Plasma antenna technology for new communication systems

An inspired design for the emerging technology of plasma antennas ticks all the performance boxes: power efficiency, reconfigurability, small size, portability, and extended lifetime.

A plasma antenna is a type of radio antenna currently in development in which plasma replaces the metal elements of a traditional antenna. A type of plasma antenna – gas plasma antenna – uses a discharge tube instead of metal elements. As the current flows through the tube, the gas gets partially or fully ionized to plasma, becomes conductive, and acts as a mirror, eventually transmitting and receiving signals. Above the plasma frequency, plasma antennas are virtually transparent to a great bandwidth of electromagnetic waves and become invisible when the system is powered off and gas de-ionizes. Unlike conventional antenna designs, plasma designs can be reconfigured electrically (rather than mechanically) with respect to impedance, frequency, bandwidth, and directivity on time scales extending from the microsecond to the millisecond. It is also possible to stack arrays of gas plasma antennas to operate at different frequencies. Plasma has a very high electrical conductivity, which aids in the receipt, direction and transmission of various types of radio signals. The technology boasts many unique advantages, but there is always room for improvement in performance, and this is what researchers under the EU-funded PATH project achieved. “Improvement of plasma source performances require strong efforts in term of modelling and technology. Overcoming the density limit of current plasma source will open up a variety of new applications in several technological fields,” notes Alessio Di Iorio, project coordinator, and CEO at Alma Sistemi.

Testing a hybrid source concept

Researchers first developed two types of plasma sources: a compact, radiofrequency one and a hollow-cathode one allowing for high plasma densities and longer-life antennas. Detailed physical models of both plasma sources describe the interactions between plasma and electromagnetic radiation. “Until now, several research efforts focused on optimizing plasma sources in terms of either power efficiency, reconfigurability, size, density or lifetime. Despite their success, it has not been possible to achieve progress on all fronts,” explains Di Iorio. In fact, further research is required especially in the area of materials to reach an adequate technology readiness level. PATH laid the foundations for a new class of technology that combines the best properties of radiofrequency and hollow-cathode plasma sources. The hybrid source design enabled further increases in plasma density (exceeding 10^20 ion per cubic metres), which added to the antenna performance. Merging expertise from different fields, PATH explored how this hybrid technology concept could be used in telecommunications and navigation applications.

Unique characteristics of plasma antenna technology

“The experimental results of the newly developed prototypes demonstrated that active plasma antennas behave much like the metallic ones. The most notable difference when comparing these two antenna types lies in the gain, which is lower for the plasma antennas,” notes Di Iorio. “On the other hand, when the antenna elements are inactive, they do not interfere with the active electric fields of nearby antenna elements. In other words, when switched off, they become transparent to the electromagnetic waves radiated by other elements.” The overall gain of plasma antenna arrays also proved to be invariant to the choice of the active antenna element – as long as the geometry of active elements remained the same. By contrast, each antenna element in metallic antenna arrays affected channel gain in a different way.

Market applications of plasma antenna technology

“Ensuring reliable antenna performance at high frequencies and fast tunability/high reconfigurability is of paramount importance to the future information society,” says Di Iorio. The advantages of plasma antennas over conventional metal ones are most obvious in military applications, where stealth and electronic warfare are primary concerns. “We also expect that the technology will be a promising candidate in smartphones and other consumer electronics, wearable wireless communications, and biomedical radiofrequency systems,” concludes Di Iorio.

Keywords

PATH, plasma, plasma antenna, reconfigurability, plasma source, density, gain, radiofrequency, hollow cathode, metallic antenna

Arsalan Fazal