This article presents the analysis and investigation of the effect of loading a TEM horn antenna with a frequency selective surface (FSS) of finite size. It is simulated on FR4 (lossy) of relative permittivity 4.4, thickness 1.58mm and loss tangent 0.0035. This structure is called a filtering antenna (filtenna). Basically it is applied for filtering and minimizing the interference and noise in the desired band. The filtration is carried out using a finite FSS of double square loop of overall dimensions 20mmx20mm. The structure is simulated using CST MWS.