With the increasing demand for faster date rates and extensive user connectivities, the complex modulation schemes and large-scaled arrays have been widely researched and employed in the modern wireless links e.g., 5G and beyond-5G systems. These pose major challenges to design the power amplifiers (PAs) to accommodate the system level evolution. As the critical part, the power amplifiers (PAs) dominate the output power, efficiency, linearity and reliability of the radio frequency (RF) transmitter. Consequently, the PA's capability of maintaining an efficient, linear and reliable signal amplification operation is essential to the communication systems. On the other hand, due to the deployment of massive multiple input/multiple output (MIMO) technique, the highly integrated active antenna systems replaced traditional 50Ω-based PA with sectorized antenna architectures. This brings the fact that, as the beam is steered in the antenna array, the dynamic load impedance observed from PAs can be up to 2: 1 Voltage Standing Wave Ratio (VSWR) due to the time-varying phasing and output power between the adjacent antenna elements and PAs, thus severely deteriorate PAs' performance. To resolve aforementioned challenges, a novel design theory of Quasi-balanced Doherty power amplifier (QB-DPA) is first presented in this dissertation, which opens a new vision to counteract the mismatch-induced degradation using reconfigurable PA architectures. In this QB-DPA design, the isolation port of the PA's output coupler is alternatively terminated to 50-Ω load and ground to enable the balanced and Doherty modes. With the implementation of the silicon-on-insulator (SOI)-based single-pole-double-throw (SPDT) switch to realize the reconfiguration, the physical prototype is demonstrated exhibiting remarkable DPA performance, in terms of the linearity, efficiency and output power. Subsequently, a series/parallel QB-DPA theory that not only can improve the back-off efficiency of QB-DPA, but also significantly restore the load-mismatch degradation is proposed. This novel topology includes and unifies QB-DPA modes at balanced, series and parallel Doherty, respectively. Moreover, a novel linearity-enhanced combiner is introduced for nominal 50-Ω load to improve the linearity at both series and parallel QB-DPA modes. The reconfiguration between series and parallel operations largely restore the performance degradation when the PAs suffer a dynamic antenna mismatch condition. Finally, a wideband mismatch-resilient QB-DPA is presented. Through parallel/series reconfiguration and reciprocal biasing, it is for the first time shown that the QB-DPA is able to maintain a stable output power as well as enhanced efficiency and linearity across 2 : 1 VSWR circle, and this operation can be seamlessly extended to a wide bandwidth which holds promising potential for application to array-based massive MIMO systems.
If this is your thesis or dissertation, and want to learn how to access it or for more information about readership statistics, contact us at STARS@ucf.edu
Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Electrical and Computer Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Lyu, Haifeng, "Reconfigurable Load-Modulated Power Amplifier For Energy- and Spectrum-Efficient Wireless Communications" (2022). Electronic Theses and Dissertations, 2020-. 1405.