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High Power Amplifier (high + power_amplifier)
Selected AbstractsAdaptive predistortion of COFDM signals for a mobile satellite channelINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2003Nibaldo Rodriguez Abstract In this paper, we consider the optimization of the performance of QPSK and 16-QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non-linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non-linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non-linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10,3 when compared to QPSK COFDM without the predistortion scheme and 16-QAM COFDM provides a gain of 0.5 dB output back-off and 1.2 dB signal to noise ratio at a BER of 3×10,5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10,4 for QPSK and 16-QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd. [source] A fully matched 9 W compact PHEMT MMIC high power amplifier for X-band phase array radar applicationsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2007Chen-Kuo Chu Abstract This paper presents a compact X-band, 9 W AlGaAs/InGaAs/GaAs PHEMT MMIC high power amplifier. This amplifier is designed to fully match a 50 , input and output impedance. Based on 0.35 ,m gate-length power PHEMT technology, a two-stage power amplifier is fabricated on a 3-mil thick wafer. While operating under 9 V DC bias condition, the characteristics of 17 dB small-signal gain, an average of 9 W continuous-wave output power, and 34% power added efficiency from 9.0 to 10.5 GHz can be achieved. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 257,261, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22102 [source] Natural gradient algorithm for neural networks applied to non-linear high power amplifiers,INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2002H. Abdulkader Abstract This paper investigates the processing techniques for non-linear high power amplifiers (HPA) using neural networks (NNs). Several applications are presented: Identification and Predistortion of the HPA. Various Neural Network structures are proposed to identify and predistort the HPA. Since a few decades, NNs have shown excellent performance in solving complex problems (like classification, recognition, etc.) but usually they suffer from slow convergence speed. Here, we propose to use the natural gradient instead of the classical ordinary gradient in order to enhance the convergence properties. Results are presented concerning identification and predistortion using classical and natural gradient. Practical implementations issues are given at the end of the paper. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||