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“Full-duplex communications, where the transmitter and the receiver operate at the same time and at the same frequency, has become a critical research area and now we have shown that WiFi capacity can be doubled on a nanoscale silicon chip with a single antenna. This has enormous implications for devices like smartphones and tablets,” he said

Krishnaswamy’s group has been working on silicon radio chips for full duplex communications for several years and became particularly interested in the role of the circulator, a component that enables full-duplex communications where the transmitter and the receiver share the same antenna.

In order to do this, the circulator has to “break” Lorentz Reciprocity, a fundamental physical characteristic of most electronic structures that requires electromagnetic waves travel in the same manner in forward and reverse directions.

“We wanted to create a simple and efficient way, using conventional materials, to break Lorentz Reciprocity and build a low-cost nanoscale circulator that would fit on a chip,” said PhD student Negar Reiskarimian, who developed the circulator.

The traditional way of breaking Lorentz Reciprocity and building radio-frequency circulators has been to use magnetic materials such as ferrites, which lose reciprocity when an  external magnetic field is applied.

But these materials are not compatible with silicon chip technology, and ferrite circulators are bulky and expensive. Krishnaswamy and his team were able to design a highly miniaturised circulator that uses switches to rotate the signal across a set of capacitors to emulate the non-reciprocal “twist” of the signal that is seen in ferrite materials.

Aside from the circulator, they also built a prototype of their full-duplex system – a silicon IC that included both their circulator and an echo-cancelling receiver.

The research was published in the journal Nature Communications.

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