This chapter is organized in two parts. The first part deals with the design and implementation of a microstrip antenna array with Butler matrix. The planar microstrip antenna array has four beams at four different directions, circular polarization diversity, good axial ratio, high gain, and wide bandwidth by implementing the 4×4 Butler matrix as a feeding network to the 2×2 planar microstrip antenna array. The circular polarization diversity is generated by rotating the linearly polarized identical elements of the planar microstrip antenna array so that the E-field in the x-direction is equal to the E-field in the ydirection. Then, by feeding the planar array with Butler matrix, phase delay of / 2 π ± between those two E-fields is provided. In the second part of this chapter, the analysis, design and implementation of an Aperture Coupled Micro-Strip Antenna (ACMSA) are introduced. A quadrature hybrid is used as a feeder for providing simultaneous circular polarization diversity with a microstrip antenna; but the utilization of the quadrature hybrid as a feeder results in large antenna size. In order to minimize the antenna size, the microstrip antenna is fed by a quadrature hybrid through two orthogonal apertures whose position is determined based on a cavity model theory. The size of the proposed ACMSA is small due to the use of the aperture coupled structure. The cavity model theory is started with Maxwell's equations, followed by the solution of the homogeneous wave equations. Finally, the eigenfunction expansion for the calculation of the input impedance is presented. This chapter is organized as follows. The first part deals with design and implementation of a microstrip antenna array with Butler matrix, which describe the design details of a rectangular microstrip patch antenna and a 4×4 Butler matrix. Further, analysis of planar microstrip antenna array with Butler matrix and the development of the radiation pattern for the planar microstrip antenna array are presented. In the second part, the design and implementation of an aperture coupled microstrip antenna, the analysis of ACMSA using cavity model, the circular polarization diversity with ACMSA and the geometry of the ACMSA are described.