A Low Distortion and High Efficiency Paralleled Power Amplifier without an Isolator in Wide Range of Load Impedances

Hikaru IKEDA
Hiroaki KOSUGI
Tomoki UWANO

IEICE TRANSACTIONS on Electronics   Vol.E80-C    No.6    pp.763-767
Publication Date: 1997/06/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Microwave and Millimeterwave High-power Devices)
microwave amplifier,  low distortion,  high efficiency,  paralleled amplifier,  π/4-DQPSK,  

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Characteristics of a distortion, gain and efficiency of a power amplifier grow worse extremely by different phases of the load reflection coefficient when load impedances of the power amplifier are far from 50 Ω. It was found that the value of the distortion, gain and efficiency showed the tradeoff behavior when the phase of the reflection coefficient was different in 180 degrees. Therefore we have proposed new two- and four-parallel unit power amplifiers combined in 90 degree and 45 degree different phases each in order to accomplish low distortion and high efficiency in wide range of load impedances without an isolator. We studied the power amplifiers by simulation based on experiments and realized an amplifier in that adjacent channel leakage power of π/4-DQPSK modulation (for Japan's digital cellular system) is less than -45 dBc and efficiency is over 45% in range of load VSWR less than 3.