Transmitter linearisation techniques for the 1.5-1.7 GHz MSAT bands

The two favoured modulation techniques for MSAT ACSSB and filtered QPSK, both exhibit a non-constant envelope, and thus require linear amplification to avoid undue spectral spreading into adjacent channels. Transmitter linearity is not easily achieved at these frequencies. The authors address this problem through the application of feedback control techniques to improve the linearity of the entire transmitter system incorporating the nonlinear amplifying element. It is shown that with appropriate choice of feedback structure, it is possible to improve the linearity of Class C amplifier stages to give superior performance to those of uncompensated Class A devices, thus greatly improving the transmitter power efficiency and reducing component cost