Dual-Input Digital Predistortion of Millimeter-Wave RF Beamforming Arrays Driven by Two Non-Contiguous Intra-Band Signals
This paper proposes a dual-input single-output (DISO) digital predistortion (DPD) scheme to mitigate the nonlinearity in millimeter-wave RF beamforming arrays when driven by two non-contiguous intra-band signals. Starting from a pass-band Volterra series expression, the paper derives a complex baseband DISO DPD model to linearize the behaviour of RF beamforming arrays under such multi-carrier signal excitation. The proposed DPD scheme is then validated in measurements on a 64-element array driven by two 200 MHz orthogonal frequency-division multiplexing signals centered at 27.5 GHz and 28.5 GHz, and configured to radiate two simultaneous beams to serve two users located at θ = -20° and θ =18.5°, respectively. Measurements show excellent linearization results allowing for an increase in effective isotropic radiated power by more than 4 dB compared to no DPD while maintaining an error vector magnitude lower than 2% and an adjacent channel power ratio higher than 41 dBc in both frequency channels.