non-conventional substrates exhibit the broadest frequency range, with a median near 2.5 GHz and upper outliers reaching up to 8 GHz. Figure 11: Boxplot showing efficiency distribution of different substrates for energy harvesting. Textile substrates operate at lower frequencies, with a median below 3 GHz and a limited spread. While this constrains their use in high-frequency applications, their mechanical flexibility and integration potential make them well-suited for wearable and conformal systems, where structural adaptability takes precedence over spectral performance. Overall, substrate selection proves to be a critical determinant of frequency behavior, guiding design choices based on application-specific spectral requirements and fabrication constraints. * Gain vs. antenna substrate  
This subsection analyzes how antenna gain varies with respect to substrate material used in design and fabrication. Gain is a critical parameter in energy harvesting systems, as it determines an antenna's ability to concentrate received power in a given direction. Substrate characteristics--such as dielectric constant, loss tangent, and mechanical stability--directly affect radiation patterns and power efficiency. By examining the statistical distribution of gain across different substrate types, this section aims to identify material-dependent trends and assess their implications for directional performance and application-specific antenna optimization. Gain analysis across different substrate materials, as depicted in Figure 13, reveals distinct performance trends that reflect the interplay between material properties and radiation behavior. FR4 substrates present a median gain of approximately 5 dBi, but with a broad distribution, ranging from -15 dBi to over 15 dBi. This wide variability suggests a strong dependence on antenna geometry and design factors, positioning FR4 as a viable option for cost-effective applications where gain performance is less critical or where tuning flexibility is acceptable. RT Duroid exhibits a narrower gain distribution centered around a median of 4 dBi, indicating more consistent and reliable performance. This stability makes it particularly suitable for designs that require moderate, yet dependable, gain characteristics. Rogers substrates show a slightly lower median gain, near 3 dBi, with reduced variability overall, although the presence of some dispersed values indicates occasional deviations. Despite this, Rogers remains a strong candidate for high-precision applications where dimensional stability and electromagnetic consistency are prioritized. Figure 12: Boxplot showing frequency distribution of different substrates for energy harvesting. Non-conventional substrates exhibit a similar median gain (\(\approx\)3 dBi) with limited variability and a few scattered outliers. This behavior suggests their appropriateness in specialized or experimental configurations where gain is not the dominant design criterion. In contrast, textile substrates display the lowest median gain, around 2 dBi, combined with noticeable dispersion. While their gain performance is limited, their mechanical flexibility and conformability make them ideal for wearable and structurally adaptive applications where electromagnetic efficiency is secondary to integration capability. * Comparative insights Analysis of antenna substrates reveals that material selection significantly impacts the occupied area, radiation efficiency, operating frequency, and gain, offering distinct advantages for various applications.