A broadband polynomial predistorter for reconfigurable radio

An analogue polynomial predistorter working at RF is presented. It is capable of operating at multiple frequency bands over a wide linearisation bandwidth. These are important features for a reconfigurable radio application. The technique approximates the inverse of the amplifier transfer function up to third-order (cubic) nonlinearity by using polynomial functions. Theoretical analysis shows that the performance of the technique is limited more by the generation of additional fifth-order IMD (IM5), than the gain and phase matching of the predistorter. The measured two-tone tests at different frequency bands show 13 dB suppression of third-order IMD (IM3) is possible over 40 MHz tone separation. A 30 dB IM3 reduction can be achieved by increasing the IM5 by 9 dB. The research will continue by extending the predistorter to include higher orders of nonlinearity for a larger improvement in IMD suppression.