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Enabling FR2-5G Communication with Dielectric OAM Transmitarrays

Miguel Á. Balmaseda-Márquez, Juan E. Galeote-Cazorla, Álvaro Liébana-Bolívar, Alejandro Ramírez-Arroyo, Carlos Molero Jiménez, J. F. Valenzuela-Valdés

Abstract

This paper investigates the potential of near-field (NF) indoor communications in the FR2 frequency bands using fully dielectric structures to generate orbital angular momentum (OAM) waves. All-dielectric platforms based on distributions of T-shaped unit cells are employed for this purpose. The unit cell design is based on a circuital approach and analytical formulations, where phase shifts necessary for OAM generation are achieved by varying the dielectric-to-air ratio within the structure. Based on this unit cell, a set of transmitarrays (TAs) are designed to produce specific OAM modes. These TAs are fabricated in-house using stereolithographic 3D printing and experimentally tested. The tests evaluate two key features of OAM beams: the orthogonality of distinct vortex modes, as characterized by their electric field distributions, and their object-avoidance capability, enabled by the central null characteristic of the wavefront. In addition, a field-test within an indoor environment is conducted emulating a real wireless system. A bit error rate lower than 10\textsuperscript{$-$6} is observed for solidary modes in Tx and Rx, whereas orthogonal modes produces an increment in 4 order of magnitude. The obtained results reveals that the prototype is suitable for short-range scenarios, enabling techniques such as OAM-multiplexation or physical-layer security thanks to the effective orthogonality beteween modes.

Enabling FR2-5G Communication with Dielectric OAM Transmitarrays

Abstract

This paper investigates the potential of near-field (NF) indoor communications in the FR2 frequency bands using fully dielectric structures to generate orbital angular momentum (OAM) waves. All-dielectric platforms based on distributions of T-shaped unit cells are employed for this purpose. The unit cell design is based on a circuital approach and analytical formulations, where phase shifts necessary for OAM generation are achieved by varying the dielectric-to-air ratio within the structure. Based on this unit cell, a set of transmitarrays (TAs) are designed to produce specific OAM modes. These TAs are fabricated in-house using stereolithographic 3D printing and experimentally tested. The tests evaluate two key features of OAM beams: the orthogonality of distinct vortex modes, as characterized by their electric field distributions, and their object-avoidance capability, enabled by the central null characteristic of the wavefront. In addition, a field-test within an indoor environment is conducted emulating a real wireless system. A bit error rate lower than 10\textsuperscript{6} is observed for solidary modes in Tx and Rx, whereas orthogonal modes produces an increment in 4 order of magnitude. The obtained results reveals that the prototype is suitable for short-range scenarios, enabling techniques such as OAM-multiplexation or physical-layer security thanks to the effective orthogonality beteween modes.
Paper Structure (10 sections, 6 equations, 12 figures, 4 tables)

This paper contains 10 sections, 6 equations, 12 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Characterization of the unit cell. Circuit model
  3. Circuit-model validation. Single and stacked T-blocks
  4. Design of fully dielectric TAs for OAM-waves generation
  5. Validation of the TAs and experimental tests for communication links
  6. Characterization of the TAs
  7. Experimental validation of OAM orthogonality
  8. Self-healing and object avoidance
  9. Field-test of OAM-based communications
  10. Conclusion

Figures (12)

  • Figure 1: Indoor scenario with a emitting TA with a multimodal frequency range for OAM communications. Through only one emitter it is possible to transmit several modes to a high number of objectives.
  • Figure 2: (a) Front view of the T-shaped unit cell (b) Perspective view of the unit cell. Blue color corresponds to air and the brown color to the dielectric material (c) Circuital equivalent model for a T-shaped unit cell of length $l$.
  • Figure 3: Simulations to study the oblique incidence (TE and TM incidence) for a T-shaped cell with a $\chi = 0.45$. (a) Transmission coefficient for $\varepsilon_{\text{r}}=2.6$ (b) Transmission coefficient for $\varepsilon_{\text{r}}=8$.
  • Figure 4: (a) Unit cell formed by 4 different concatenated T-blocks. Periodicity $p = 2.7\,$mm. (b) Equivalent circuit for the concatenated T-blocks whose parameters be seen in Table \ref{['table_values']}.
  • Figure 5: Scattering parameters for the cascade of several cells (a) Magnitude of the transmission coefficient (b) Phase of the transmission coefficient.
  • ...and 7 more figures