Model for the patch radiator with a perturbation to achieve circular polarization

Some models have been proposed for the equivalent circuit of the patch antenna with a perturbation (central slots, gaps at the edges etc. ) in order to get circular polarization. These models make, in some cases, a qualitative description of the behaviour of the patch but without foreseeing its behaviour concerning AR (axial ratio) and reflection coefficient, versus frequency, or in other cases their results are not accurate, in the authors´ knowledge, in all the parameters mentioned. They propose a simple model allowing, starting from measurements of the patch alone or from its design parameters, them to foresee the optimum frequency at which circular polarization will be achieved by means of a perturbation (central slot or other), the AR versus frequency (and so the bandwidth in circular polarization) and even the reflection coefficient versus frequency (matching bandwidth). The model has been applied to several circular patches (at different frequencies, and with different thickness of substrates) showing a very good agreement with the experimental results