This work focused on HF RFID systems, where it was a goal to increase the reliability of the system. Especially in environments with metallic parts many problems occur. It became clear that many problems took place at the loop antenna of the RFID system. Therefore, we focussed on the design of loop antennas in order to increase the reliability of HF RFID systems. Although HF RFID systems are widely adopted by the industry, it was shown that the implementation of an RFID system for a specific environment involves a lot of design choices. Considering the loop antenna, several important design parameters have to be taken into account if we are aiming for a proper functioning HF RFID system. Metal objects in the vicinity of the loop antenna can have a high impact on the functionality of the system. In some cases a redesign of the loop antenna is needed. A redefinition of several design parameters and a solution, in terms of a new antenna concept, was proposed to take care of metal objects in the vicinity of the antenna. It has been made clear that an environment with metal objects has to be handled with care. If we only consider simple environments with one metal plate or object, we can design the loop antenna analytically. But when the environment becomes more complex, one needs a strong tool to create a reliable loop antenna for these environments. The main result of this thesis is the creation of an automated antenna design tool (AADT) which takes care of metals in the vicinity and creates an optimized loop antenna. The optimized loop antennas are based on parametric shapes and self-defined RFID goal functions. Two practical and challenging test cases served as an evaluation of the AADT in which an optimized loop antenna was implemented. In both cases, we created a reliable HF RFID system, which always met the specified requirements. At all time, measurements confirmed the simulation results.