The aim of this paper is to present different ways to extract electrical models of an antenna specifically designed for Radio Frequency IDentification (RFID) Ultra High Frequency (UHF) communications. More precisely the models are extracted from a helical dipole designed to operate in the European RFID band and in the context of smart textiles. This kind of antenna was chosen because its electrical properties and radiation pattern are relatively robust with respect to stretching deformation. After presenting the antenna's design, two strategies to extract antenna models are discussed and then compared. The first method is taking into account the antenna's physical dimensions and shape, and the second one, which is a general method relevant to any other antenna geometry, is based on the rational approximation of the antenna's frequency response.