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This paper presents a new way of designing multi-mode switchable power amplifier without relying on any extra tuning elements. By operating the RF GaN transistor as a switch (digital) or amplifier (analog), it enables three different modes within a quadrature-balanced load-modulation architecture, including series/parallel Doherty and hybrid load modulated balanced amplifier (H-LMBA), which can be optimally configured according to different load conditions. Based on this new method, an intrinsically mode-switchable load-modulation PA is designed with GaN transistors and branch-line quadrature coupler at 1.7 GHz. Together with the unique harmonic-tuned method, the nominal mode of H-LMBA (for matched condition) achieves a high-order load modulation with > 62% measured efficiency across a 10-dB output back-off (OBO) range. Efficient performance is also demonstrated at series/parallel Doherty modes, which are configured with exchangeable main/auxiliary roles and dedicated switch settings offering mismatch resilience. 

A novel highly miniaturized wideband quadrature hybrid using slow-wave technology is proposed in this paper. In order to reduce the size of conventional branch-line/coupled-line couplers, a unique structure is utilized based on two layers of crossing strips with densely interconnecting vias. This structure makes full use of the electrical coupling and magnetic coupling in the slow-wave structure, and enhances the mutual inductance effect between parallel vias, which successfully leads to enhanced coupling strength that enabling the wideband 3-dB quadrature hybrid. Importantly, 99.4% of size reduction has been achieved as compared to conventional three-section branch-line counterpart while maintaining an equally good performance. The achieved relative planar area is only 0.003A2, which is orders-of-magnitude improvement over state-of-the-art. 

This paper presents a novel reconfigurable quasi-balanced Doherty power amplifier (QB-DPA) with wide bandwidth and strong resilience to load mismatch. By leveraging the complementarity of reciprocal main/auxiliary setting and parallel/series modes, we demonstrate the first-ever broadband mismatch-resilient QB-DPA. To validate the proposed theory, a broadband 1.55-2.7-GHz QB-DPA is developed using GaN technology and 3-section branch-line coupler. With matched load, the experimental results exhibit an efficiency of 57-80% at peak output power and 49–71 % at 6-dB output back-off (OBO), respectively. Modulated measurement using a 20-MHz LTE signal with 10.5-dB peak to average ratio (PAPR) shows a 44–51 % average efficiency across the operation bandwidth and up to −36 dB ACPR. More importantly, a consistent output power and improved efficiency at OP 1dB are experimentally maintained through the parallel/series modes reconfiguration at 2: 1 voltage standing wave ratio (VSWR).