Researchers from Southeast University in China, along with collaborators from other institutions, have developed a novel amplifying and filtering reconfigurable intelligent surface (AF-RIS) designed to significantly improve wireless relay systems. This advancement, published in Engineering, aims to address key challenges in 6G networks by enhancing signal strength, improving frequency selectivity, and reducing hardware costs and power consumption.

The study introduces an AF-RIS that integrates amplifying and filtering capabilities into a reconfigurable intelligent surface. Traditional reconfigurable intelligent surfaces (RISs) have shown promise in manipulating electromagnetic waves to optimize wireless communication channels. However, they often suffer from limitations such as limited operational range and spectral interference. The AF-RIS overcomes these issues by providing in-band signal energy enhancement and out-of-band signal filtering, thereby achieving array miniaturization and improved anti-interference capabilities.

The AF-RIS design features a meticulously crafted 4×8 array that incorporates power dividing and combining networks. This architecture reduces the number of amplifiers and filters required, leading to significant decreases in hardware costs and power consumption. Each AF-RIS element is equipped with 2-bit phase control, which significantly improves the array’s beamforming performance. The experimental results demonstrate the AF-RIS’s powerful capabilities in beam-steering, frequency selectivity, and signal amplification.

The research highlights the AF-RIS’s ability to dynamically control electromagnetic wave characteristics, including amplitude, phase, polarization, frequency, and wavevector. This is achieved through the integration of tunable elements such as positive–intrinsic–negative (PIN) diodes and varactor diodes, which can be controlled via a micro-control unit (MCU) or field-programmable gate array (FPGA). The AF-RIS exhibits an in-band energy enhancement of over 20 dB compared to a lossy RIS of the same size. This substantial gain allows for the miniaturization of RIS arrays while maintaining sufficient signal strength.

Furthermore, the AF-RIS demonstrates robust out-of-band rejection performance, crucial for minimizing spectral interference in increasingly congested frequency bands. The study shows that the AF-RIS maintains a stable and excellent filtering effect across different beam-steering angles and control voltages. This is quantitatively measured using parameters such as the Q-factor and the rectangle coefficient K_20dB, both of which indicate sharp transitions at the ends of the reflection curve.

In practical wireless communication experiments, the AF-RIS was tested using a software-defined radio (SDR) platform. The results confirmed the AF-RIS’s ability to enhance signal energy, improve communication quality, and provide superior frequency selectivity. The system exhibited notable improvements in signal-to-noise ratio (SNR) and video transmission quality when compared to traditional lossy RISs.

The development of the AF-RIS represents a significant step towards realizing the potential of RIS technology in next-generation wireless communication systems. By combining amplifying and filtering functionalities with dynamic beam-steering capabilities, the AF-RIS offers a practical solution for expanding signal coverage, reducing spectral congestion, and optimizing RIS array deployment. This technology is expected to play a pivotal role in shaping the future of 6G networks, providing a foundation for efficient and high-performance wireless communication.

The paper “A Wideband Amplifying and Filtering Reconfigurable Intelligent Surface for Wireless Relay,” is authored by Lijie Wu, Qun Yan Zhou, Jun Yan Dai, Siran Wang, Junwei Zhang, Zhen Jie Qi, Hanqing Yang, Ruizhe Jiang, Zheng Xing Wang, Huidong Li, Zhen Zhang, Jiang Luo, Qiang Cheng, Tie Jun Cui. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.06.015. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.