Phase-Aware Radiation Patterns for Accurate Orientation Optimization of Rotatable Arrays

Rotatable antennas (RA) expand the spatial degrees of freedom of multiple-input multiple-output beyond conventional fixed antenna systems. However, many evaluations model rotation only as a scalar gain modulation and ignore the phase embedded in element radiation patterns. This paper addresses that gap by developing a rotation-explicit, phase-aware channel model based on electromagnetic full-wave radiation patterns that preserve both amplitude and phase. On this foundation, we maximize multi-user multiple-input single-output downlink sum rate by optimizing per-antenna orientation angles with a feasible-direction method, while zero-forcing precoder is used to mitigate the inter-user interference. Our Simulations show that, under both uniform and hotspot user distributions, the phase-aware RA model yields more accurate orientation optimization and, consequently, higher achievable sum rate than the magnitude-only model. These results underscore the necessity of incorporating element-pattern phase in rotation-aware system design and evaluation.