This article presents a compact dielectric-loaded antenna (DLA) module with three coplanar polarizations for the first time. It has three monopole radiators spaced by with high isolations of around 20 dB for multi-input-multi-output (MIMO) applications. The three radiators are surrounded by a cylindrical dielectric block with a diameter of only. The loaded dielectric block helps to reduce the mutual coupling by providing dielectric-air boundaries. In addition, it modifies the -field distribution to generate three coplanar polarizations. As can be shown by the envelope correlation coefficients (ECCs) based on radiation patterns, the proposed module can provide three independent channels for MIMO applications. Compared with an ideal single-input-single-output (SISO) system, our module can reach an ergodic channel capacity of around 282%. Based on the DLA module, a compact high-gain hexagonal antenna array (HAA) with coplanar tripolarization is proposed for long-distance MIMO applications. Dielectric-filled bow-tie-shaped slots are employed between DLA modules to reduce the intermodule mutual coupling. Moreover, a hexagonal artificial magnetic conductor (AMC) structure is arranged on the backside to reduce the backside lobes. As a result, a measured realized gain of more than 12 dBi is obtained for each polarization. According to the measured ECC levels, a MIMO system with our HAA can provide an ergodic channel capacity of around 244% of an ideal SISO system.