25-GHz circulator eliminates magnets, paves the way for doubling data capacity and beyond

By Warren Miller, contributing writer

A new technique for creating millimeter-wave circulators on a single chip may make it possible to implement full-duplex or two-way wireless communications. Currently, wireless communications are limited to half-duplex or one-way operation. This breakthrough could not only double traffic in the crowded existing wireless frequencies but could also open up higher millimeter-wave frequencies at 30 GHz and above.

The new technique was recently published in Nature Communications by researchers at Columbia University in New York. They demonstrate an implementation of a 25-GHz circulator that fits on a single integrated circuit. This is made possible because the new technique eliminates the magnets that were needed in previous designs. Instead of magnets, the device uses a non-reciprocal structure, one with physical characteristics that differ depending on the direction of flow. As seen in the figure, the circuit has a pair of transmission lines at the top of the circuit (the straight section above the dual rings in the center). These lines are either directly connected or cross-connected, depending on the setting of the switches at the ends of the transmission lines. If the length is set precisely, and the switches at one end are 90° out of phase with the other, signals can travel in one direction but mutually cancel in the other.

Image source: engineering.columbia.edu.

According to the university, the method “enables loss-free, compact, and extremely broadband non-reciprocal behavior, theoretically from DC to daylight that can be used to build a wide range of non-reciprocal components such as isolators, gyrators, and circulators.” This technique can be used to create a three-port circulator, allowing the connection of both transmit and receive amplifiers at the same aerial. This type of connection could support full-duplex operation, “in which a transmitter and a receiver of a transceiver operate simultaneously on the same frequency channel, enables doubling of data capacity within existing bandwidth. Going to the higher mm-wave frequencies, 30GHz and above, opens up new bandwidth that is not currently in use.”

This approach could be an amazing boon to the wireless industry. Doubling data capacity could open up a wide range of new services, those that could reduce data charges for cell phone plans — wouldn’t that be welcome — or could offer increases in communications bandwidth, perhaps for cloud-based applications — maybe at a premium over current costs, however. Opening up new frequency ranges is exciting, too. Perhaps it would allow additional services and carriers and increase competition. This could bring down costs on a wide range of applications. Perhaps 4K class video and augmented reality will be less costly than what we have today. If a wide range of high-end frequencies become available, maybe the “Star Trek” Holodeck isn’t as far away as one might think, at least as far as the data communications requirements goes. It could be the artificial intelligence piece that might be a bit further out.