Millimeter-wave electronically scanned reflectarray optimization and analysis

Abstract

The development of millimeter-wave scanning reflectarrays and phased arrays provides an important path to enabling electronic scanning capabilities at high frequencies. This technology could be used to eliminate the mechanical scanners that are currently used with radar imaging systems. In this work, we analyze properties of wafer-scale two-dimensional rectangular lattice arrays that can be used with a confocal imager for 220 GHz electronic scanning of meter-sized fields of regard at 50 m. Applications include covert imaging of hidden anomalies. We examine tradeoffs between overall system size and array complexity and analyze properties of reflectarrays compatible with a system design that was chosen based on these considerations. The effects of phase quantization are considered in detail for arrays with 1- and 2- bit phase shifters and the results are compared in terms of impacts to image quality. Beam pointing accuracy, main beam energy fraction, and the number and intensity of quantization lobes that appear over the scan ranges of interest are compared. Our results indicate that arrays with 1- and 2-bit phase quantization achieve similar main beam energy efficiencies over the desired scan range. Without restricting the scan range, 1-bit phase quantization is insufficient, resulting in maximum errors that are comparable to the required minimum scan angle. Two-bit phase quantization is preferable, resulting in pointing angle errors of at most 15 % of the diffraction-limited beam-size. Both 1- and 2-bit phase quantization cases result in lobes appearing above our threshold, indicating that spurious returns are a problem that will require further attention.