In this paper, the properties of a Single Negative (SNG) planar metamaterial are analysed, designed and measured. The Single Negative structure is made of Spiral Resonators printed on a thin dielectric layer. The analysis is based on an analytical modelling using equivalent circuits. This approach enables to explain the origin of multiple resonant frequencies in Single Negative Metamaterials. The calculations are successfully validated by measurements carried out in the frequency range [80 - 150 MHz]. These properties lead to very interesting applications, such as compact antennas with high directivity or enhancing of magnetic resonance imaging resolution.