In this letter, a novel method of two-dimensional (2-D) self-decoupling at both E- and H-planes is proposed on the basis of the field-redistributed TM₁₂-mode circular patch antenna. At first, it is demonstrated the marginal field of patch is the main cause of coupling, and E-plane-coupled (H-plane-coupled) array suffers from electric (magnetic) coupling. Then, it is discovered for the first time that the TM₁₂-mode circular patch antenna is immune to the H-plane coupling, because its fields are null at two marginal regions along H-plane. After that, the slot loading for sidelobe reduction is further developed for field reshaping, and two cascaded slots help to generate two new marginal weak-field regions along the E-plane. The initial strong electric coupling in the E-plane is thus eliminated. In particular, the proposed self-decoupling method is applicable for larger-scale 2-D arrays with arbitrary element number, and it is demonstrated by 1×4 E-/H-plane-coupled arrays and the 2×2 arrays. At last, a prototype of 2×2 high-isolation MIMO array with 0.2-mm patch-to-patch separation is fabricated and measured. The array can achieve intrinsic high isolation of more than 20 dB, element gain of 10.7 dBi, and cross-polarization level below -20 dBi, without using any extra decoupling network.