The development of 5G networks is paving the way for future generations of wireless technology, which envisions the use of higher frequency bands (terahertz range, above 100 GHz) and the proliferation of smart, interconnected devices (Internet of Things, IoT). Realizing this requires antennas with specific properties: high gain and directionality to overcome path loss at terahertz frequencies, while also being adaptable to various geometries for widespread deployment. Conformal antennas, which conform to the shape of an object, are suitable for this, as demonstrated in aerospace communications. However, legacy systems using longer wavelengths often result in antennas too large for IoT devices. The need for conformal antennas operating in the terahertz range is therefore crucial. This research presents an original study of conformal terahertz antennas based on the leaky-wave antenna architecture, known for its adaptability to non-planar geometries and wide bandwidth potential. The implementation uses an air-filled parallel-plate metal waveguide, bent into a cylindrical shape with an azimuthal slot aperture, allowing guided waves to leak as they propagate. This configuration creates three distinct operational regimes defined by the interplay of wavelength, curvature radius, and slot aperture length. The study will explore the physics of these regimes, compare model calculations to experimental results, and demonstrate the use of conformal terahertz antennas as multi-beam high-gain transmitters in data transmission experiments.

Previous research extensively explores leaky-wave antennas at both radio frequencies (RF) and terahertz (THz) frequencies, highlighting their usefulness in various applications. Studies have shown the leaky-wave waveguide's adaptability to non-planar geometries and its ability to be easily engineered to explore a wide range of parameters. Prior work on conformal antennas has focused on lower frequencies, where longer wavelengths often lead to larger antenna sizes unsuitable for many IoT applications. The use of conformal antennas in aerospace has been widely documented, emphasizing the importance of size, weight, and aerodynamic considerations. However, these systems cannot support the data rates envisioned for future terahertz networks. Research on THz leaky-wave antennas has primarily focused on planar structures. This research addresses the gap in understanding the behavior of conformal leaky-wave antennas operating in the THz range and their potential for high-data rate, wideband communication in diverse physical environments.

The study begins by analyzing an air-filled curved parallel-plate waveguide. A finite difference scheme is used to solve the Helmholtz equation for the geometry, resulting in an eigenequation (Equation 1). The effective refractive index of the guided mode is calculated as a function of curvature, revealing a relationship that asymptotically approaches the planar value as the radius increases (Equation 2). A geometrical optics interpretation is used to explain the frequency-dependent critical radius separating the planar-like and curved propagation regimes (Equation 4). Experimental verification of the model is performed using the cut-back technique and THz time-domain spectroscopy to measure the effective refractive index (Equation 5). The impact of curvature on waveguide dispersion is investigated, specifically calculating the group velocity dispersion (GVD) (Equation 6) and its impact on the maximum achievable bitrate (Equation 8). The study then analyzes far-field radiation from a leaky-wave antenna with a narrow slot in the outer plate. The radiated electric field is computed using the Stratton-Chu diffraction integral (Equation 9), simplified for a narrow slot (Equations 11-13). The model's accuracy is validated using finite-element method simulations. Experimental radiation patterns are measured using a THz time-domain spectroscopy system and a Schottky diode. Two conformal leaky-wave antennas are fabricated with different radii of curvature, and their radiation patterns are compared to model predictions. Finally, a multi-beam conformal antenna is demonstrated, using on-off keying (OOK) modulation at 1 Gbps to transmit data. Bit error rates are measured to assess the communication performance.

The study reveals two distinct propagation regimes in curved parallel-plate waveguides: a planar TE₁-like mode for large radii and a whispering-gallery-like mode for small radii. The curvature significantly impacts the effective refractive index and group velocity dispersion (GVD), especially at lower frequencies and tighter bends. A semi-analytical model accurately predicts the effective refractive index and radiation patterns, even at larger curvature radii, showing that changes in the radiation pattern are attributed to the changing wave vector angle during propagation. Even for relatively large radii, the directivity decreases due to the changing wave vector. The experimental results show excellent agreement with the model predictions, validating the proposed approach. The multi-beam antenna successfully generates two directional beams with angular separation as designed, demonstrating the feasibility of conformal leaky-wave antennas for achieving wide angular coverage while maintaining low bit error rates (<10⁻⁵). These results highlight the potential of conformal THz leaky-wave antennas for multi-beam high-gain transmission in wireless communication systems.

The findings demonstrate the feasibility and effectiveness of conformal leaky-wave antennas at terahertz frequencies for high-data rate wireless communication. The study successfully bridges the gap between theoretical modeling and experimental validation, providing a comprehensive understanding of the antenna's behavior under different curvature conditions. The ability to generate multiple high-gain beams with low bit error rates significantly improves angular coverage and expands the potential applications of THz technology, particularly for IoT networks. The detailed analysis of dispersion provides critical insights into the design considerations for high-bandwidth applications. The successful demonstration of data transmission using OOK modulation confirms the practical relevance of the proposed antenna design for real-world wireless communication scenarios. The results contribute significantly to the advancement of THz wireless communication and antenna technologies.

This research provides a comprehensive understanding of conformal leaky-wave antennas at THz frequencies. The developed semi-analytical model accurately predicts the behavior of these antennas under various curvature conditions. The experimental verification of the model, including data transmission with low bit error rates, demonstrates the practical feasibility of these antennas for achieving multi-beam high-gain transmission. Future research could explore more complex antenna geometries, different slot designs for optimized leakage characteristics, and integration with advanced modulation schemes to further enhance communication performance in terahertz systems.

The study primarily focuses on a specific type of conformal antenna geometry (cylindrical parallel-plate waveguide with a rectangular slot). The applicability of the findings to other antenna shapes might need further investigation. The analysis of dispersion focuses primarily on the impact of curvature, with limited consideration of other factors that could influence dispersion, such as material properties and waveguide imperfections. The experimental setup uses a specific modulation scheme (OOK), and further analysis is needed to explore the antenna's performance under other modulation techniques.