A modeling methodology is proposed for characterizing the reflection coefficient S11( f ) of narrow band antennas undergoing random disturbances. Firstly, identification techniques are used to get a parsimonious representation of the S11; then the Polynomial Chaos Expansion (PCE) method is used to characterize quantitatively the influence of random disturbances on the compressed S11. The derived S11 model can be used as efficient surrogate for statistical analysis of antennas’ frequency behavior. We have applied the proposed methodology to two narrow band antennas – a deformable dipole and a textile patch – in order to demonstrate its performance. Models with good accuracy have been derived for both cases.