Characterization of large TEM cells and their interaction with large DUT for vehicle immunity testing and antenna factor determination

Transverse electromagnetic mode (TEM) cell testing of vehicles using a practical sized cell necessitates accommodation of a test object, the vehicle under test (DUT), higher than one third of the floor to septum height. Testing may be for immunity or for the determination of the vehicle´s antenna factor in the 150 kHz to 6 MHz frequency range. For this frequency range the environmental E-field is vertically polarized as is the TEM cell field, therefore the TEM cell should be useful for vehicle antenna factor measurements. A method is presented for overcoming the one third height `rule-of-thumb´ for TEM cells which allows useful antenna factor measurements and an estimation of the field the vehicle is subjected to in immunity tests. The DUT causes an impedance discontinuity and the estimation of the corrected field strength, based on the decrease of the `free space´ between the septum and the enclosure, is evaluated