The Federal Communications Commission recognizes the need for the wireless industry to explore the 28-95 GHz millimeter-wave (mm-wave) bands where wider bandwidth is available, and future allocations may reach above 100 GHz. This explosion of mm-wave bandwidth opens up applications in 5G wireless systems spanning communications, localization, imaging, and radar. This project addresses fundamental scientific and engineering challenges in generating multiple parallel radio "beams" at mm-wave frequencies. A radio beam refers to a directional channel that establishes point-to-point contact for wireless communications and remote sensing. The ability to form a large number of such radio beams with high bandwidths will tremendously improve the performance for next-generation wireless systems. For example, multiple beams are essential for achieving the orders-of-magnitude increases in capacity, data rate, and geographical penetration required by the explosive growth in wireless applications. Moreover, they are important for both transmitters and receivers. The project will draw on an analogy between the spatial Fourier transform and a thin optical lens to obtain multiple wideband beams. Unlike lens-antenna-based approaches in the literature, this project will use a planar aperture antenna in conjunction with analog integrated circuits to generate many wideband mm-wave beams subject to power and size constraints. The proposed highly integrated approach is attractive for mobile applications including 5G smart devices, the internet of things, mobile robotics, and unmanned aerial vehicles, and other emerging applications focused on mm-waves. In addition to scientific research, the project will ensure that both minority students and female students will be mentored towards careers in mathematics, communications, as well as microwave circuits and systems. Educational materials will be developed for teaching array signal processing, microwave integrated circuit (IC) design, and ultra-high-speed analog signal processing. Principal Investigators (PIs) Madanayake and Mandal will organize a mini-conference to enhance microwave and mm-wave research activities at nearby universities in northeast Ohio. PI Madanayake will collaborate with co-PIs towards mentoring underrepresented students towards careers in Science, Technology, Engineering, and Math (STEM). The proposal team is uniquely placed to promote STEM topics spanning both electrical engineering and mathematics domains. The project will lead to education of the wider community on the importance of cross-disciplinary collaboration. Further, the team will strive to show the importance of learning deeper math topics towards success in technology and engineering careers.A multi-beam array receiver is deeply difficult to realize in IC form due to the underlying complexity of its signal flow graph. In this work, mathematical methods based on the theories of i) sparse factorization of structured complex matrices, and ii) approximate transforms are proposed to solve this problem. The resulting matrices are realized with multi-GHz bandwidths using analog ICs. One of the intellectual contributions is the development of efficient wideband beamformers based on sparse factorizations of delay Vandermonde matrices (DVM). This DVM algorithm solves the longstanding "beam squint" problem, i.e., the fact that the beam direction changes with input frequency, making true wideband operation impossible. Another is the derivation of transform matrices with specified properties that approximate the discrete Fourier transform (DFT). Such approximate transforms are not subjected to the known computational complexity bounds of the exact DFT, and approximate-DFT-based multi-beamformers can in fact be efficiently implemented using current-mode analog ICs. Finally, precision circuit design, digital calibration, built-in self-test, and other methods will be explored for efficiently realizing the proposed multi-beamforming networks in analog IC form.
