Exploiting ambipolar electrical conductivity based on graphene field‐effect transistors has raised enormous interest for high‐frequency (HF) analog electronics. Controlling the device polarity, by biasing the graphene transistor around the vertex of the V‐shaped transfer curve, enables to redesign and highly simplify conventional analog circuits, and simultaneously to seek for multifunctionalities, especially in the HF domain. This study presents new insights for the design of different HF applications such as power amplifiers, mixers, frequency multipliers, phase shifters, and modulators that specifically leverage the inherent ambipolarity of graphene‐based transistors.

A small-signal equivalent circuit for graphene field-effect transistors (GFETs) is proposed considering the explicit contribution of effects at the metal-graphene interfaces by means of contact resistances. A methodology to separate the contact resistances from intrinsic parameters, obtained by a deembedding process, and extrinsic parameters of the circuit is considered. The experimental high-frequency performance of three devices from two different GFET technologies is properly described by the proposed small-signal circuit. Some model parameters scale with the device footprint. The correct detachment of contact resistances from the internal transistor enables to assess their impact on the intrinsic cutoff frequency of the studied devices.

This work details the design of single- and double-stage maximum gain and low-noise high-frequency amplifiers at 2.4GHz using a compact carbon nanotube field-effect transistor model, which is initially calibrated with hysteresis-free experimental data from a technology suitable for high-frequency applications. Parameters of the compact model represent CNTFETs with maximum high-frequency gain and reduced highfrequency noise by eliminating the metallic tubes contribution. Studies on linearity of the amplifiers as well as the impact of the quality factor of the inductors used in the stabilization network and the density of the nanotubes on amplifier performance are presented. Results of RF amplifiers show that CNTFETs are credible contenders for developing applications in S-band because of their gain (around 12 dB for a double-stage gain design), low noise (NFmin = 1:5 dB for a single-stage LNA) and linearity performance (OIP3 around 15dBm for a single-stage gain amplifier design).

The use of carbon nanotube (CNT) field-effect transistors (FETs) in microwave circuit design requires an appropriate, immediate and efficient description of their performance. This work describes a technique to extract the parameters of an electrical equivalent circuit for CNTFETs. The equivalent circuit is used to model the dynamic and noise performance at low- and high-frequency of different CNTFET technologies, considering extrinsic and intrinsic device parameters as well as the contact resistance. The estimation of the contact resistance at the metal/CNTs interfaces is obtained from a Y-function based extraction method. The noise model includes four noise sources: thermal noise, thermal channel noise, shot channel noise and flicker noise. The proposed model is compared with a compact model calibrated to hysteresis-free experimental data from a high-frequency multi-tube (MT)-CNTFET technology. Additionally, it has been applied to experimental data from another fabricated MT-CNTFET technology. The comparison in both cases shows a good agreement between reference data (simulation and experimental) and results from the proposed model. Low- and high-frequency noise projections of the fabricated reference device are further studied. Noise results from both studied technologies show that shot noise mainly contributes to the total noise due to the presence of Schottky barriers at contacts and along the channel.

An experimentally-calibrated carbon nanotube compact transistor model has been used here to design two high-frequency (HF) circuits with two different functionalities each: a phase configurable amplifier (PCA) and a frequency configurable amplifier (FCA). The former design involves an in-phase amplifier and an inverting amplifier while the latter design embraces a frequency doubler as well as a distinct inverting amplifier. The specific functionality selection of each of the two HF circuit designs is enabled mainly by the inherent ambipolar feature at a device level. Furthermore, at a circuit level the matching networks are the same regardless the operation mode. In-phase and inverting amplification are enabled in the PCA by switching the gate-to-source voltage (V_GS) from -0.3 V to 0.9 V while the drain-to-source voltage (V_DS) remains at 3 V. By designing carefully the matching and stability networks, power gains of 4.5 dB and 6.7 dB at 2.4 GHz for the in-phase and inverting operation mode have been achieved, respectively. The FCA, in its frequency doubler operation mode, exhibits 20 dBc of fundamental-harmonic suppression at 2.4 GHz when an input signal at 1.2 GHz is considered. This frequency doubler functionality is enabled at V_GS=0.3 V, whereas at V_GS=0.9 V amplification of 4.5 dB is obtained while V_DS remains at 3 V in both cases. In both configurable circuits the stabilization and matching networks are the same regardless the bias-chosen operation mode. The circuits performance degradation due to metallic tubes in the device channel is studied as well as the impact of non-ideal inductors in each design. PCA and FCA operation modes are further exploited in high-frequency modulators.

This paper describes the design and characterization of an ultra-wideband (UWB) flexible antenna for personal mobile communications. This antenna was fabricated on a polyamide substrate and its surface is equal to 40 × 55mm ² . Modelling results were compared with measurements performed using a VNA for a frequency range from 1 to 20 GHz. A good agreement between model and measurements was found within the whole frequency range. Our design presented, respectively, measured/modelled return losses of lower than −10 dB in a frequency range between 2–20 GHz and 1.6–16.3 GHz. This feature ensures a proper operation for several mobile communication standards.