Minimizing radiated power variation in power amplifier FEMs with directional couplers

Directional couplers are used in GSM/EDGE and 3G power amplifier front end modules (PA FEMs) for radiated power detection and control. The radiated power varies with load VSWR. There are analyses on the power control mechanism in PA FEMs with directional couplers, and back-of-envelope calculations to estimate power variations in design practice. The objective of the paper is to provide engineering examples illustrating the pros and cons of various methods, and design considerations to compensate non-ideal factors in PA FEMs.