Mitigating Quantization Lobes in mmWave Low-bit Reconfigurable
Reflective Surfaces
Abstract
We present a method for the mitigation of quantization lobes in
single-bit reconfigurable reflective surfaces (RRSs). Typically, RRSs
are planar beamforming structures consisting of hundreds or thousands of
antennas with integrated tunable switches. Under plane-wave
illumination, single-bit RRSs suffer from undesired side lobes or
quantization lobes, which are caused by the periodicity of the errors
due to the limited number of bits used in phase quantization. In this
work, we present a topology that suppresses the quantization lobes using
single-layer, 1-bit RRSs, by implementing a fixed but random phase delay
in every unit-cell. The introduction of phase randomization breaks the
periodicity of the quantization errors, thus reducing the quantization
lobe level (QLL). We carry out a theoretical analysis to demonstrate the
effect of phase randomization in RRSs, and for the first time, provide
the condition for choosing the range of randomization required to
achieve the lowest sidelobe level (SLL). Leveraging this condition, we
design a single-layer, 1-bit 30×30 randomized RRS at 222.5 GHz. The
reflective surface is fabricated on a thin, low-loss alumina ribbon
ceramic wafer from Corning Inc. using a simplified fabrication technique
suitable for large-scale production of mmWave/THz RRSs. Finally, we
present the radar cross-section (RCS) characterization results obtained
from a quasi-optical measurement setup validating the mitigation of
quantization lobes using the proposed randomization technique.