Phase Error Analysis of Discrete Dielectric Lens With Experimental Results at 94 GHz

This paper presents the phase error analysis of a single-layer discrete dielectric lens that uses nonresonant unit cell and can be fabricated using low-cost PCB technology. An extensive detailed study of the nonresonant unit cell is performed to understand the phase error loss mechanism and to find the best periodicity (unit cell size or interelement spacing) that produces almost the same phase response not only at different frequencies but also for both normal and oblique incidence which leads to lower oblique phase error (OPE) loss across the lens aperture and higher aperture efficiency. Unit cells of 0.47λ_{94 GHz} ≤ periodicity ≤ 0.68λ_{94 GHz} are studied and the optimum periodicity is addressed. Based on this study, three lenses of identical aperture area (100 × 100 × 6.35 mm³) but different unit cell sizes (0.5λ_{94 GHz}, 0.53λ_{94 GHz}, and 0.62λ_{94 GHz}) are designed, fabricated, and tested. It is found that the maximum OPE is reduced from about 65° to less than 25°, aperture efficiency is improved by about 13.4% at 94 GHz, and the total number of unit cells is reduced by about 42.6% when periodicity changed from 0.47λ_{94 GHz} to 0.62λ_{94 GHz}, respectively. Furthermore, lens of 0.62λ_{94 GHz} periodicity will have the highest aperture efficiency of 48.7%, gain = 37.8 dB at 94 GHz, beamwidth ≈1.2°, F/B ratio ≈37.5 dB, measured |S₁₁| <; -10 dB, cross-pol <; -27dBandoffersSLLH <; -24.3dB,andSLLE <; -18.5 dB.