Novel Antenna Role in the Integration of ISAC for 6G Wireless Communications

A novel antenna has been developed by a research group co-led by a researcher at the City University of Hong Kong (CityU).

A significant feature of the new-generation antenna is that the direction, frequency, and amplitude of the radiated beam from the antenna can be changed through space-time coding software control. Image Credit: City University of Hong Kong.

This enables manipulation of the frequency, direction, and amplitude of the radiated beam and is anticipated to play a significant role in the union of sensing and communications (ISAC) for 6th-generation (6G) wireless communications.

Once the fabrication is done, the structure and characteristics of conventional antennas cannot be altered. However, the frequency, direction, and amplitude of the electromagnetic waves coming from this new-generation antenna, which is known as a “sideband-free space-time-coding (STC) metasurface antenna,” could be altered via space-time coding (that is, software control), allowing great user flexibility.

The central part of this groundbreaking feature is that the response of the metasurface (artificial, thin-sheet material with sub-wavelength thickness and made up of various sub-wavelength meta-atoms) could be altered by shifting the meta-atoms present on its surface between radiating and non-radiating states. This includes turning on and off switches by regulating the electric current.

This enables the STC metasurface antenna to identify complicated wave manipulation in the space and frequency domains via software control and to make a highly directed beam and the desired radiation pattern.

Professor Chan Chi-hou, Acting Provost and Chair Professor of Electronic Engineering in the Department of Electrical Engineering at CityU, who headed the research, stressed that the antenna depends on the successful combination of two research progresses, specifically amplitude-modulated (AM) leaky-wave antennas and space-time coding methods.

Dr. Wu Gengbo, a postdoctoral fellow in the State Key Laboratory of Terahertz and Millimeter Waves (SKLTMW) at CityU, initially suggested the new idea of AM leaky-wave antennas in 2020 in his Ph.D. studies at CityU.

The concept provides an analytical approach to synthesize antennas with the desired radiation patterns for different specific uses by simply changing the antennas’ shape and structure,” explained Dr. Wu.

However, as with other antennas, once the AM leaky-wave antenna has been fabricated, its radiation characteristics are established. At that time, Dr. Dai Junyan, from a research group headed by Academician Cui Tiejun and Professor Cheng Qiang, from Southeast University in Nanjing, China, who introduced STC technologies, collaborated with Professor Chan’s group at CityU.

Dr Dai’s expertise in space-time coding and digital metasurfaces to dynamically reconfigure antenna performance added a new, important dimension to the antenna research at the SKLTMW,” said Professor Chan, who is also Director of the SKLTMW at CityU.

Furthermore, the time modulation of electromagnetic waves present on metasurfaces generally produces undesirable harmonic frequencies, known as sidebands. Such sidebands tend to carry one portion of the radiated electromagnetic wave energy and meddle with the beneficial communication channels of the antenna, resulting in “spectrum pollution.”

However, Professor Chan and his team suggested a novel design, which utilizes a waveguide (a line for sending electromagnetic waves by consecutive reflection from the inner wall) and successfully repressed the unwanted harmonics. This helps them obtain a high-directivity beam and allows safe communication.

With the AM leaky-wave antenna and space-time coding technologies, we achieve the designated radiation characteristics by controlling the on-off sequences and duration of the ‘switches’ on the antenna through software.

Chi Hou Chan, Professor, Department of Electrical Engineering, City University of Hong Kong

Dr. Wu added, “A high-directivity beam can be generated with the new antenna, allowing a wide range of radiation performance without having to redesign the antenna, except for using different STC inputs.”

The energy gets emitted from the radiated beam of the STC metasurface antenna could be concentrated to a focal point with fixed or altering focal lengths. This can be utilized for real-time imaging and further treated as a kind of radar to scan the surroundings and feedback data.

The invention plays an important role in the ISAC for 6G wireless communications. For example, the radiated beam can scan a person and create an image of the person, allowing mobile phone users to talk to each other with 3D hologram imaging. It also performs better against eavesdropping than the conventional transmitter architecture.

Chi Hou Chan, Professor, Department of Electrical Engineering, City University of Hong Kong

The co-first authors of the study are Dr. Wu and Dr. Dai, and the corresponding authors are Dr. Dai, Professor Cheng, Academician Cui, and Professor Chan.

Without the collaboration and complementary expertise of the two research teams at CityU and Southeast University, we could not have achieved these research results. We hope that the new-generation antenna technology will become more mature in the future and that it can be applied to smaller integrated circuits at lower cost and in a wider range of applications.

Chi Hou Chan, Professor, Department of Electrical Engineering, City University of Hong Kong

The study of the CityU team was financially supported by the Hong Kong Research Grants Council, under the Theme-Based Research Scheme, and the Guangdong-Hong Kong Joint Laboratory for Big Data Imaging and Communication.

Journal Reference:

Wu, G-B., et al. (2022) Sideband-free space–time-coding metasurface antennas. Nature Electronics.


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