A novel octahedron frequency reconfigurable multiband antenna for microwave sensing-based IoT applications is proposed in this work. This reconfigurable antenna operates over the bands 1.57–2.15 GHz, 2.13–3.0 GHz, 3.17–3.43 GHz, 5.2–5.8 GHz, 6.3–6.78 GHz, 8.31–8.90 GHz, 9.04–9.58 GHz and 12.03–13.14 GHz which can be used for wireless sensing, space and IoT applications. By using omega shape slot in the radiating structure and with PIN diodes switching to change the current direction, the desired resonant frequencies are achieved. The PIN diodes are controlled by using an IoT device NodeMcu. As per the software programmed, the NodeMcu switches the PIN diodes into ON and OFF conditions. We can change the program and monitor through the World Wide Web. The s-parameter characteristics and the radiation patterns have been measured, and good compatibility between simulated and measured results has been identified. The designed model is tested with CDAC Cmote device and controlled through IoT for data transmission and reception at desired operating bands.

Reconfigurable Intelligent Surfaces (RIS) have become a trending technology with the potential to meet the demand for high data rates and extended signal coverage in mmWave (millimeter wave) and terahertz wireless communications. RIS consists of a planar array of reconfigurable Metasurface unit cells with controllable reflection characteristics to the incident wave. This RIS surface is considered a passive element because it doesn’t consume any power to radiate signal. These RISs offer an energy-efficient alternative to massive MIMO, enabling beamforming, polarization conversion, and beam steering operations. This chapter focused on the fundamentals of RIS, applications to wireless communications, and challenges in RIS design with research directions. A design case study using a numerical simulation tool is presented to understand RIS’s design and analysis. A unique RIS unit cell geometry, utilizing AlGaAs (Aluminium Gallium Arsenide) pin diode is presented in this chapter to get a full insight into the design and simulation methodology. The design and analysis of the RIS unit cell are included, along with simulated results obtained using CST numerical simulation software. A comprehensive analysis of the optimized unit cell and its functionality is demonstrated in this chapter. The design and analysis of a RIS unit cell at mmWave frequencies is the subject of this chapter. In addition to the RIS design aspects, we compare its performance with existing mmWave RIS structures. Finally, the future directions in RIS design are discussed that pave the way to explore the potential of RIS in futuristic 5G/6G communications, such as signal coverage and energy efficiency. Hence, this chapter provides a full insight into fundamentals, an overview of applications, and a design and analysis of the RIS surface to satisfy the enlarged signal coverage and the demand for futuristic wireless communications. <!----> <!----> <!----> <!---->