Gain improvement of an array of sequentially rotated circularly polarized microstrip antennas using stacked parasitic patches

Sequentially rotated microstrip array antennas have been extensively used for circularly polarized radiation due to their wide VSWR bandwidth and polarization purity; however, in many cases, these arrays do not meet gain requirements. Stacked parasitic patches have been used to improve the gain of an array of sequentially rotated circularly polarized microstrip antennas. The gain can be improved within 2.5-3.2 dB by adding one parasitic patch to each array element, or 3-4 dB by adding two parasitic patches per element, with minor side effects on axial ratio. The dependence of the gain improvement on the height and size of the parasitic patches has been studied and verified by simulations. It is found that there are multiple local maxima in the curve of the gain versus the height of the parasitic patch. The maxima occur at heights near to multiples of a half of the wavelength in the spacer medium. Since the parasitic patches are fabricated on low dielectric constant substrates and are separated from the exciting patch by spacer or foam, this method of gain improvement is very simple and at the same time cost-effective.