Sending All the Right Signals

Wi-Fi 7, 6G cellular networks, terahertz communication — these are some of the things that come to mind when we think of cutting-edge and emerging wireless communications technologies. The supporting hardware, like antennas, usually takes a backseat in our minds. Yet without properly engineered antennas, none of these methods of communication would be possible. And that would have a cascading effect that impacts applications in areas ranging from IoT to edge AI.

Fortunately, some people are giving antenna design the attention that it deserves. Researchers at the City University of Hong Kong have developed an innovative antenna that might prove to be capable of handling the communications challenges of tomorrow. Whereas traditional antennas have fixed properties that limit their capabilities, the team’s novel antenna is adaptable, and can control multiple frequency components, which makes it possible to do things like significantly increase channel capacity and transmit multiple signals in different directions.

There are a number of methods currently being investigated to enable flexible frequency control. However, current methods — such as nonlinear bulk media and electro-optic modulators — suffer from limitations in spectral controllability, complexity, and inefficiencies. Factors like these have largely prevented these technologies from being used in real-world applications.

The researchers recognized that metasurfaces might offer a more practical solution. These materials are capable of providing precise control over electromagnetic waves, but existing designs face challenges in independent manipulation of harmonic orders and efficiency.

To overcome these issues, a clever design was developed. The new antenna is a waveguide-integrated metasurface that incorporates a synthetic moving-envelope approach to enable advanced frequency control. The metasurface uses spatiotemporal modulation, leveraging time as an additional degree of freedom to manipulate electromagnetic waves. The design involves meta-atoms with 1-bit ON-OFF digital switching, which creates the synthetic moving-envelope structure. This structure consists of superimposed fundamental sinusoidal moving envelopes, each corresponding to a specific harmonic frequency.

By controlling these envelopes, the antenna can simultaneously generate and independently regulate multiple harmonic orders, including their wave properties and power distribution. The integration of positive-intrinsic-negative diodes ensures high precision in frequency manipulation and suppression of unwanted harmonics, leading to cleaner signal outputs.

Functionally, the antenna can perform complex tasks like unidirectional frequency conversion, frequency comb generation, and frequency-division multiplexing, making it highly versatile for applications in wireless communications, spectroscopy, and quantum systems. The waveguide integration ensures efficient transformation of guided waves into free-space radiation while minimizing interference from undesired harmonics.

Given the broad potential impact of the technology, the researchers hope their work will spawn further innovations involving metamaterials and metasurfaces. For more on the latest in antenna technology, be sure to check out this shape-shifting antenna that takes flexibility to a new level!