Abstract

A recent advancement introduced a prephased reflective metasurface (MS) using 1-bit control to suppress the quantization lobe (QL) inherent in a typical 1-bit MS under plane wave incidence, particularly in millimeter and sub-millimeter wave bands. However, the optimal method for prephasing using random phases has not been fully explored. This study investigates the optimal number of prephasing, which denotes the number of discrete random phases for effective QL suppression while ensuring low design complexity. The results indicate that employing four discrete phases, equally spaced at 45°intervals, is optimal. The random phases with a 45°separation are implemented into four pairs of unit cells with ON/OFF control using multilayer PCBs at 140 GHz. The unit cell consisted of a metallic patch coupled with a transmission (Tx) line through a slot, with passive ON/OFF switching embedded inside the Tx line for 1-bit reflection phase control. Finally, three MSs are designed and fabricated, each configured to reflect a plane wave under normal incidence to three reflection angles (θr) of 15°, 30°, and 45°at 140 GHz. Each MS comprises 30 × 30 unit cells implemented with fixed random prephases. Measurement results reveal significant reductions in QL up to −20 dB, with a near 25% reflection efficiency and more than 10% 3 dB gain bandwidth at 140 GHz in the sub-millimeter wave band.