Researchers double Wi-Fi broadband while halving chip size

The researchers at Columbia Engineering invented a new technology they call “full-duplex radio integrated circuits” which uses only one antenna to simultaneously transmit and receive at the same wireless radio frequency.

Key to full-duplex communications which virtually double the useful bandwidth in wireless communications is the circulator. This device transmits the signal entering a port to the next port in rotation. For instance, a three-port circulator where the three ports are “transmit” (1), “receive” (2) and “antenna” (3) works by routing (1) to (3), and (3) to (2). This way, you don’t get (1) to (2) which would’ve meant hearing yourself in a closed loop.

For more than 60 years, these sort of circulators have been used by the industry to provide two-way communications on the same frequency channel, but they are not widely adopted because of the large size, weight and cost associated with using magnets and magnetic materials. These magnets are essential to a working circulator because they “break” Lorentz Reciprocity — a physical constraint of most electronic structures that forces electromagnetic waves to travel in the same manner in forward and reverse directions.

Electrical Engineering Associate Professor Harish Krishnaswam and colleagues made a breakthrough by scrapping the magnets and using a mini-circulator that rotates the signal across a set of capacitors. They then devised a working prototype of a full-duplex system on a nanoscale silicon chip.

There’s a myriad of potential applications, from better radar, to faster WiFi, to isolator that prevent high-power transmitters from being damaged by back-reflections from the antenna. Anything that uses half-duplex functions, or virtually all cell phones and WiFi routers, could double performance.

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