The effect of a low dielectric block placed at the tip of a GTEM cell on the electric field was numerically and experimentally investigated from 1-16GHz. The block increased the electric field strength when placed at the GTEM cell tip. Comparison of the simulation and measurement results revealed good agreement between them. However, we also confirmed that when the low dielectric block was installed in a location far from the GTEM cell tip, it had little influence on the electric field, regardless of its size. It is concluded that a low dielectric material increases the electric field strength when it is placed at the tip of a GTEM cell.