In recent years, there has been constant growth in using gigahertz frequencies for various applications. The state of the art of antenna integration with passive circuits techniques offering increased cut-off frequencies, open up new opportunities for integrating systems along with an antenna for either Transmit/Receive application. The work carried out in this book mainly deals with the survey of antenna structures which are compatible to integrate with passive circuits for microwave as well as millimeter/sub-milliliter wave applications. Lot of research in the field of passive receiver front-end design is being carried out. This work covers three aspects of passive receiver front-end design. The first is the analysis and design of new wide-band high gain micro-strip antennas, the second aspect is the design of compact high performance low-pass and band-pass filters and the third aspects is to integrate antenna and filter into single substrate.