This study describes a structure design of the Gigaherz Transverse Electromagnetic (GTEM) cell for electromagnetic tests in biological systems. Using electromagnetic simulation software we show that the optimization of final structure assures the criteria imposed on a low level of reflection towards the radio frequency generator, and a fairly uniform field in the test zone. A sensitivity study was also conducted when the cell was loaded with a few samples under test. We report that the level of reflection remains adequate as long as the test volume remains limited in relation to the size of the cell. The first estimation results on the SAR values are consistent with the distribution of the fields in the cell. A cell was fabricated with the design data, and tested for the reflection level. The measurements confirm the results of simulations.