## 4 Results
#### 4.1.1 Antenna Architectures for Energy Harvesting
[PERSON], [PERSON], [PERSON], and [PERSON] [67] propose a dual-band planar rectenna designed for RF energy harvesting in Universal Mobile Telecommunication Service (UMTS) bands. The core contribution of this work lies in its antenna, which is a slot-type antenna. This particular slot geometry is key to achieving dual-band behavior and optimizing impedance matching, a critical aspect for maximizing the rectenna's conversion efficiency. [PERSON] and [PERSON] [85] present a self-adaptive rectenna designed for RF energy harvesting applications. The key receiving element is a slotted rectangular patch antenna with a partial ground plane, optimized for operation at 2.45 GHz. This antenna is engineered to capture ambient RF energy, and its performance is fundamental to overall system efficiency. The antenna's design, coupled with the implementation of a rectifier circuit, allows maintaining high RF-to-DC conversion efficiency across a wide range of input power levels. [PERSON] et al. [72] present a compact and efficient dual-port microstrip rectenna designed for wireless RF energy harvesting in the LTE band. Their innovation primarily lies in the antenna, which incorporates two ports and features a complex geometry with arrow-shaped, circular, and rectangular slots. This multifaceted antenna design is crucial for its ability to efficiently capture RF energy in the LTE band while facilitating a dual-port connection. This configuration not only optimizes energy harvesting but also allows for better matching between antenna and rectifier circuit. * Circular Circular  
Circular antennas serve a different niche. Their ability to handle circular polarization allows them to efficiently interact with circular waves, a crucial requirement in satellite communication, as detailed in Table 8.  
In the study presented by [PERSON] et al. [103], a circular antenna with a printed split-ring resonator is developed, achieving circular polarization. Specifically designed for energy harvesting, this antenna effectively captures radio frequency energy under circular polarization conditions. The results highlight its efficiency in RF energy capture, positioning it as a promising alternative for power harvesting applications. Similarly, [PERSON] et al. [107] focus on designing a circular antenna that features omnidirectional reception and dual polarization, enabling efficient energy capture from multiple directions. This study optimizes RF energy harvesting capabilities under diverse conditions and angles, making it particularly suitable for energy harvesting in dynamic environments. [PERSON] et al. [74] present research focused on developing a metasurface designed for efficient electromagnetic energy capture. This metasurface is distinguished by its ability to receive signals from a wide range of incidence angles, making it especially suitable for energy harvesting under diverse conditions and directions. The study results highlight its high efficiency in electromagnetic energy capture. On another front, [PERSON] et al. [79] introduce the design of a circular textile rectenna notable for its low profile and ability to capture energy omnidirectionally with dual polarization. This rectenna has achieved over 50% efficiency, positioning it as an ideal solution for wearable applications where power sources are limited. These findings underscore this innovation's effectiveness in high-efficiency energy capture, significantly contributing to portable device autonomy. [PERSON] et al. [38] present a circular design characterized by its modularity, flexibility, lightness, and ability to integrate an energy harvesting system. The research focuses on developing a versatile RFID tag, adaptable to various applications and wearable environments. The authors highlight this tag's efficiency in radiofrequency energy capture, as well as its flexible and lightweight operation. [PERSON] et al.