François Torres

Application of fractional derivatives to the FDTD modeling of pulse propagation in a Cole–Cole dispersive medium

This article presents an application of the fractional derivative concept to the modeling of the time-domain propagation in dispersive Cole-Cole media. A recursive finite-difference(SINGLEBOND)time-time-domain (FDTD) formulation is developed to solve the special differential equation that is obtained. This formulation is validated by comparing the calculated permittivities to analytical values.

Synthesis of Antenna Arrays and Parasitic Antenna Arrays with Mutual Couplings

A synthesis method to design multielement antennas with couplings is presented. The main objective is to perform a rigorous determination of the electromagnetic characteristics involved in the design, especially with arrays of moderate sizes. The aim is to conceive jointly and efficiently the antenna and the circuits to connect (feed distribution network, power amplifiers, reactive loads, etc.). The subsequent objective is to improve the understanding and capabilities of strongly coupled antennas. As a whole, the synthesis procedure is then applied to different antenna architectures in order to show its efficiency and versatility. A focus on some antenna concepts where the management of couplings is a key factor to improve the performances is presented. After describing the synthesis procedure, the first category of coupled multielement antenna studied concerns radiating arrays in linear or circular polarization. A design including couplings effects on an active array is also presented. Then, the method is applied to parasitic antenna arrays and a specific investigation on reflectarray antenna is performed as they can be considered as a particular case of parasitic arrays.

EM/Circuit Mixed Simulation Technique for an Active Antenna

Todays increase of functions, improvement of performance, and cost reductions required on an active electronically scanned array (AESA), associated to the limited amount of available areas and volumes to implement the equipment, drive an approach leading to directly connect power amplifiers (PAs) to the antennas array without placing an isolator/circulator between them. In this letter, an electromagnetic/radio frequency (EM/RF) circuit mixed simulation technique will be theoretically introduced and experimentally demonstrated on transmission (Tx) chains to deal with the proposed challenge.

An accurate modeling technique for antennas and nonlinear RF power amplifier mixed simulation

The design of agile active antennas requires an efficient modeling methodology in order to quantify the impact of other components on the array radiation pattern, and especially the influence of power amplifiers (PA). Therefore, the performance prediction of PA on TX chains is of prime importance. This article describes two different approaches for active antenna applications. The first one concentrates on PA macro-modeling, which takes into account a large output load impedance mismatch with a voltage standing wave ratio up to 4:1. A PA behavioral model based on nonlinear scattering functions was developed and extracted from CW measurements. The model validity was checked by comparison with the measured data. The second one describes a novel technique for synthesizing a given radiation pattern, whereas taking into account the mutual coupling and calculated matching impedances (ZL =50 V) of each antenna in the array according to frequency and pointing angle.

Mixed simulation approach for direct connection between power amplifiers and antenna arrays without the use of isolators

This paper describes a mixed simulation approach of electromagnetic (EM) macromodel and nonlinear circuit bilateral model to correct the output signal for a power amplifier (PA) and obtain an optimal radiation pattern for an active antenna array transmit (TX) chain. Various experimental results show the reliability of EM, nonlinear PA models and mixed simulation approach as well. The originality of this work is the elimination of isolators between PAs and antennas while maintaining a matched PA and a correct radiation pattern in regards to the antennas high impedance mismatch.

Power amplifiers modeling technique for reconfigurable antenna array application

The design of reconfigurable active antennas requires an efficient system simulation in order to analyze the impact of other components on the array pattern, especially the Power Amplifiers (PA) effect. Therefore, the performance prediction of PA on Tx-Rx chains is important. This paper presents a behavioral model of a PA, which is able to take into account the load impedance mismatch with a VSWR (Voltage Standing Wave Ratio) up to 3. The proposed behavioral model, based on non-linear scattering functions, is extracted from simple CW measurements, and then implemented in Agilent Advanced Design System (ADS). Our behavioral model is validated by comparison with measurement results in the case of loading impedance mismatch (VSWR ≤ 3). Another model was validated (expansion of Taylor series to the second order), taking into account large VSWR (VSWR =3.5).

Co-design and co-integration of multiband active antenna arrays for satellite radionavigation systems

This paper presents the structuration and the first results of a research program dedicated to the co-design and the co-integration of a multiband antenna array for a GPS/Galileo receiver. The objective is to develop a novel design approach taking into account all parts of the RF system simultaneously. By this way, the aim is to improve the performances of the RF front-end compared to a traditional approach where RF circuits would be designed separately.

Modeling and Analysis of Large-Signal RFI Effects in MOS Transistors

The ability of radio-frequency (RF) interference signals to upset or disrupt electronic equipment is a matter of concern, and identification of the physical mechanisms leading to device malfunction is of prime importance. This paper presents experimental and theoretical results and analyzes the effects of a large-signal microwave excitation up to 2 GHz on several commercial small-signal MOS transistors. For frequencies beyond the maximum operating frequency, experimental results show RF signal rectification in the devices, and these results are confirmed by SPICE simulations using extracted models for the transistors, including package and test circuit parasitics, with excellent agreement with experiments. Analysis of internal transistors currents and voltages finally leads to the conclusion that the observed rectification effect is not due to active nonlinearities of the devices, but rather due to the nonlinear overlap and parasitic drain–bulk diode capacitances of the MOS transistors. In particular, the role of the nonlinear voltage dependence of the junction capacitance is highlighted. Finally, a simplified model is proposed to reproduce this behavior.

Synthesis method for matching filters

The aim of this paper is to develop an exact synthesis technique for matching filters in connection with the use of single band antennas. A certified algorithm based on Youlas matching theory and convex optimization is presented. A practical example is considered with the synthesis of a matching filter in SIW technology used behind a microstrip patch antenna at 1.5 Ghz.

Control of a Mos Inverter by Out-of-Band Pulsed Microwave Excitation

An intentional focusing of High-Power Microwave (HPM) energy on microelectronic systems can produce effects that will potentially upset or damage the target. However, the physical mechanisms at work within the device are not often well understood. We provide a detailed understanding of the physical mechanisms involved in a common-source Metal Oxide Semiconductor (MOS) transistor inverter when Pulsed Microwave Excitation (PME) in a frequency range from 10 MHz to 1 GHz is applied on the gate terminal. Our study is based on the measurements of the current waveforms on all transistor access and explains the MOS response with and without the Radio-Frequency (RF) interference.