Modern houses use energy efficient building materials like metal shielding and energy saving windows to improve the thermal efficiency. Such energy efficient building mate-rials creates the barrier for outdoor-to-indoor RF signals propagation which is one of the challenging problems in the field of cellular communication. In order to solve such problem of outdoor-to-indoor propagation, an effective and efficient solution is very essential. Some existing techniques to solve the indoor coverage problem are the use of outdoor to indoor repeaters, pico-cell or dedicated indoor systems like distributed an-tenna system and radiating cables. However, such techniques are operator oriented; ex-pensive for single residential houses; possess additional network architecture design and maintenance complexity. One of the newer passive techniques which is operator inde-pendent and does not have additional network burden, is the use of frequency selective windows. Frequency selective windows consist of Frequency Selective Surface (FSS) etched on the metal coating of the energy saving windows, allowing cellular frequencies to pass through them while blocking the thermal radiation. FSS is the combination of either conducting patches or apertures in a thin conducting sheet arranged periodically in one or two dimensional array. FSS possess frequency selective behavior based on the element geometry. Patch type of FSS exhibits total reflection around resonant frequency whereas aperture type exhibits total transmission. This thesis presents the modelling, simulation, fabrication and test measurements of the FSS that is transparent to GSM and UMTS frequency band. FSS with a double square loop aperture as a unit cell is selected for the analysis. The modelling and simu-lation of the FSS are carried out in the Computer Simulation Technology (CST) micro-wave studio, 2012 version. FSS prototype is fabricated using the commercial available aluminum foil. Furthermore, the FSS prototype is tested in the laboratory as well as in real-time networks. The real-time or field measurement is conducted in the real networks for all three operators of Finland, namely DNA, Elisa and TeliaSonera. The laboratory result shows the resonant frequency shift downwards by a factor of 1.22 comparing to the simulation results of freestanding FSS. The reason behind such frequency shift is well explained by the presence of a dielectric substrate in FSS prototype. On average, for all operators the field measurement result shows the transmission improvement of around 10 dB and 4.5 dB in GSM and UMTS band respectively over the plain aluminum foil. Although the field measurement result does not show much improvement compared to the laboratory measurement result, it still prevails the possibility of using FSS for indoor coverage improvement.
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