A digital upconversion system for an N-th order multi-band multi-order power amplifier, MOPA, configured to amplify a multi-band signal (S MB-1,..,S MB-N) comprising N inputs (22-1,...,22-N) comprising a different input (22-1,...,22-N) per each of the order N, where N is greater than or equal to 2, and wherein the multi-band signal comprises M narrowband signals (S BB,1,...,S BB,M) in M frequency bands of the multi-band signal wherein, M is greater than or equal to 2, comprising: - per each frequency band of the M frequency bands of the multi-band signal: a digital signal splitter (26-1,...,26-M) configured to split a digital baseband signal (S BB,1,...,S BB,M) for the frequency band into N baseband split signals (S BB,1-1,...,S BB,1-N,...,S BB,M-1,...S BB,M-N) for the frequency band, each of the N baseband split signals for the frequency band being for a different order of the order N of the multi-band MOPA; and -- per each baseband split signal (S BB,1-1,...,S BB,1-N) for the frequency band of the N baseband split signals for the frequency band: a digital upconverter configured to digitally upconvert the baseband split signal for the respective frequency band to a desired upconversion frequency to thereby provide an upconverted split signal (S UP,1-1,...,S UP,1-N) for the frequency band, the digital upconverter comprising one or more calibration actuators (34, 28,...,28(1-N)) configured to independently control a gain (G 1-1,...,G 1-N), a phase (Φ 1-1,...,Φ 1-N), and a delay (T 1-1,...,T 1-N) of the upconverted split signal for the frequency band; and circuitry (30, 32) configured to process the upconverted split signals for the M frequency bands of the multi-band signal for each of the order N of the multi-band MOPA to provide a plurality of multi-band split signals (S MB-1,...,S MB-N) for the plurality of inputs of the multi-band MOPA, wherein the circuitry (30, 32) further comprises, for each order of the order N of the multi-band MOPA: - a digital combiner (30-1...,30-N) configured to digitally combine the upconverted split signals for the M frequency bands of the multi-band signal for the order of the multi-band MOPA to provide a combined upconverted digital signal (S COMB-1,...,S COMB-N) for the respective order of the multi-band MOPA. - per each frequency band of the M frequency bands of the multi-band signal: a digital signal splitter (26-1,...,26-M) configured to split a digital baseband signal (S BB,1,...,S BB,M) for the frequency band into N baseband split signals (S BB,1-1,...,S BB,1-N,...,S BB,M-1,...S BB,M-N) for the frequency band, each of the N baseband split signals for the frequency band being for a different order of the order N of the multi-band MOPA; and -- per each baseband split signal (S BB,1-1,...,S BB,1-N) for the frequency band of the N baseband split signals for the frequency band: a digital upconverter configured to digitally upconvert the baseband split signal for the respective frequency band to a desired upconversion frequency to thereby provide an upconverted split signal (S UP,1-1,...,S UP,1-N) for the frequency band, the digital upconverter comprising one or more calibration actuators (34, 28,...,28(1-N)) configured to independently control a gain (G 1-1,...,G 1-N), a phase (Φ 1-1,...,Φ 1-N), and a delay (T 1-1,...,T 1-N) of the upconverted split signal for the frequency band; and -- per each baseband split signal (S BB,1-1,...,S BB,1-N) for the frequency band of the N baseband split signals for the frequency band: a digital upconverter configured to digitally upconvert the baseband split signal for the respective frequency band to a desired upconversion frequency to thereby provide an upconverted split signal (S UP,1-1,...,S UP,1-N) for the frequency band, the digital upconverter comprising one or more calibration actuators (34, 28,...,28(1-N)) configured to independently control a gain (G 1-1,...,G 1-N), a phase (Φ 1-1,...,Φ 1-N), and a delay (T 1-1,...,T 1-N) of the upconverted split signal for the frequency band; and - a digital combiner (30-1...,30-N) configured to digitally combine the upconverted split signals for the M frequency bands of the multi-band signal for the order of the multi-band MOPA to provide a combined upconverted digital signal (S COMB-1,...,S COMB-N) for the respective order of the multi-band MOPA.