There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The authors show that the Taylor-series coefficients of a FET's gate/drain I/V characteristic, which is used to model this nonlinearity for Volterra-series analysis, can be derived from low-frequency RF measurements of harmonic output levels. The method circumvents many of the problems encountered in using DC measurements to characterize this nonlinearity. This method was used to determine the incremental gate I/V characteristic of a packaged Aventek AT10650-5 MESFET biased at a drain voltage of 3 V and drain current of 20 mA. The FET's transconductance was measured at DC, and its small-signal equivalent circuit (including the package parasitics) was determined by adjusting its circuit element values until good agreement between calculated and measured S parameters was obtained. The FET was then installed in a low-frequency test fixture. Excellent results were obtained. >

Modeling the gate I/V characteristic of a GaAs MESFET for Volterra-series analysis

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Microstrip And Printed Antenna Design

A comparative study among several nonlinear high-power amplifier (HPA) models using real measurements is carried out. The analysis is focused on specific models for wideband OFDM signals, which are known to be very sensitive to nonlinear distortion. Moreover, unlike conventional techniques, which typically use a single-tone test signal and power measurements, in this study the models are fitted using subsampled time-domain data. The in-band and out-of-band (spectral regrowth) performances of the following models are evaluated and compared: Saleh's model, envelope polynomial model (EPM), Volterra model, the multilayer perceptron (MLP) model, and the smoothed piecewise-linear (SPWL) model. The study shows that the SPWL model provides the best in-band characterization of the HPA. On the other hand, the Volterra model provides a good trade-off between model complexity (number of parameters) and performance.

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Modeling nonlinear power amplifiers in OFDM systems from subsampled data: a comparative study using real measurements

In this paper, we present a comparative study of three neural networks-based solutions for large- and small-signal modeling of MESFET and HEMT transistors. The first two neural architectures are specific for this modeling problem: the generalized radial basis function (GRBF) network, and the smoothed piecewise linear (SPWL) model. These models are compared with the well-known multilayer perceptron (MLP) network. Results are presented for both the large- and small-signal regimes separately. Finally, a global model is proposed that is able to accurately characterize the whole behavior of the transistors. This model is based on a simple combination of the best models obtained for the two kinds of regimes.

Neural networks for large- and small-signal modeling of MESFET/HEMT transistors

In this paper we present the smoothed piecewise-linear (SPWL) model as a useful tool in the device modeling field. The SPWL model is an extension of the well-known canonical piecewise-linear model proposed by Chua, which substitutes the abrupt absolute value function for a smoothing function (the logarithm of hyperbolic cosine), thus providing the model with several interesting properties. In particular, this function makes the model derivable, which is important to predict the intermodulation distortion behavior. Moreover, it allows one to control the smoothness of the global model by means of a single smoothing parameter. The parameters of the model are adapted to fit the nonlinear function, while the smoothing parameter is selected according to derivative constraints. The applied learning algorithm is a second-order gradient method. The proposed SPWL model is successfully applied to model a microwave HEMT transistor under optical illumination using real measurements. The model receives as input the bias voltages of the transistor, the instantaneous voltages, and the optical power and provides the drain to source current. The performance and computational burden of the SPWL model is compared with an empirical model and with some neural networks-based alternatives.

Smoothing the canonical piecewise-linear model: an efficient and derivable large-signal model for MESFET/HEMT transistors

The aim of this work is to miniaturize a microstrip patch antenna array resonating at 10 GHz. It presents an improved method of size reduction of a microstrip antenna array with circular polarisation using Defected Ground Structure (DGS) which is used to perform serious LC resonance property in certain frequency. By integrating Defected Ground Structure elements, the resonance frequency was shifted from 10 GHz to 7.5 GHz. The proposed structure of DGS is incorporated in the ground plane of our array antenna. Prototype of the antenna was fabricated with FR4 substrate and tested. The simulation and measurement results were in good agreement.

A miniature microstrip patch antenna array with defected ground structure

In this paper, switched beam smart antenna systems are investigated to improve the performance of wireless networks. The microstrip technology of antenna arrays with Butler matrix topology as a beam-former is used to implement the switched beam smart antenna system. The optimum design of a 4x4 planar Butler matrix array, operating at 5.6 GHz for WLAN applications. System’s design and optimization was based on computer simulations.

Design and implementation of a technology planar 4x4 butler matrix for networks application

This paper explores optimization and synthesis of linear, which prints antennas arrays. The developed synthesis bases on an optimization binomial method. The objective of this paper is to adapt the binomial method to reduce the side lobe level. The application of this formalism gives terrific results.

Reducing side lobes of antenna array by the binomial method

Schottky diodes fabricated by the University of Virginia in USA have been subject of intense recent investigation and have emerged as attractive candidates at THz frequencies. Single Schottky diodes have junctions with extremely low junction capacitance, and low series resistance which makes them extremely well-suited for commutating mixer circuits in which ideal switching behaviour is highly desirable [1]. Schottky diodes also offer lower forward voltage compared to an otherwise equivalent p-n junction diode. This permits Schottky diodes to detect lower amplitude signals than a p-n junction. In this paper we describe a procedure to extract the parameters of a high performance THz Schottky diode. Model extraction is done using a combination of dc and small-signal RF measurements. The results show that the proposed method is suitable to determine parameters of diode model with the excellent fit between measured and calculated I-V DC and Sparameter. I. INTRODUCCION Los diodos Schottky se han utilizado durante varias decadas como elementos clave en la mezcla de frecuencias y la deteccion de potencia en radiofrecuencia. En 1938 Walter Schottky, hijo del matematico aleman Friedrich Shottky [2], explico la manera en la que un compuesto formado por metal y un semiconductor dopado puede rectificar. El diodo Schottky es el resultado de este trabajo. Los diodos Schottky fabricados en Arseniuro de Galio (GaAs) tienen una barrera de potencial baja, lo que se traduce en una alta sensibilidad, caracteristica muy importante para dispositivos que tienen que detectar senales muy debiles. El modelo fisico de un diodo esta basado en las caracteristicas fisicas del dispositivo, lo que permite reproducir el comportamiento del mismo para cualquier tipo de senal de entrada. El modelo circuital de diodo esta basado en la topologia clasica que tiene en cuenta los mecanismos fisicos observables en un diodo Schottky, como son la emision termoionica [3], mecanismo que explica la corriente que fluye a traves de la union. Este articulo plantea un procedimiento de obtencion del modelo circuital equivalente lineal y no lineal de un diodo Schottky, por ser el elemento clave de los detectores mezcladores, multiplicadores, etc. de altas frecuencias. La extraccion del modelo se basa en dos tipos de medidas. Se realizara el modelado en continua del diodo, tambien se obtendra el comportamiento en AC del diodo, mediante el modelado de los parametros de Scattering hasta 45 GHz. II. MODELADO DEL DIODO SCHOTTKY EN CONTINUA (DC) En este trabajo se mostrara la caracterizacion del diodo Schottky modelo W Bande Single Anode de la Universidad de Virginia. En la figura 1 se muestra una foto del diodo, [4]. Fig. 1. Foto Del Diodo Schottky Single El modelo total se conseguira mediante la combinacion de medidas en continua y alterna, que nos permiten obtener la caracterizacion corriente-tension (I/V) especifica del diodo y los parametros [S]. El modelo de equivalente gran senal del diodo es el representado en la figura 2 [5]: Fig. 2. Modelo Equivalente Gran Senal del Diodo Lp

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Antonio Tazón Puente

Papers

Smoothing the canonical piecewise-linear model: an efficient and derivable large-signal model for MESFET/HEMT transistors

A miniature microstrip patch antenna array with defected ground structure

Design and implementation of a technology planar 4x4 butler matrix for networks application

Reducing side lobes of antenna array by the binomial method

Modelado de diodos Schottky para aplicaciones a frecuencias de terahercios