Overview

From APPLIED MICROWAVE & WIRELESS, VOL.12, NO.7, JULY 2000

Multicarrier personal communications systems often require power amplifiers with approximately constant 1 dB gain compression point and saturated output power across the frequency range of use. For portable or satellite applications it is also desirable to have high gain, high efficiency and a uniform temperature coefficient over the frequency range. A design procedure for a two-stage GaAs FET amplifier based on control of the load line over frequency and proper selection of FET size ratio between the stages has been developed to achieve the desired characteristics. The resulting circuits are compact and do not require feedback. The method has resulted in consistently successful design of both hybrid MIC and monolithic MMIC amplifiers at L-band (1.414 GHz) and S-band (2.12 GHz) for both geosynchronous earth orbit (GEO) and medium earth orbit (MEO) satellite to mobile telephone applications. Over a 10 percent operating bandwidth in this frequency range, typical 3-watt, single-ended designs provide 26 dB small-signal gain, 60 percent power added efficiency (PAE) in saturation and 0.5 dB flatness in saturated output power level.

Design Procedure

The following procedure illustrates the design of a 3-watt amplifier, but the technique can also be used to design amplifiers at higher or lower power levels. The design begins with the second stage output matching network and proceeds toward the first stage input network.

The load line resistance for the second stage is determined from...