The migration of telecommunication services and radar systems to Millimeter-wave (MMW) frequencies (30 to 300GHz) leads to the necessity of researching for alternative fabrication technologies and materials rather than the used for microwave frequencies. Part of this thesis work is focused in three MMW band applications such as Satellite Communication Systems (SCS) at Ka-band,Wireless Personal Area Network (WPAN) at V-band and Automotive Radar at W-band. In these applications, where the antenna is part of a mobile device, it is targeted the use of planar antennas because their low profile and low fabrication cost, together with reconfiguration capability and low losses. This book presents a study of materials, transmission lines geometries and switches in the MMW frequency band. The fabrication tolerances have also been studied, analyzing the variations in the final antenna parameters. The tolerances, together with the materials and antenna dimensions lead to the use of microfabrication processes. Finally, two different pattern reconfigurable antenna designs operating at Ka-, V- and W-bands are presented as a demonstration.