A 1 to 2 GHz, 50 Watt Push-Pull Power Amplifier Using SiC MESFETs

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  • Author: Raymond Pengelly and Carl Janke
Because of their high RF power densities and cor-respondingly low intrin-sic capacitances per watt of RF output power, sili-con carbide (SiC) MESFETs are becoming increasingly popular in very wideband ampli-fier applications. This article describes the design and realization of a single-stage linear power amplifier covering the 1,000 to 2,000 MHz frequency range. The amplifier uses a 3rd generation SiC MESFET produced by Cree Inc. in a brazed ceramic package having a copper-molybdenum-copper flange. The amplifier uses two transistors in a push-pull configuration together with commercially available Anaren Xinger® baluns. Thus, each half of the amplifier is matched at its input and output to 25 ohms—this makes matching the transistors over an octave bandwidth eas-ier and more efficient when compared to matching a single-ended amplifier of twice the power level to 50 ohms. Also the push-pull con-figuration affords higher harmonic and inter-modulation performances as well as superior thermal management, because the sources of heat from the two transistors are spread over a larger area when compared to a single device. The amplifier was designed using Cree’s proprietary large-signal MESFET model employing the Agilent ADS simulator.
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