DIGITALLY MODULATED RF AMPLIFIER SYSTEM HAVING REDUCED INTERMODULATION ENERGY AT RF CHANNEL EDGES

摘要

A digitally modulated RF amplifier system having improved adjacent sideband distortion reduction at spaced apart frequencies located essentially at the edges of a desired frequency channel. The system includes a digital modulator that receives a digital information signal and modulates a received RF carrier signal with the digital information signal to provide a digitally modulated RF signal within a first RF channel having a bandwidth of N and which is interposed between and is adjacent to second and third channels each having bandwidth N. A non-linear power amplifier has an input that receives and amplifies the modulated RF signal and exhibits the characteristic of normally providing unwanted intermodulation energy at frequencies at the edges of the first RF channel and that extend into the adjacent second and third frequency channels. A transmission line matcher is interposed between the modulator and the power amplifier to optomize the inpurt return loss of the power amplifier. The transmission line has a length chosen to simulaneously maximize the return loss at first and second frequencies located essentially at the edges of the first frequency channel to reduce said unwanted intermodulation energy simultaneously at the edges.