The mutual coupling between antennas is an important parameter in multi-antenna systems that needs to be controlled in order to ensure the performance of all involved components. While full-wave simulations are accurate in estimating the mutual coupling, they remain computationally expensive for large structures and are sometimes even impossible due to the lack of definition in early design stages of a system. This work summarizes the different coupling mechanisms between patch antennas and proposes a modified two-ray model technique in order to quickly estimate the mutual coupling. The proposed method is shown to agree well with full-wave simulations in the given scenarios and has the advantage of giving physical insight into the coupling mechanism especially with respect to polarization that then can be further utilized in developing methods to mitigate the mutual coupling.