New Antenna Uses Saltwater and Plastic to Steer Radio Beams

A new antenna that uses saltwater and plastic instead of metal to shape radio signals could make it easier to build networks that use VHF and UHF signals.

Being able to focus the energy of a radio signal towards a given receiver means you can increase the range and efficiency of transmissions. If you know the location of the receiver, and are sure that it’s going to stay put, you can simply use an antenna that is shaped to emit energy mostly in one direction and point it. But if the receiver’s location is uncertain, or if it’s moving, or if you’d like to switch to a different receiver, then things get tricky. In this case, engineers often fall back on a technique called beam-steering or beamforming, and doing it at at a large scale is one of the key underlying mechanisms behind the rollout of 5G networks.

Beam-steering lets you adjust the focus of antenna without having to move it around to point in different directions. It involves adjusting the relative phases of a set of radio waves at the antenna: these waves interfere constructively and destructively, cancelling out in unwanted directions and reinforcing the signal in the direction you want to send it. Different beam patterns, or states, are also possible—for example, you might want a broader beam if you are sending the same signal to multiple receivers in a given direction, or a tighter beam if you are talking to just one.

Now, researchers have developed an advanced liquid-based antenna system that relies on a readily available ingredient: saltwater.

To be sure, this is not the first liquid antenna: these antennas, which use fluid to transmit and receive radio signals, can be useful in situations where VHF or UHF frequencies are required (frequencies between 30 megahertz and 3 gigahertz). They tend to be small, transparent, and more reconfigurable than conventional metal antennas. For these reasons, they are being explored in for some internet of things (IoT) and 5G applications.

Liquid antennas that depend on salty water have even more benefits, since the substance is readily available, low-cost and eco-friendly. Several saltwater-based antennas have been developed to date, but these designs are limited in how easily the beam can be steered and reconfigured.

However, in a recent publication in IEEE Antennas and Wireless Propagation Letters, Lei Xing and her colleagues at the College of Electronic and Information Engineering at Nanjing University of Aeronautics and Astronautics in China have proposed a new saltwater-based antenna that achieves 12 directional beam-steering states and one omnidirectional state. Its circular configuration allows for complete 360-degree beam-steering and works for frequencies between 334 to 488 MHz. [READ MORE]