In this paper the Full-Wave design method of the non-resonant waveguide multislots antenna is presented. The internal mutual couplings between adjacent radiating slots are considered in the described method. The problem of the physical nonrealizability of some equivalent currents amplitude distributions feeding slots, caused by the internal mutual couplings between slots is also presented. Some corrective solutions which allow solving mentioned problem are proposed. In order to confirm the usefulness of the presented solutions the obtained results are compared to their equivalents reached in computer simulations with the use of CST Microwave Studio.