Graphene-Based Phase Shifters Pave The Way for Terahertz Inter/Intra-Chip Communication

In the near future, vector modulators, beamforming networks, phased-array antennas, and phase discriminators made from integrally gated graphene-based waveguides may allow for the realization of sub mm-wave electronic switches and tunable loaded lines. At the University of Texas at Austin, terahertz (THz) antenna phase shifters made from integrally gated graphene parallel-plate waveguide (GPPWG) transmission lines have been proposed by Pai-Yen Chen, Christos Argyropoulos, and Andrea Alu. With theoretical and numerical demonstrations, several analog and digital phase shifters for THz frequencies based on GPPWG were shown to exhibit low loss, compact size, low phase error, and wide phase shift ranges for enhanced phase tuning capabilities.

The results demonstrated by the proposed analog, digital, and loaded line phase shifters could be attributable to the strong surface plasmon polariton wave localization of the graphene-based waveguides used in the designs. Other potential advantages include the capability to tune the propagation constant and the characteristic impedance of the waveguides by controlling the doping of the graphene components. 

To solve the possible matching issues with loaded-line phase shifters, multistage GPPWG tunable matching networks could be placed between the loaded lines. These matching networks would be tuned by biasing the graphene layers to achieve the desired phase shifts. Analog phase shifters in the THz frequency range could be realized by creating variable inductors from GPPWG by adding a graphene monolayer.

Practical high-speed digital phase shifters require stable high-speed switches. A GPPWG switch could be the solution when integrated with a double gate, enabling the use of the gate voltage for controlling the switch electrically with an effectively biased gate section. See “Terahertz Antenna Phase Shifters Using Integrally-Gated Graphene Transmission-Lines,” IEEE Transactions On Antennas And Propagation, April 2013, p. 1528.