In this paper, a four port disk shaped compact multiple input multiple output (MIMO) patch antenna for vehicular application is proposed and fabricated. The structure is composed of a circle patch with cross slot combined to an annular ring patch. The structure is analyzed by using Theory of Characteristic Modes (TCM). The inner and outer part of the antenna operated at its TM11 and TM21 modes respectively. As a result, four different radiation patterns are achieved. The antenna exhibits a mutual coupling between the four input ports less than −16dB in simulation and −18dB in measurement in the frequency band. Both simulated and experimental results have been presented and discussed.