A Comparative Study on Ray-Tracing and Physical-Optics Methods for the Analysis of Transmitarray Antennas

This study compares the accuracy of two semi-analytical methods based on ray tracing (RT) and physical optics (PO) for the analysis and design of transmitarrays of different sizes. The assessment considers multiple focal-to-diameter ratios and eight unit cells implementing 3-bit uniform phase quantization at 30 GHz. The results, validated by full-wave simulations, demonstrate that both the RT and PO methods yield excellent agreement in standard-profile configurations. However, the RT approach, which assumes the transmitarray to be in the far-field region of the primary feed, provides a wrong evaluation of the gain of low-profile antennas, with errors up to 1.5 dB at 34 GHz. In contrast, the PO method accounts for near-field effects and accurately predicts the transmitarray performance even when the focal distance is comparable to the wavelength. Additionally, the PO method enables the analysis of large antennas with computational efficiency comparable to RT, requiring approximately four minutes for transmitarrays with diameters of 30 wavelengths.