Joint Baseband Waveform and Reactance Co-Design for Single RF Electrically Steerable Parasitic Array Radiator Aided Integrated Sensing and Communication

In this letter, we propose an integrated sensing and communication (ISAC) system based on an electronically steerable parasitic array radiator (ESPAR) antenna that employs a single-radio frequency (RF) chain. By jointly designing the baseband transmit waveform and the dynamic reactance profile of the parasitic elements over time, the proposed system exploits mutual electromagnetic coupling as a spatio-temporal synthesis degree-of-freedom (DoF). We formulate a non-convex co-design optimization problem that minimizes the mean square error (MSE) between the achieved and desired radar transmit beam patterns while satisfying the signal-to-interference-plus-noise ratio (SINR) requirements of communication users (CUs), varactor reactance tuning limits, slew-rate hardware constraints, and transmit power constraints. To solve the problem, we develop an alternating optimization (AO) framework that combines majorization-minimization (MM) and convex relaxation techniques. Numerical results confirm that the single-RF-chain ESPAR-based ISAC architecture achieves promising dual-functional sensing and communication performance while significantly reducing hardware complexity and power consumption compared with conventional multi-RF-chain digital array system.