We have investigated several configurations of antennas based on graphene. We show that patterned metallic dipole antennas or arrays of dipole antennas deposited on graphene highly benefit from the reversible high-resistivity-to-low-resistivity transition in graphene, tuned by a gate voltage. The radiation pattern and the efficiency of such antennas are changed via the gate voltage applied on graphene.

In this letter, we demonstrate that a graphene monolayer, over which three metallic electrodes forming a coplanar waveguide are patterned, acts as a frequency multiplier and generates frequencies at least up to 40 GHz. These results show that monolayer graphene is a natural frequency multiplier.

We present the modeling and measurements of microwave propagation in a coplanar waveguide over graphene in the range of frequencies 40 MHz-110 GHz, which suggest that graphene could work well in a very large bandwidth. Graphene is acting as a natural matching device because its equivalent resistance at these frequencies is able to vary more than 75% when DC biases are applied in the range −4 V to 4 V on the graphene waveguide.

We investigated a double-clamped graphene device positioned over a planar waveguide in which propagate electromagnetic fields up to 60 GHz. Several double-clamped graphene flakes display good characteristics in enabling and disabling the propagation of high-frequency electromagnetic fields. The same characteristics were retrieved in a graphene switch based on the rapid change in the resistivity due to an applied gate voltage. Both devices are among the fastest switches, the switching time being very short less than 1 ns.

This paper proposes and validates a new principle in coplanar waveguide (CPW) bandstop filter tuning by shortcutting defected ground plane (DGS) inductor shaped spirals to modify the resonant frequency. The tunable filter is fabricated on a high-resistivity silicon substrate based on a CMOS compatible technology using a 1 μm x 10 μm long and 300 nm thick vanadium oxide (VO ₂ ) switch by exploiting its insulator to metal transition. The filter is designed to work in Ka band with tunable central frequencies ranging from 28.2 GHz to 35 GHz. The measured results show a tuning range of more than 19 %, a low insertion loss in the neighboring frequency bands (below 2 dB at 20 GHz and 40 GHz in on/off-states) while a maximum rejection level close to 18 dB in off-state, limited by the no RF-ideal CMOS compatible substrate. The filter has a footprint of only 0.084 · λ ₀ x 0.037 · λ ₀ (where λ ₀ represents the free space wavelength at the highest resonance frequency) thus making it the most compact configuration using CPW DGS structures for the Ka frequency band. In addition, a more compact filter concept based on the Peano space filling curve is introduced to increase the tuning range while minimizing the DGS area.

This letter proposes a spherical 3-D Smith Chart suitable for representing both active and passive microwave circuits. Using the mathematical concept of the Riemann sphere, the extended reflection coefficient plane is transformed into the surface of the unit sphere. Since the proposed Smith Chart compiles the whole complex plane, all possible loads are included. A simple graphic tool is thus obtained that successfully unifies active and passive circuits. In addition, lossy lines with complex characteristic impedances can also be represented. The letter presents the 3-D Smith Chart, provides its main governing equations, and also enumerates its more important properties.