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This paper proposes a wideband adaptive predistortion linearization system based on high-speed RF envelope modulation applied to the input signal of an RF power amplifier. An FPGA-based look-up table, fed by a digitized envelope power signal, controls the envelope modulation performed by an RF vector modulator. The advantages of this predistortion architecture over conventional baseband digital approaches are a wider bandwidth, and the elimination of the need for digital baseband I/Q streams. The predistortion system was implemented as a testbed. Using 3-carrier CDMA2000 and multi-tone signals, the linearization performances for a 0.5 W GaAs HFET and a 90 W peak envelope power (PEP) LDMOS power amplifier were examined on the testbed. In the third-order intermodulation distortion (IMD) region, the wideband multi-tone testing showed IMD suppressions of 9 to 13 dB over 63 MHz bandwidth and a range of 7 to 8 dB backoff. For the 90 W power amplifier, the system achieved adjacent channel power ratio (ACPR) improvement of 13 dB output power backoff.