This work presents the utilization of square ring slots as resonators on active and passive metasurfaces operating within the K a-band. Thereby, fully functional prototypes of reflectors and lenses based on a two-layer printed circuit board were fabricated and verified. The analytical model of the square ring slot structure is depicted extensively, which allows finding simulation optimized designs that can be applied to the passive prototypes. Additionally, the gained information on self-resonances is used for combinations with layers, activated through lumped varactor diodes. In the end, the reflection and transmission parameters of single active and passive designs as well as beam patterns of the lenses are measured and interpreted, resulting in a switching dynamic range of 15 dB at a bandwidth of 1 GHz for active reflectors and a maximum gain of 22 dBi at 26 GHz for the passive lens.