UCLA

The development of simultaneous transmit and receive (STAR) architectures necessitates advancedreceiver isolation techniques to handle the growing demands for frequency agility and RF bandwidth while safeguarding sensitive front-end components. One key challenge in these systems is mitigating self-interference, which can significantly degrade performance. Self-interference cancellation (SIC) has emerged as an effective solution to suppress leakage signals, facilitating full-duplex operation in a wireless system. In this work, a novel adaptive self-interference canceller has been developed using a unique transversal filter architecture for true time delay cancellation. This new design addresses the inherent architecture losses found in traditional transversal filters, thereby achieving tremendous flexibility and therefore, superior cancellation performance in multiple path scenarios with strong leakage signals. The innovation lies in replacing conventional amplitude and phase weighting components with tunable reflective discontinuities. This approach enables the implementation of fundamentally lossless passive methods for leakage signal cancellation, which significantly enhances the dynamic range and spectral efficiency of STAR systems, especially in space-constrained environments. Parallel to advancements in SIC for STAR systems, the integration of Electrically Small Antennas (ESAs) in high-bandwidth communication systems presents another significant challenge. Space constraints in deployable systems, governed by the sizes that are smaller than 0.1λ, limit the radiation bandwidth of an ESA. The effectiveness of an ESA’s efficiency-bandwidth product is directly related to its quality factor as defined by Chu’s Limit. Despite these limitations, there is a growing need for ESA integration in applications in cellular networks, biomedical implants, unmanned aerial and underwater vehicles, and internet-of-things devices, where required conventional antenna dimensions that comparable to the wavelength of operation are impractical. To address performance trade offs set by space constraints, an improved efficiency-bandwidth product has been demonstrated using an approach called Direct Antenna Modulation (DAM). A capacitively loaded loop antenna (CLLA), is strategically designed to radiate high-bandwidth signals through a precisely synchronized time-varying antenna impedance boundary condition. To effectively implement synchronization, the CLLA employs a dual-pole dual-throw (DPDT) switch configuration with high figure of merit (FoM) transistors. This novel DAM topology enables the ESA to radiate high-bandwidth phase-modulated signals efficiently, despite its defined size constraints. Compared to a time-invariant CLLA of the same form factor, the DAM implementation significantly enhances the efficiency-bandwidth product by minimizing the impact of switch technology efficiency while maintaining DAM synchronization. Overall, these advancements in adaptive self-interference cancellation and efficiency-bandwidth product of an ESA design through DAM contribute to the enhancing performance of our next generation wireless systems with maximal flexibility in platform integration.