In this thesis work, a single layer multimode concentric circular microstrip patch antenna with reconfigurable radiation patterns is designed and investigated. The antenna consists of three radiating modes TM__, TM__, and TM__. These modes can be controlled in term of amplitude and phase to achieve radiation pattern reconfiguration. In addition, the antenna was designed on a single substrate layer fed in with 50 Ω SMA connectors. The baseline for each of the individual modes has been established with the single mode design patches. Next, single mode design parameters are used to develop the multimode single layer patch antenna. Their simulated impedance matching, gain pattern, and also the surface current distribution are very well matched with the multimode patch. Optimization and parametric studies of the multimode patch's slot spacing and also the feed locations have been studied and the best design parameters are obtained for the triple mode patch. This optimized triple mode patch design is verified for its mode characteristics, circular polarization, beam scanning, and phase center characteristics. The results show matching performance, good circular polarization performance for the TM__ mode, and limited beam scanning in one plane. Finally, the triple mode patch was fabricated on a squared ground plane. It is measured in the SDSU's Antenna and Microwave Laboratory. The impedance matching, mode, radiation patterns and beam scanning characteristics are verified which matches with the simulated results.