In buildings with multiple occupancy, frequency shielding and re-use methods are required to enhance the spectral efficiency. Passive band stop Frequency Selective Surfaces (FSSs) can be used to improve the electromagnetic architecture of the buildings. This dissertation provides a new approach to the design of spatial filter material (frequency selective surfaces) on a flexible, thin and transparent substrate. The flexibility, transparency and frequency shielding property of these film type structures help them to be deployed on the walls/windows of offices, vehicles, and prisons etc. This technique is a low cost method of confining LAN pico cells in one room. A simple ring FSS of sub wavelength element size (λo/4) can provide transmission stop band at 12.3 GHz. The variation in band stop characteristics was investigated for various wall materials. The centre frequency was varied by more than 3 GHz by common wall materials. A convoluted square loop FSS was developed to miniaturize the FSS element size without changing the unit cell dimensions. The small dimensions of the elements improved the angular stability for incident angles upto 45o. A frequency reduction of 62% was achieved by modifying the traditional square loop FSS. The bandwidth increased from 2 GHz to 8 GHz using double layer FSS configurations. An offset technique was introduced in the bottom layer in order to maximize the mutual coupling between the two layers of the composite FSS structure. A meandered double layer FSS with the unit cell dimensions much smaller than the operating wavelength (λo/22) shifted the stop band frequency from 8 GHz to 1.89 GHz. The densely packed meandered design showed a stable response for the perpendicular (TE) and parallel (TM) polarizations at oblique incidence.