A. Costantini

A computer simulation study of the formation of liquid crystal nanodroplets from a homogeneous solution.

The aggregation of liquid crystal nanodroplets from a homogeneous solution is an important but not well understood step in the preparation of various advanced photonic materials. Here, the authors performed molecular dynamics computer simulations of the formation of liquid crystalline nanodroplets, starting from an isotropic and uniform binary solution of spherical Lennard-Jones (solvent) and elongated ellipsoidal Gay-Berne (solute) rigid particles in low (<10%) concentration. They studied the dynamics of demixing and the mesogen ordering process and characterized the resulting nanodroplets assessing the effect of temperature, composition, and specific solute-solvent interaction on the morphology, structure, and anisotropy. They find that the specific solute-solvent interaction, composition, and temperature can be adjusted to tune the nanodroplet growth and size.

Accurate prediction of PHEMT intermodulation distortion using the nonlinear discrete convolution model

A general-purpose, technology-independent behavioral model is adopted for the intermodulation performance prediction of PHEMT devices. The model can be easily identified since its nonlinear functions are directly related to conventional DC and small-signal differential parameter measurements. Experimental results which confirm the model accuracy at high operating frequencies are provided in the paper.

A simplified approach for quasi-linear power amplifier distortion evaluation

The paper presents a simplified approach for the evaluation of mild distortion in highly linear power amplifiers (PA) for microwave communications. In particular, it is shown how intermodulation distortion (IMD) can be accurately predicted on the basis of a single-tone power-swept Harmonic Balance analysis instead of using two-tone or multi-tone analyses leading to time-consuming and computationally expensive iterative PA design procedures. Moreover, simple equations provided in the paper show that common design specifications given in terms of maximum acceptable IMD are conveniently converted into constraints on a suitable non linearity index, involving both AM/AM and AM/PM amplifier characteristics. Experimental validation is provided in the paper on the basis of a 50¿-loaded GaAs 600¿m-PHEMT based power amplifier simulated with Agilent ADS.

Power amplifier ACPR simulation using standard harmonic balance tools

The adoption of complex digital modulation techniques in wireless communication systems has posed a great demand on RF and microwave power amplifier performance. When high linearity is required, the amplifier characterization is based on intermodulation or, more commonly, on Adjacent Channel Power Ratio (ACPR) and other parameters more directly related to the actual circuit operation. In this paper a previously proposed Harmonic Balance (HB) algorithm is adopted for the ACPR simulation of power amplifiers excited by digitally modulated signals. With respect to other approaches the proposed technique provides fast and accurate results using a conventional HB engine without requiring special purpose algorithms.