Authors
Nathan Golding, Zoya Popovic, and Laila Marzall (University of Colorado Boulder)
Abstract
The rapid growth of wireless communications and the increasing congestion of the electromagnetic spectrum demand advanced hardware platforms that enable efficient spectrum sharing. This work presents the design, implementation, and experimental validation of a digital phased-array demonstrator developed within the SpectrumX Flagship 1 framework, operating in the 7–8.4 GHz band. The system adopts a mixed-signal architecture that integrates antennas, an RF front-end, high-speed data converters, FPGA-based processing, and digital beamforming. The study emphasizes practical limitations in phased-array systems, demonstrating that performance degradation is primarily driven by non-idealities in the RF and mixed-signal chain, including phase and amplitude errors, channel mismatch, local oscillator phase noise, IQ imbalance, timing jitter, and nonlinearities. To address these challenges, adaptive beamforming techniques are implemented to suppress interference via spatial nulling. Algorithms such as minimum variance distortionless response (MVDR), linearly constrained minimum variance (LCMV), and sector-based approaches are evaluated and compared in a hardware testbed. A comprehensive calibration framework combining digital multi-chip synchronization and over-the-air (OTA) RF calibration is developed to restore phase and amplitude coherence across channels. Experimental results obtained from anechoic chamber measurements demonstrate recovery of expected array patterns and significant improvements in signal-to-interference-plus-noise ratio (SINR), increasing from approximately −5 dB prior to beamforming to greater than 10 dB after processing. The presented demonstrator provides a scalable, portable platform for real-world spectrum-sharing experiments and establishes a foundation for future research on full-duplex systems, adaptive interference mitigation, and integrated communication and sensing applications.