Antennas and Microwave Circuits

“Lightweight Broadband Circularly Polarized Stacked Patch Antenna Formed by Meshed Aluminum Disks for Inter-Satellite Communication” presents a lightweight, broadband, circularly polarized, all-metal antenna designed for LEO-to-GEO inter-satellite links. The antenna utilizes four aluminum disks, selected for their high thermal conductivity and low density. The broadband performance, achieving a 33.81% bandwidth, arises from interlayer coupling between the disks and the crucial 90 phase difference between adjacent radial stubs. Stacked disks, supported by spacers and posts, enhance mechanical strength, mitigating vibration and stress. Furthermore, the unique meshed disk design achieves a 54.06% weight reduction while maintaining mechanical robustness, resulting in a total weight of only 30 grams. 

Researcher: Hsiu-Ping Liao (廖修平)

The mmWave antenna module, designed for 30-300 GHz wireless communication, supports 5G, satellite links, autonomous radar, and IoT applications. In this project, in collaboration with ASUS, we designed a dual-band, dual-polarized mmWave array antenna specifically for 5G mobile frequency bands (24.25 GHz–29.5 GHz and 37 GHz–43.5 GHz). By employing beamforming technology in conjunction with a codebook, the design enhances signal gain and directivity, effectively mitigating the significant path loss associated with high-frequency transmission. With the ongoing advancement of mmWave technology, future antenna modules are expected to evolve toward higher performance, smaller form factors, and greater integration to meet the demands of emerging applications. 

Researcher: Sheng-Yeh Yang (楊昇曄) and Bing-Jia Chen (陳秉嘉)

A novel circularly polarized (CP) leaky-wave antenna based on half-mode substrate-integrated waveguide is proposed. This design incorporates unit cells featuring transverse slots, longitudinal slits, and capacitors, enabling frequency-based CP beam scanning from −42° to 35° while maintaining an axial ratio (AR) below 3 dB. By integrating varactor diodes, the antenna achieves fixed-frequency CP beam scanning through reverse bias voltage control. Simulated and measured results demonstrate a scanning range of −30° to 32° with |S11| < −10 dB, peak gain of 10.4 dBic, and 65% efficiency. Its compact size and stable performance make it well-suited for radar systems that necessitate fixed-frequency CP beam scanning. 

Researcher: Kuan-Hsun Mao (毛冠勛) and Sheng-Wei Wu (吳聖偉)

“Miniaturized Microstrip-Based Phase Inverter as a Phase Delay Component at 24 GHz” presents a miniaturized microstrip phase inverter (PI) based phase delay component operating from 23.1 to 25 GHz. The proposed mini-PI integrates interdigital capacitors and meander slots within the ground plane while utilizing only two metallic vias to achieve a compact footprint. The circuit area of the layout is reduced to only 25% compared to a conventional meander line. Simulated and measured results demonstrate an 8.04% usable bandwidth, 0.53-dB average insertion loss, and phase deviation within ±10° from 23.1 to 25 GHz. This design offers promising size reduction and competitive performance, making it suitable for high-density microwave circuit integration.

Researcher: Sheng-Wei Wu (吳聖偉)

Polarization reconfigurable antenna elements are crucial for satellite communications (SATCOM) and radar systems. In SATCOM, their polarization agility mitigates multipath effects and ensures accurate polarization alignment, significantly enhancing signal quality. For radar applications, the ability to switch between different polarizations improves target detection and characterization. This research presents a single-feed antenna design capable of electronically switching between left-handed and right-handed circular polarization. By meticulously designing the DC routing network to minimize its impact on the original boundary conditions, the design achieves polarization agility while maintaining a wide axial-ratio bandwidth, optimizing performance across diverse applications. 

Researcher: Yun-Ting Tsai (蔡昀廷)

This ASUS-NTU collaboration project aims to automate antenna design to enhance efficiency, reduce costs, and optimize performance. Traditional methods rely on optimization algorithms coupled with computationally expensive electromagnetic simulators. To accelerate the design process, we are exploring surrogate-based optimization (SBO), where machine learning models replace computationally expensive electromagnetic solvers. While effective, SBO can become computationally demanding for large-scale or high-dimensional problems. To address this limitation, we have also developed state-of-the-art topology optimization methods utilizing adjoint fields. These methods enable efficient handling of complex designs. Both approaches can be applied independently or combined, offering a versatile and innovative solution for next-generation antenna design challenges. 

Researcher: Wei-Cheng Chen (陳韋丞)