On the role of essential higher order modes in a GTEM cell

The GTEM cell essentially combines the elements of a transmission line and anechoic chamber. Power absorption is therefore a mutual phenomenon between the lumped element resistors and the high frequency absorbers. The different locations of the two absorbers require change in the energy flow. Investigation of this energy flow shows that essential higher order modes play a significant role in the transition between the two regime. In fact, once above the cutoff, higher order TM modes generate eddy regions within the cell. These eddies act as a barrier in the regions where they are located. As a consequence, most of the high frequency energy is linked to the lumped elements which can only absorbs low frequency energy. This results in a poor performance of the hybrid termination of the cell.