28GHz transceiver paves the way for future 5G devices

A 28GHz transceiver has been fabricated by scientists at the Tokyo Institute of Technology for stable, high-speed 5G communications.

The scientists say this transceiver is tiny, but very fast, reliable and accurate and trumps previous designs by taking a new approach for beam steering.

The new standard for mobile networks promises data rates and speeds at least an order of magnitude higher than those of 4G (LTE), while even allowing for smaller antennas and radio frequency (RF) transceivers because of the higher frequencies used.

Most transceivers designed for 5G employ RF phase shifters. Accurate phase shifting is important because it allows the transceiver to guide the main lobe of the radiation pattern of the antenna array. In other words, it is used to ‘point’ the antenna array towards a specific direction so that both communicating ends (transmitter and receiver) exchange signals with the highest power possible. However, using RF phase shifters brings about certain complications and does not quite make the cut for 5G.

To overcome this, the scientists, led by Associate Professor Kenichi Okada, developed this transceiver, employing a local oscillator (LO) phase shifting approach. Instead of using multiple RF phase shifters, they designed a circuit that they say allows the transceiver to shift the phase of a LO in steps of 0.04° with minimal error. In turn, this allows for a beam-steering resolution of 0.1°, which represents an improvement of an order of magnitude compared with previous designs. This means that antenna array can be made to precisely point towards the desired direction, the scientists explain.

According to the team, the proposed LO phase shifting approach solves another problem of using multiple RF phase shifters: calibration complexity. RF phase shifters require precise and complex calibration so that their gain remains invariant during phase tuning, which is a very important requirement for the correct operation of the device. The situation becomes worse as the array increases in size. On the other hand, the proposed phase shifting approach results in a gain variation that is very close to zero over the entire 360° range.

This new transceiver was implemented in a circuit board measuring 4mm × 3mm using minimal components. The team compared the performance of their device with that of other transceivers for 5G. According to the scientists, the data rate they achieved was approximately 10Gb/s higher than that achieved with other methods, while maintaining a phase error and gain variations an order of magnitude lower.

Bethan Grylls

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