The quadrature modulator approach to digital radio transmission requires a linear RF power amplifier which creates a design conflict between improving power efficiency or maintaining amplifier linearity.
Additional problems with linear RF power amplifiers, including device parametric restrictions, temperature instability, power control accuracy, wideband noise and production yields are also common.
In a polar modulation system, the power amplifier input signal may vary only in phase.
Thus a polar modulation system allows the use of highly non-linear power amplifier architectures such as Class E and Class F. In order to create the polar signal, the phase transfer of the amplifier must be known over at least a 17 dB amplitude range.
Polar modulation was originally developed by Thomas Edison in his 1874 quadruplex telegraph – this allowed 4 signals to be sent along a pair of lines, 2 in each direction.