A frequency-agile transmitter tunable to operate in each of a plurality of predetermined frequency bands, comprising: a baseband processing unit configured to receive a complex input signal and a feedback signal, and to output a pre-distorted baseband signal based on said complex input signal and said feedback signal; a programmable digital up-converter connected to the baseband processing unit, the programmable digital up-converter comprising: a complex baseband tuner; a digital up-sampler; a complex channel selection filter; and a quadrature modulator, wherein the programmable digital up-converter is configured to receive the pre-distorted baseband signal, and to convert the pre-distorted baseband signal into a digital signal having a spectral content which is selected based on at least one first control input received from the baseband processing unit, wherein the at least one first control input includes at least one of: filter information associated with a selected one of the predetermined frequency bands, complex tuner frequency and an up-sampling parameter associated with the selected one of the predetermined frequency bands; a digital to analog converter connected to the programmable digital up-converter, and configured to receive the digital signal and to convert the digital signal in an analog signal; an analog filter connected to the digital to analog converter, and configured to receive the analog signal, and to output a filtered analog signal including substantially only components having frequencies in a selected one of the frequency bands; a power amplifier connected to the analog filter, and configured to receive the filtered analog signal, and to amplify the filtered analog signal; an analog to digital converter configured to receive an analog feedback signal corresponding to the amplified filtered analog signal, to sample the analog feedback signal, and to output a digital feedback signal; and a programmable digital down-converter connected to the analog to digital converter and the baseband processing unit, and configured to receive the digital feedback signal, to convert the digital feedback signal to a lower sample rate based on at least one second control input, into the feedback signal, which is provided to the baseband processing unit. a baseband processing unit configured to receive a complex input signal and a feedback signal, and to output a pre-distorted baseband signal based on said complex input signal and said feedback signal; a programmable digital up-converter connected to the baseband processing unit, the programmable digital up-converter comprising: a complex baseband tuner; a digital up-sampler; a complex channel selection filter; and a quadrature modulator, a complex baseband tuner; a digital up-sampler; a complex channel selection filter; and a quadrature modulator, wherein the programmable digital up-converter is configured to receive the pre-distorted baseband signal, and to convert the pre-distorted baseband signal into a digital signal having a spectral content which is selected based on at least one first control input received from the baseband processing unit, wherein the at least one first control input includes at least one of: filter information associated with a selected one of the predetermined frequency bands, complex tuner frequency and an up-sampling parameter associated with the selected one of the predetermined frequency bands; a digital to analog converter connected to the programmable digital up-converter, and configured to receive the digital signal and to convert the digital signal in an analog signal; an analog filter connected to the digital to analog converter, and configured to receive the analog signal, and to output a filtered analog signal including substantially only components having frequencies in a selected one of the frequency bands; a power amplifier connected to the analog filter, and configured to receive the filtered analog signal, and to amplify the filtered analog signal; an analog to digital converter configured to receive an analog feedback signal corresponding to the amplified filtered analog signal, to sample the analog feedback signal, and to output a digital feedback signal; and a programmable digital down-converter connected to the analog to digital converter and the baseband processing unit, and configured to receive the digital feedback signal, to convert the digital feedback signal to a lower sample rate based on at least one second control input, into the feedback signal, which is provided to the baseband processing unit.