Digitally coded carbon ink based reflective surface (RS) for anomalous reflection

Abstract In this paper, we propose the design of a 1-bit digitally coded resistive carbon ink-based reflective surface (RS) for achieving anomalous reflection-based beam steering. The proposed surface operates within the industrial, scientific, and medical band at 5.8 GHz (5.5–5.9 GHz). The unit cell features a simple structure consisting of a bottom metal layer, an FR-4 substrate, and a carbon ink patch on top of a polyimide layer. The polyimide layer, positioned between the patches and the FR-4 substrate, enhances the durability of the structure. The RS achieves a 1-bit phase shift resolution by varying the size of the patch, with a 10 mm patch serving as element-0 and an 11.5 mm patch as element-1. At 5.8 GHz, these two patch sizes produce a perfect 180 ∘ phase difference. The sheet resistance of the carbon ink is optimised to 3 Ω/sq to ensure high reflectivity. The patches are fabricated using a cost-effective screen-printing technique and are characterised for morphology using field emission scanning electron microscopy (FESEM) and surface roughness. A <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>16</mml:mn> <mml:mo>×</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math> array with dimensions of 320 mm × 200 mm is developed and tested for two configurations. The first configuration redirects the beam to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>θ</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>20</mml:mn> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , while the second is towards <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>θ</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>32</mml:mn> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . The proposed surface exhibits a maximum gain of 15.5 dBi with a side lobe level (SLL) of −9.2 dB for pattern-1, and a gain of 14.4 dBi with an SLL of −7.9 dB for pattern-2, maintaining stable performance over a 400 MHz bandwidth. Experimental validation includes radiation pattern measurements and received signal power. The RS-enhanced signal strength is further validated through comparison with the theoretical free-space path loss model. Additionally, the proposed RS mitigates angular non-reciprocity, ensuring consistent performance in time division duplex wireless communication systems.