I. Introduction
In modern wireless communications systems, due to spectrum efficiency reasons, modulated signals with high peak-to-average power ratio (PAPR) are commonly used. This imposes the use of radio frequency power amplifiers (PAs) with improved efficiency at higher output power back-off (OBO) levels. Over the years, exactly to tackle this problem, several advanced PA architectures, using the load-modulation concept, were presented such as the Doherty PA (DPA) [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], outphasing topologies [16], [17], [18], [19], and the recently proposed load-modulated balanced amplifier (LMBA) [20], [21], [22], [23], [24], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41].