In this letter, characterization of circular highimpedance surfaces (HISs) is investigated. The reflection phase characterization used for rectangular HISs is here extended to circular lattices. Circular HISs discussed in this letter present a 2-D periodicity, and consequently the phase diagram is determined for concentric and radial polarizations. The effect of mapping a rectangular HIS into a circular one is investigated in order to give some insights regarding the design of such metasurface. The presented characterization constitutes a useful tool for the design of low-profile antennas using HIS as reflector.