Space–Time modulated and hardware-efficient electromagnetic platforms for integrated sensing and communication

The rapid evolution of next-generation wireless systems demands architectures capable of supporting both high-throughput communication and high-resolution sensing while maintaining hardware efficiency and scalability. Conventional phased-array systems rely on multiple RF chains, phase shifters, and mixers, leading to significant complexity, power consumption, and cost, particularly at millimeter-wave and sub-terahertz frequencies. These challenges motivate alternative paradigms that embed functionality directly into the electromagnetic radiation process rather than relying solely on conventional RF front-end architectures. This dissertation develops a unified framework for hardware-efficient electromagnetic platforms based on radiation-level modulation, direct antenna modulation (DAM), and space-time coding (STC). In the proposed approach, digitally controlled radiation states are applied directly to antennas, arrays, and metasurfaces, enabling modulation, beamforming, and spectral manipulation in the electromagnetic domain. The dissertation first establishes the principle of DAM, demonstrating multi-stream BPSK transmission using a single RF source and digitally controlled antenna states. Building on this foundation, a generalized STC framework is developed to describe harmonic beam generation, spectral-angular mapping, and energy distribution among modulation harmonics. Closed-form relationships between coding sequences and harmonic beam directions are derived, enabling deterministic harmonic beam steering and multi-beam radiation. Leveraging this framework, the dissertation demonstrates multi-target radar sensing and integrated sensing and communication (ISAC) using STC-enabled transmitting arrays. Spatio-spectral mapping is exploited for angular discrimination, angle estimation, and vital sign monitoring, enabling simultaneous multi-person detection with reduced RF hardware complexity. To overcome the discrete-beam limitations of periodic coding, asynchronous STC architectures are introduced to realize automated beam scanning and continuous angular coverage. In addition, a space-time-coded phased array (STCPA) is developed to combine harmonic beam generation with phased-array steering, enabling steerable spatio-spectral mapping for enhanced multi-target sensing. To extend these concepts toward practical high-frequency implementations, several scalable hardware platforms are developed, including a GaAs MMIC-based D-band reconfigurable metasurface, glass integrated passive device (IPD) CRLH-SIW antennas, and a sub-THz binary coding metasurface. These implementations demonstrate that the proposed radiation-level modulation framework is compatible with both compact low-frequency radiators and scalable millimeter-wave and sub-terahertz electromagnetic systems. Overall, this dissertation establishes radiation-level modulation and harmonic-domain electromagnetic engineering as viable alternatives to conventional RF front-end scaling. The presented theory, system demonstrations, and hardware implementations provide a pathway toward compact, programmable, and multifunctional platforms for future wireless communication, radar sensing, and biomedical monitoring applications.