title: Development of terahertz antennas for 6G wireless communication
Creators: name: Zubair, Muhammad
Publisher: name: University of Glasgow
Year: 2024

description: The world is rapidly advancing towards next-generation wireless communication systems. A significant advancement is a use of millimeter-wave (mmWave) technology in 5G, which addresses the spectrum shortage in current 4G cellular systems operating below 6 GHz. However, the increasing number of emerging applications such as virtual reality (VR), the Internet of Things (IoT), and autonomous vehicles, along with future applications yet to be conceived such as remote surgery, will require even greater data rates and lower latency than what 5G networks currently offer. Consequently, the development of sixth-generation (6G) wireless communication systems becomes crucial to meet these needs for higher bandwidth, increased data rates, ultra-low latency, enhanced throughput, and massive connectivity.

To overcome these challenges, the utilization of the terahertz (THz) band, which lies between the microwave and infrared regions of the electromagnetic spectrum, is being explored. The terahertz frequency range, spanning from 0.1 THz to 10 THz, is considered a viable solution for advancing next-generation wireless communication, THz imaging and sensing applications, as well as for future technologies beyond 5G and sixth-generation (6G). The THz spectrum offers a largely underutilized bandwidth with low spectral congestion. However, its effectiveness is hindered by significant path loss and high signal attenuation due to oxygen absorption, posing additional challenges in developing highly efficient wideband, high-gain, compact, and cost-effective antenna solutions with precise microfabrication techniques.

Traditional antenna design methods, which are based on analytical and numerical techniques, often face limitations in addressing the complexities associated with terahertz frequencies. These methods can be computationally intensive, time-consuming, and may not always yield optimal solutions, especially when dealing with complex geometries and non-conventional materials. This work investigates the feasibility of AI-driven antenna design techniques, specifically the Surrogate Model-assisted Differential Evolution for antenna synthesis (SADEA) series. In this series SADEA-I, and the latest installment of self-adaptive Bayesian neural networks surrogate-model-assisted differential evolution for antenna optimization (SB-SADEA), have been employed for the first time (to the best of our knowledge) to achieve optimal performance.

This thesis encompasses four high-performance THz antenna design solutions offering, aimed at next-generation THz wireless applications and 6G technologies. The first THz antenna design is a high-gain, compact, wide-bandwidth 4-element planar antenna array based on a hybrid corporate network. The array has dimensions of 1.82 λ0 × 1.79λ0 × 0.044 λ0, where λ0 is the free space wavelength at 105 GHz. It offers a-10 dB impedance bandwidth across the entire 100-110 GHz range, a low side lobe level, total efficiency above 80%, and a peak measured gain of 13.90 dBi with less than 1 dBi gain variation across the whole band (100-110 GHz). This makes it an ideal candidate for radar systems, as a broad 1 dB gain bandwidth antenna can enhance target detection and tracking accuracy, thereby improving situational awareness in surveillance applications. Additionally, the wide frequency coverage provided by the 1 dB gain bandwidth antenna ensures versatility for a variety of applications requiring robust and reliable wireless communication capabilities.

The second antenna design uses a parasitic patch element approach in serial feed to create a compact, cost-effective, planar 5-element array with high gain. The design provides, and enhances co-polarized currents, resulting in an increase in gain from 13.15 dBi to 16.50 dBi and aperture efficiency from 9.18% to 20.47% with the same antenna aperture size. It achieves high directional beams towards the broadside over 10 GHz (100-110 GHz), with a radiation efficiency exceeding 92.4% and a peak realized gain of about 16.50 dBi, with minimal gain variation (less than 0.90 dB) across the entire band. This makes it a suitable candidate for THz wireless access communication scenarios that require large bandwidth and multi-gigabit data rate, such as high-definition video signal transfer. An antenna with a broad 1 dB gain bandwidth can find various applications across different sectors. Notably, it could be particularly effective in THz indoor wireless communication systems where reliable and high-speed data transmission is crucial.

Thethird and fourth proposed solutions involve a novel THz structure featuring a 64-element array with a hybrid corporate-series feed network, fabricated using advanced microfabrication techniques such as electron beam lithography (E-beam). The integration of microfabricated THz antenna arrays with coplanar waveguide (CPW) feed techniques significantly enhances antenna performance, improving bandwidth, gain, efficiency, and ease of fabrication. This design offers ultra-wideband (UWB) performance with a-10 dB impedance bandwidth across the entire frequency range from 0.75 to 1.1 THz. The proposed arrays exhibit a peak gain of 15.05 dBi, consistent over the entire operating frequency range with a gain variation of less than 1.5 dB. Additionally, the antenna achieves a peak total efficiency of 87.78%. The high performance of these microfabricated THz antenna arrays makes them suitable for various applications, such as THz communication systems, imaging, and spectroscopy. The use of CPW feed techniques also allows for easy integration with other components in THz systems, further enhancing their versatility and practicality.

The primary goal of this study is to design, fabricate and measure novel THz antennas using AI-driven design techniques for 6G wireless communications. By successfully designing, fabricating, and measuring various novel THz antennas with different materials, this research paves the way for future short-range THz wireless communication.