CAREER: Non-Reciprocally-Coupled Load-Modulation Platform for Next-Generation High-Power Magnetic-Less Fully-Directional Radio Front Ends

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The exacerbating congestion and overcrowding of wireless spectrum strongly demand new spectrally efficient communication system architectures, e.g., full duplex and massive multi-input multi-output (mMIMO). These emerging systems necessitate fully-directional radiofrequency (RF) front-ends, which normally involve bulky and expensive magnetic devices for a critical function of signal circulation/isolation at the antenna interface. Although the non-magnetic counterparts promise chip-level integration with massive manufacturability, their very low power-handling capability remains as the bottleneck. This CAREER project aims to fundamentally unleash the high-power operation of non-magnetic non-reciprocal devices though a new paradigm of indirect signal circulation/isolation integrated into the prevailing load-modulation power amplifiers (PAs), named Non-Reciprocally-Coupled Load Modulation (NRC-LM). More broadly, this ‘indirect’ design paradigm can be generalized to other power-sensitive devices, e.g., tunable filters, acoustic-wave filters, and switches, which could enable high-power frequency-agile RF front-ends and impact the field of cognitive radios. Beyond the technological frontiers, this research will address the nation’s core interests in spectrum sustainability and ubiquitous coverage of high-speed connectivity, potentially leading to immense economic benefits. Moreover, by enhancing the efficiency of PAs (the most energy-consuming unit on all wireless platforms) with NRC-LM, the energy efficiency and environmental impacts of the entire wireless ecosystem can be improved. The impact of this research will be further expanded through several educational and outreach activities: (1) The RF/microwave curricula at the University of Central Florida will be enhanced with new class modules. (2) Diverse mentoring and outreach programs will be designed to attract students of underrepresented minority groups in STEM, thus preparing a new diverse workforce for the RF industry. (3) The engagement of undergraduate students in RF/microwave research will be promoted through a comprehensive set of intriguing efforts. (4) To stimulate interests from K-12 students and general public, a series of “demystifying wireless communications” mini lectures will be designed, exhibited in outreach activities, and disseminated on social media platforms. The objective of this CAREER project is to establish the theoretical foundation and practical design methodologies for high-power magnetic-less fully-directional RF front-ends based on NRC-LM. By leveraging a unique characteristic of active load modulation, the circulator placement is transformed from the high-power node of PA output to an inner low-power node, while maintaining the critical signal circulation/isolation behavior. This transformation not only inherently eliminates the unaffordable power stress on non-magnetic circulator but also greatly mitigates the impact of its unforgiven loss and non-linearity on the overall transmitter. The proposed research comprehensively spans over theory, design practice, and system architecture: (1) As a foundation of practical designs, the new NRC-LM theory in terms of directional transmission and reception will be systematically established and generalized to all existing load-modulation modes. (2) Moreover, mixed digital-RF design in conjunction with advanced multi-input NRC-LM transmitter architecture will be investigated to synergize an optimal cooperation between non-magnetic circulator and active LM at arbitrary in-band frequencies, pushing extreme bandwidth, efficiency, linearity, dynamic range, etc. (3) Meanwhile, a novel quadrature-commutated circulator is proposed to offer ultra-wide bandwidth, watt-level power handling, and low loss. (4) Furthermore, innovative system-level designs will be studied to integrate the NRC-LM-based front-ends into mMIMO (antenna-array-based) and full-duplex systems, which can lead to unprecedented spectrum and energy efficiencies as well as multi-band and multi-standard capabilities. Overall, the success of this research will significantly enhance the next-generation spectrum- and energy-efficient communications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.