Analysis of large E field generators in semi-anechoic chambers used for full vehicle immunity testing: Numerical and measured results

There are several standards that recommend the use of transmission line systems (TLS) as the field generation equipment for immunity testing. In general the assumption is that these systems provide a uniform field that will illuminate the whole vehicle under test. Additionally, It is commonly assumed that these systems do not radiate and that the shielded semi-anechoic chamber has no effect on their performance. In this paper the reader will be educated on two facts. First, that the TEM field supported by these structures is not perfectly uniform over the volume occupied by the vehicle at all frequencies. Second, that the structure will radiate and that it will couple to the chamber enclosure. The coupling will produce potential resonances at certain frequencies depending on the size of the chamber.