Experimental Characterization and Empirical Beam Steering Analysis of a 28 GHz 1-Bit 8x8 RIS Reflectarray via Conductivity Pattern Modulation

This work investigates the beam steering capabilities of a small-to-medium-sized Reconfigurable Intelligent Surface (RIS) consisting of an 8×8 array of simplified 1-bit reflective unit cells operating at 28 GHz. Each unit cell is composed of two rectangular patches connected by a single PIN diode, forming a compact and fabrication-friendly design that omits vias and complex bias circuitry. The array is illuminated under normal incidence by a vertically oriented horn antenna, and various binary ON/OFF control patterns are applied to modulate the reflectivity states of the unit cells. The resulting far-field radiation patterns are measured experimentally to assess the extent to which the direction of the main lobe can be steered solely by modifying the conductivity pattern across the surface. Particular emphasis is placed on identifying empirical rules that relate the spatial geometry of the applied patterns to the observed beam direction. The results demonstrate that even modest-sized RIS arrays can achieve effective beam steering through appropriately structured binary control, offering insight into low-complexity RIS design strategies.