The objective of this study was to determine the perturbation of the radiation pattern of a slotted cylinder antenna due to the presence of one or more obstacles on the conducting cylinder. The obstacles of particular concern are one or more long axial conducting columns whose height is small compared to a wavelength. The study, incorporating three different methods as outlined below, was specifically used as a partial evaluation of the radiation pattern of a microstrip antenna array mounted on the Plasma Diagnostics Package (PDP) satellite. (1) An analytical approach to evaluate the near and far-field enabled us to determine the sensitivity of the far-field pattern with respect to the positioning of these axial columns around the cylinder. It also provided the fields needed to evaluate the currents induced on the columns. (2) An experimental investigation was conducted on a half-size scale model of the PDP to verify the analytical method. This was done inside a microwave anechoic chamber. (3) A numerical method was the third approach used to analyze this problem. The NEC (Numerical Electromagnetic Code Method of Moments) was modified for application to this radiating structure, and the resulting computer program was utilized in predicting the effect of the axial columns on the far-field pattern;The results of all three methods provide the same conclusions about the influence of the columns on the far-field pattern. Each of the methods verified the sensitivity of the patterns to the positioning of the columns as predicted by the near-field computation.