Comparative analysis of dual-polarized varactor loaded Reconfigurable Intelligent Surfaces

A comparative analysis of different varactor loaded RIS elements is presented. In particular, three dual polarized element topologies are compared by selecting the same substrate properties and the same tunable lumped elements. It is shown that the elements are characterized by two resonances where the phase response can be controlled. The fundamental resonance is typically characterized by low loss with respect to the second resonance. However, at the first resonance, the unit cell is smaller in terms of wavelength with respect to the second resonance. This implies higher number of varactors diodes are necessary to control the RIS with a consequent increase of the cost.