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This brief presents an ultrabroadband (2- to 600-MHz band) linear power amplifier using a compact frequency-selective analog predistorter, which includes a capacitor having an optimized capacitance and a biased Schottky diode connected in series. It is shunted at the input of the main amplifier and has a frequency-selective third-order intermodulation generation capability using its optimized capacitance. A two-stage push-pull power amplifier, which has an ultrabroadband operation range from 2 to 600 MHz, was implemented and linearized using the proposed analog predistorter. It exhibited high 1-dB compression point (P1 dB) and power-added efficiency characteristics of over 43 dBm and 32% at each P1 dB for the entire operating band, respectively. At an average output power level of 36 dBm for the two-tone signal input, which has a tone spacing of 1 MHz, its third-order intermodulation distortion over the entire band is no higher than -39.1 dBc after linearization, as compared with -34.2 dBc before linearization.