This work describes the design and simulation of a GTEM - Gigahertz Transverse Electromagnetic chamber. The GTEM is intended to be used for EMC-EMI/EMS pre-compliance tests on automotive electronic boards and integrated circuits. The physical conception chamber is shown for a range from 500 MHz - 18 GHz. As a crucial step in the design, the APEX (match between RF excitation and the body of the chamber) is minutely shown. The structure designed has significant advantages over the conventional available, mainly in economic terms and on the operational frequency range.