This book describes the basic theory of Microstrip patch antenna, Slot antenna, Resonant Cavity. Content wise this book divided in two techniques from which the gain, impedance and front to back ratio is improved. It describes the basic nature of microstrip patch antenna feed by waveguide, slot coupling module to investigate the behavior of resonant nature of cavity and coupling nature of slot and finally slot radiators backed by cylindrical cavity. Fabrication and measurements is carried out to prove the proposed geometry. The achieved results show very good agreement with simulated results.