Effect and adaptive correction of impedance mismatch between antenna and power amplifier on digital predistortion

Digital predistortion (DPD) is a powerful and cost-effective technique to linearize Power Amplifier (PA). In radio-frequency emitters, the PA and antenna are contiguous and impedance mismatch between the two is likely to occur during emission. DPD linearization performances may be seriously degraded as a result. In this paper, firstly, we propose a new model representing the effects of impedance mismatch between PA and antenna block on the feedback signal that is measured with a coupler to adapt the predistortion. That model takes into account the coupler directivity. Secondly, we study the effect of antenna mismatch on adaptive predistortion and thirdly we propose a solution based on an adaptive correction gain to preserve linearization performances under mismatch conditions. These proposals are evaluated and validated on signals from a 120 W Doherty PA.