Sequential LMBA Design Technique for Improved Bandwidth Considering the Balanced Amplifiers off-State Impedance

This work proposes a design technique to improve the bandwidth of sequential load-modulated balanced amplifiers (SLMBAs). It is theoretically demonstrated that a finite off-state impedance of the balanced power amplifiers (BPAs) degrades the overall SLMBA performance, especially between the two efficiency peaks, i.e., when the BPAs start to operate. Moreover, it is shown that this issue is especially important when high-power devices are considered. The new proposed design technique optimizes the load trajectory of the BPAs, by properly designing their output matching networks, considering the actual off-state impedance. The method avoids the use of the conventional narrowband compensation offset lines strategy, being able to obtain optimum efficiency and output power performance when the BPAs are turned on across wide bandwidths. The proposed design technique is explained and validated with a practical 1.3-2.1-GHz 200-W GaN HEMT-based SLMBA prototype.