Stacked microstrip antennas for broadband circular polarization

Several microstrip antenna (MSA) configurations are available to generate the circular polarization (CP), which can be obtained by either single feed or dual feed. Square or circular MSA fed at two orthogonal points with equal amplitude and 90/spl deg/ phase difference yields wider axial ratio bandwidth than the single feed MSA, but the VSWR bandwidth is small. In this paper, several stacked MSA configurations using either square or circular patches have been proposed to increase both the axial ratio and VSWR bandwidths with higher directivity. Only one patch at the bottom layer is fed at two orthogonal points with equal amplitude and 90/spl deg/ phase difference, and the other parasitic square or circular patches are stacked to yield broadband CP. These antennas have been analyzed using the IE3D software based on the method of moments.