# A Review of Multifunctional Antenna Designs for Internet of Things
## 1 Introduction  
Around the world, technology is advancing at a pace that surpasses anything previous generations could have imagined. Today, wireless communication has transformed from a privileged good to a necessary need in developed countries. To further increase the quality of life, a trend has emerged that exploits mobile communication protocols to interconnect more and more devices [1]. For this revolution to materialize, there is a need to establish a way to ensure that everything is connected to everything else. The Internet of Things (IoT) encapsulates this vision by integrating a diverse range of systems. Some popular examples include intelligent homes, industrial applications, advanced farming techniques, urban innovations, and the smart energy grid [2]. The IoT is an extensive network that connects a wide array of devices, enabling them to exchange data with one another at relatively high speeds [2]. For this vast network to function, these devices must incorporate some form of communication system, whether wired or wireless. Wired communication is generally preferred due to its high data transfer rates, low latency, reliability in packet delivery, and efficient power consumption. However, the necessity of physical connections makes it impractical for many applications, limiting its appeal. On the other hand, wireless communication offers flexibility and adaptability, allowing devices to be placed in various environments without the need for complex installation procedures. The goal is to make it available anywhere and at any time. Despite these advantages, wireless communication faces reliability issues. The quality of a wireless linkbetween two devices can be influenced by several factors, including range, environmental conditions (such as humidity and proximity to the ground), interference, and more. These factors can lead to increased data loss, jamming, connection drops, high latency, and even loss of control over the devices [2]. Therefore, there is a pressing need to develop more reliable and efficient wireless communication methods while also minimizing the power consumption of the devices involved. The wireless connection of two devices involves communication via electromagnetic (EM) waves that can be divided into two major categories: optical and microwave links. Optical systems utilize EM waves in the infrared or visible light spectrum, enabling high data transmission rates. However, optical communication is primarily limited to line-of-sight (LoS) applications because light cannot penetrate obstacles like walls and can be disrupted by weather and environmental conditions. In contrast, microwaves, while they are relatively immune to weather and environmental conditions, allow the penetration of signals through various objects, facilitating non-line-of-sight (non-LoS) communication. Within microwave systems, antennas play a crucial role in wireless communication. Antennas are capable of emitting or receiving EM waves from their radiating surface, efficiently converting them to or from electrical currents, thereby enabling the exchange of information over distances without the need for physical connections. Designing antennas for IoT applications presents unique challenges due to the diverse requirements of each application field (such as vehicle-to-vehicle communications (V2V), biomedical implants, smart sensors, etc.). A versatile antenna designed for IoT purposes must tackle several objectives, including easy deployment, minimal physical size, and the capability to efficiently receive a wideband response. Often, these demands are met by designing antennas that are omnidirectional or quasi-isotropic and support multiple polarizations, often in the form of printed antennas [3], especially for smart home applications. Depending on the specific application, more specialized antenna types may be necessary.