[Paper Review] Terahertz Dielectric Resonator Antenna Coupled to Graphene Plasmonic Dipole

Seyed Ehsan Hosseininejad, Mohammad Neshat+6 more|arXiv (Cornell University)|Jan 11, 2018

Plasmonic and Surface Plasmon Research22 references18 citations

TL;DR

This paper proposes a terahertz dielectric resonator antenna (DRA) coupled to a graphene plasmonic dipole to enhance gain and radiation efficiency. By leveraging hybrid plasmonic-dielectric mode coupling via a multilayer PMMA-GaAs-Graphene structure, the DRA excites higher-order modes (e.g., $TE_y^{112}$) at 2.4 THz, achieving 7 dBi gain and 70% radiation efficiency—6.5 dB higher than the standalone graphene dipole with minimal area overhead.

ABSTRACT

This paper presents an efficient approach for exciting a dielectric resonator antenna (DRA) in the terahertz frequencies by means of a graphene plasmonic dipole. Design and analysis are performed in two steps. First, the propagation properties of hybrid plasmonic onedimensional and two-dimensional structures are obtained by using transfer matrix theory and the finite-element method. The coupling amount between the plasmonic graphene mode and the dielectric wave mode is explored based on different parameters. These results, together with DRA and plasmonic antenna theory, are then used to design a DRA antenna that supports the $TE_{y}^{112}$ mode at 2.4 THz and achieves a gain (IEEE) of up to 7 dBi and a radiation efficiency of up 70%. This gain is 6.5 dB higher than that of the graphene dipole alone and achieved with a moderate area overhead, demonstrating the value of the proposed structure.

Motivation & Objective

• Address the low gain and radiation efficiency of graphene plasmonic antennas in the terahertz band due to high propagation losses.
• Overcome the limitations of purely plasmonic antennas by integrating a dielectric resonator antenna (DRA) to enhance directivity and efficiency.
• Explore hybrid plasmonic-dielectric waveguide structures to enable strong coupling between graphene plasmonic modes and DRA modes.
• Design a compact, reconfigurable THz antenna with high gain and low area overhead for nanoscale and high-data-rate applications.
• Demonstrate that exciting higher-order DRA modes (e.g., $TE_y^{112}$) significantly improves performance compared to fundamental modes or standalone plasmonic dipoles.

Proposed method

• Model one-dimensional and two-dimensional hybrid plasmonic structures using transfer matrix theory and finite-element method to analyze mode propagation and coupling.
• Use the approximate formula $f_{ ext{res}} \approx \frac{c}{2n_{\text{eff}}L}$ to design the graphene plasmonic dipole for optimal resonance at 2.4 THz.
• Design the DRA using the formula $f_{\text{res}} \approx \frac{c}{2n_{\text{eff}}L}$ to excite $TE_y^{111}$ and $TE_y^{112}$ modes at target frequencies.
• Implement a multilayer structure: five-layer graphene on PMMA (L-layer) over GaAs (H-layer) substrate, with a rectangular DRA above.
• Feed the dipole via a center gap with a photoconductive source, and simulate full-wave electromagnetic response using full-wave solvers.
• Optimize the DRA height ($d_H$) and graphene chemical potential ($\mu_c$) to maximize coupling and radiation efficiency.

Experimental results

Research questions

• RQ1 How does the coupling strength between graphene plasmonic modes and dielectric resonator modes vary with H-layer thickness and chemical potential?
• RQ2 Can higher-order DRA modes ($TE_y^{112}$) be effectively excited and utilized to enhance gain in a graphene-plasmonic antenna system?
• RQ3 What is the impact of hybrid plasmonic-dielectric waveguide design on radiation efficiency and directivity in the terahertz band?
• RQ4 How does the gain and efficiency of the coupled DRA-graphene system compare to a standalone graphene plasmonic dipole?
• RQ5 To what extent can the area overhead be minimized while achieving significant performance gains in THz antenna design?

Key findings

• The $TE_y^{112}$-mode DRA coupled to a graphene plasmonic dipole achieves a gain of 7 dBi at 2.4 THz with 70% radiation efficiency.
• The proposed antenna design improves gain by 6.5 dB compared to the standalone graphene dipole, which achieves only 0.5 dBi gain.
• The radiation pattern of the $TE_y^{112}$-mode DRA is more directive than that of the $TE_y^{111}$-mode DRA, indicating enhanced directivity.
• Impedance oscillations above 2.5 THz in hybrid antennas are attributed to excitation of higher-order DRA modes such as $TE_y^{113}$ at 3.3 THz.
• The H-field distribution confirms simultaneous excitation of the $TE_y^{111}$ mode in the DRA and the open-circuit (OC) resonance in the graphene dipole at 2.4 THz.
• The $TE_y^{112}$ mode resonance at 2.8 THz is confirmed by both simulation and theoretical modeling, validating the design approach.