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A 40Watt linear power amplifier based on silicon LDMOSFETs is presented. It has ultra broadband characteristics from 2 to 512 MHz. The proposed amplifier has a push-pull structure using Guanella 1:1 and 1:4 transmission line transformers for its input and output baluns, respectively. A negative feedback network is also adopted for broadband operation with a flat gain response. To achieve high linearity, the bias condition for almost class-A operation is applied. Based on the proposed concept, a two-stage broadband amplifier is implemented. A P1dB of more than 40 Watt (46dBm) is achieved over the entire frequency band. The implemented power amplifier exhibits a power gain response of 43.3±1.8dB and a PAE of greater than 28.3% at each P1dB over the band. The second- and third-harmonic distortions are below -28.5dBc and -19dBc at each P1dB, respectively. Furthermore, at an average output power level of 41dBm for the two-tone signal input, which has a tone spacing of 1 MHz, the IMD3 over the entire band is below -30.1dBc.