Comparisons of Scalar and Tensor Circularly-Polarized Holographic Artificial Impedance Surfaces

In principle, both scalar and tensor holographic artificial impedance surfaces (HAISs) can generate circularly-polarized waves. It is found, however, the previously-reported works on circularly-polarized holographic antennas are based on tensor impedance surfaces. This paper studies the generations of circularly-polarized waves by using scalar and tensor HAISs, and compare their performance in terms of design complexity, impedance bandwidth, 3dB axial ratio (AR) bandwidth, realized gains, etc. The mechanisms of producing circularly-polarized waves using scalar and tensor HAISs are first formulated and presented. Two right-hand circularly-polarized holographic antennas are then implemented with the scalar and tensor HAISs, respectively, and simulated. The simulations conclude that the tensor HAIS indeed outperforms the scalar HAIS in generation of circularly-polarized waves. In particular, the peak gain of the tensor HAIS is much higher than that of the scalar HAIS. The conclusions obtained in this paper give a clear answer on designing circularly-polarized HAISs with good performance.