# A Review of Multifunctional Antenna Designs for Internet of Things
## 2 Materials and Methods
### Smart Home Appliances
#### 2.2.4 Recent Feedback on Smart Homes  
In Table 2, the characteristics of various IoT antennas for smart home applications are displayed. Different methodologies have been implemented to ensure multi-polarization-capable antennas while maintaining small footprints. One group of antennas capable of integrating into the smallest devices operates in the millimeter-wave spectrum, using either cavities or frequency-selective surfaces to increase their directivity (gain) and form narrow-beamwidth main lobes in the radiation pattern. Cavity-backed antennas are a solution for the next generation of IoT devices, offering higher data rates due to their large bandwidth, compact structures, and increased efficiency. However, this feature is not always desirable in smart home applications because IoT devices must communicate with different \"Things\" that may be placed in arbitrary directions. Highly directive antennas require a beamforming network to ensure a reliable link between nearby devices. Various solutions to this problem have been partially proposed in different works [78; 79; 80; 81; 82], but we are quite far from establishing a holistic, commercially ready cavity-backed antenna along with its feeding network. In addition, cavity-backed antennas operate at millimeter range preferably in the ISM band, but currently, there is only one below 100 GHz (24.1 GHz). The previously presented millimeter antennas do not belong in that band, meaning that more research is needed towards exploiting this specific band for smart home communications. Therefore, we believe that in the coming years more researchers will propose novel electronically reconfigurable compact beamforming networks for smart home appliances. In this direction, metasurfaces and frequency-selective surfaces [83; 84; 85; 86; 87] can either enhance the beam-steering capabilities of the antenna or enable multi-polarization reception, albeit with the drawback of increasing the volume of the structure. In the sub-6 GHz region, implementing a cavity-backed or metasurface antenna array is challenging due to the longer wavelengths in this band, making them unsuitable for small IoT devices. As explained previously, a quasi-isotropic radiation pattern is a more realistic option to meet this requirement. As depicted in Table 2, most radiation patterns show a main front lobe with almost no back lobe due to the ground plane. Therefore, there is a need for multi-polarization antennas with nearly isotropic radiation patterns. In this context, monopole antennas [88; 89; 90; 91; 92] exhibit omnidirectional or quasi-isotropic radiation patterns and operate in multiple bands [90]. They can also be printed on flexible substrates to wrap around any IoT device [56; 92]. The smart home industry has already attracted major companies and seems too large to be driven solely by individual efforts. However, many innovative devices and antennas are initially inspired, developed, and published by university researchers. These innovations are then often modified and exploited by industry research and development departments. Consequently, smart home research evolves slowly and lacks a clear direction, which is often unfair to university researchers who do not fully benefit from their creations. To address this issue, a framework for collaboration between businesses and universities is needed.