A Miniaturized Broadband 1-Bit Coding Reconfigurable Intelligent Surface for NLOS UE Localization and Uplink Communication

In this paper, a broadband 1-bit coding metasurface-based reconfigurable intelligent surface (RIS) is presented. The unit cell of the metasurface consists of a wide dipole modified with interdigital capacitors and loaded with an SMP 1340-040LF PIN diode. The proposed element offers cell miniaturization and a stable angular response. A phase difference of 180$\degree \pm$ 30$\degree$ is achieved for a frequency range of 4.85-6.05 GHz between the ON and OFF states for the normal incidence of the TE polarized wave, whereas it provides a fairly stable response with reflection loss of less than 3 dB and phase difference of 180$\degree$ $\pm$ 50$\degree$ for oblique incidence up to 45$\degree$. The RF is isolated from the DC on the bias lines using properly designed butterfly-shaped radial stubs. Using this unit cell, a prototype with an array of 16 $\times$ 10 elements is constructed. A low-cost microcontroller-based control circuit is designed, which can be plugged-in for biasing the PIN diodes of such array. The theoretically calculated and full-wave simulated radiation patterns of the array are validated using experiments inside anechoic chamber. Furthermore, the capability of the RIS for non-line of sight (NLOS) user equipment (UE) localization and robust uplink communication is demonstrated using LTE communication framework. This shows great potential of our RIS for applications, such as in unmanned aerial vehicle (UAV) localization and its uplink communication at NLOS or extended range.

Advancements in Terahertz Antenna Design

The promising way to provide sufficient transmission capacity is by accessing transmission bands at higher carrier frequencies. This desire for higher carrier frequency or more bandwidth led the researchers to take advantage of the terahertz (THz) spectrum. The opportunity for large bandwidth in the THz band leads to the possibility of easy, high data rate transmission. In spite of the advantages, the THz band suffers from large free space path loss. In the development of THz communication systems, the antenna is the most significant component. The focus is especially on designing highly directive antennas because they enhance the performance of the overall system by compensating for the large path loss at THz and thus improving the signal-to-noise ratio. This chapter presents different types of THz antennas, including planar, reflectarray, horn antenna, and lens antenna. Emphasis has been made to present the latest trend of designing THz antennas using carbon-based materials, such as graphene and carbon nanotubes. The performance of these antennas has been compared with that of traditional copper-based THz antennas by critically analyzing their properties. A brief discussion on THz power sources is included in this chapter for completeness. A comprehensive discussion on different fabrication techniques has been provided to appraise the reader of the general fabrication processes of THz components.