In this paper, we propose a method to calculate the magnetic field in Flux Concentration Superconducting Magnetic Coupling (FCSMC) with rectangular permanent magnets (PMs). The inner rotor is composed of rectangular PMs and the external one is made of High Temperature Superconducting (HTS) coils supplied by DC current. Firstly, an exact 2-dimensional analytical computation is developed in polar coordinates for calculating the magnetic field distribution in FCSMC with sector PMs having the same volume as the rectangular ones. The model is validated by finite element computations. The analytical model is then used to predict the performances of FCSMC. The electric loadability of the FCSMC is determined by considering the dependence of the critical current vs. the flux density distribution. A parametric study showed that the analytical model can predict the torque with a reasonable precision. Therefore, this model can usefully be used for optimization purposes where reductions in computation time are needed.