Evaluation of the phase discretization effect in transmitarrays formed by sub-wavelength patches

Abstract

Most of the transmitarray phase shifting cell designs assume a periodic repetition of the same cell to account for the coupling effects of the neighboring cells. However the behavior in terms of magnitude and phase of the transmission coefficient calculated in this way may change when the neighboring cells have different phase, as normally happens in transmitarrays due to phase discretization. This paper characterizes this effect using a family of sub-wavelength patch cells covering the entire 360º phase shift interval, all with transmission coefficient better than -0.2 dB in the periodic structure. A stepped-phase structure is analysed considering different phase step values from 5º up to 90º. It is shown that the magnitude of the cells transmission factor changes considerably at the transition between different elements, with the unit cells with higher phase shift showing increased transmission while the lower phase shift cells in the transition tend to block the transmission more.