## 4 Results
#### 4.1.1 Antenna Architectures for Energy Harvesting  
Figure 3 shows reference designs of different types of antennas identified in the documents. Each of these antenna designs offers unique strengths, and the key to optimizing performance lies in selecting the right type for specific application. Whether it is the efficiency and compactness of fractal antennas or the precise beam control of array antennas that is needed, choosing the appropriate design ensures that the energy harvesting system can meet its operational goals effectively. From the reviewed literature, the percentage distribution of each analyzed antenna type was determined, as shown in Figure 4. The results reveal that rectangular patch  
Figure 3: Types of antenna designs, including array antennas (**a**), bow-tie (**b**), circular patch (**c**), spiral (**d**), slot insertion (**e**), rectangular patch (**f**), array antenna and (**g**) fractal. Each design has unique characteristics related to energy harvesting applications. These are representative figures of antennas, which are intended as a visual reference for the design type but not necessarily functional with the current dimensions. antennas are the most extensively studied, with a significantly larger representation in the literature compared to other antenna types. Furthermore, Table 4 provides a comprehensive classification of the articles dedicated to different antenna designs. This analysis highlights the prominence of rectangular patch antennas while recognizing the diversity of antenna types explored for energy harvesting applications. To provide a more detailed description of the identified antenna types, each design is briefly outlined below. * Rectangular
Rectangular patch antennas remain a staple in wireless communication. Their low profile and ease of manufacturing, combined with an omnidirectional radiation pattern, make them a popular choice across various industries, particularly in mobile and IoT applications, as summarized in Table 5.  
[PERSON] et al. [58] and [PERSON] et al. [89] focus on dual-band rectangular antennas, highlighting their capacity for efficient RF energy capture across two distinct frequency ranges. These designs emphasize optimization's role in improving energy conversion and are presented as highly effective solutions for sustainable energy harvesting. Similarly, \begin{table}
\begin{tabular}{l l} \hline \multicolumn{1}{c}{**Geometric Design**} & \multicolumn{1}{c}{**References**} \\ \hline Rectangular patch & [31,32,36,45,50,52,54,58,59,68,71,75,78,81,82,86,87,89,92,94,97,100,106] \\ \hline Array & [37,39,49,53,57,60,63,65,66,80,83,84,88,91] \\ \hline Slot insertion & [30,43,44,48,61,67,70,72,73,85,99,108] \\ \hline Circular patch & [38,51,74,76,79,101,103-105,107] \\ \hline Spiral & [35,42,55,90,95,96] \\ \hline Bow-tie & [41,64,77] \\ \hline Fractal & [29,40,46,102] \\ \hline Other & [33,34,47,56,62,69,93,98] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Article classification by geometry design. Figure 4: Percentage distribution of reviewed bibliography according to antenna type analyzed. [PERSON] et al. [62] introduce a dual-band rectenna with a dual-mode metallic rim design, which enhances signal capture in both bands, offering greater adaptability and flexibility for RF energy harvesting. For applications demanding broader spectral coverage, [PERSON] et al. [45], [PERSON] et al. [94], and [PERSON] et al. [82] propose triple-band rectangular antennas. [PERSON] et al. 's [45] stepped design demonstrates exceptional versatility and improved efficiency, making it suitable for scenarios requiring a wide frequency range. [PERSON] et al. [82] further enhance this concept with a single-layer rectenna capable of triple-band operation, optimized for outdoor energy harvesting applications. [PERSON] et al. [94] contribute a triple-band microstrip-based rectenna, showcasing its ability to efficiently convert RF energy into usable electrical power across multiple bands.